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Turf and Bees: What's the buzz on pesticides in lawns?

By Ian Lane, Graduate Research Assistant

If you have been paying attention to the news lately, you know that bees have been making headlines. News outlets have done an amazing job of helping scientists sound the alarm on unsettling declines in bee pollinators. While we have good evidence for declines in honey bees and some of their cousins, the bumble bees, the cause of this decline is hard to pinpoint. Current thinking in the scientific community puts the decline down to a number of interacting factors, including reduction in stable food sources, introduction of bee diseases, and the irresponsible use of insecticides. While it's difficult to tease apart how these factors interact, we do have some good knowledge about how lawns fit into this theoretical framework.

Sam Bauer

Photo 1: White clover and dandelion can provide great early season forage for pollinators in lawns


Lawns are home to a number of weeds that are the bane of homeowners. While our gut reaction may be to reach for a herbicide, it's worth noting that many weeds actually can provide high quality forage for bees. Two of the most important lawn forage plants are the common dandelion (Taraxacum officinale) and Dutch white clover (Trifolium repens). Dandelions are one of the earliest, and often only, blooming flowers of spring. This early source of pollen and nectar is essential to overwintering honey bee colonies as they begin the process of raising new workers. White clover is another spring bloomer (though not as early) that provides highly nutritious pollen throughout the year. While the exact nature of bee's relationship with these flowers isn't widely studied, recent research at the University of Kentucky sought to characterize the types of bees visiting dandelions and clover. They found surprising diversity on white clover, including a number of at risk bumble bees (Larson et al. 2014). Similar preliminary research here at the University of Minnesota confirms many of their findings.

There may also be some solutions for homeowners looking to control weeds but leave clover in their lawn. One common herbicide known as 2,4-D is effective on many broadleaf weeds, but generally ineffective on clover. Small demonstration trials at the University of Minnesota confirm that 2,4-D has relatively low action on clover but is relatively effective against other weeds.


The another type of pesticide that can make a big impact on bees are insecticides . Much of the recent attention on pollinators has focused on a class of insecticides known as the neonicitinoids. Neonicitinoids are used in turf to help control a number of insect pests, most importantly grubs. They work by "dissolving" into the irrigation water or rain, which is then taken up by the plant and becomes part of the leaf and root tissue. This ensures that any insect munching on the tissues of your grass gets a lethal dose, and your lawn stays green. While bees would never have a reason to take a bite of your grass, your helpful lawn weeds are a different story. It turns out that not only do these insecticides move into plant leaves and roots, but the nectar and pollen of the flowering weeds as well.

Many studies have looked to see if neonicitinoids applied to lawns full of clover have negative effects on bumblebee colonies. The researchers in Kentucky do this by getting a colony of the commercially available common eastern bumble bee (Bombus impatiens), placing it on a patch of flowering clover that is treated with a neonicitinoid, then caging them so they are forced to forage on the treated clover. These experiments are always accompanied with a similar set-up but on a non-treated patch as a point of comparison. Here again the University of Kentucky has been leading the way with a study published in 2002 (Gels et al. 2002) that found if imidacloprid (a type of neonicitinoid) was applied to flowering turf without any post application irrigation that bumble bee colonies suffered worker weight loss, increased worker death, and sluggish behavior. However, if irrigation was applied directly following these imidacloprid applications, no negative responses were seen.

Similar responses were seen in a study investigating clothianidin, another type of neonicitinoid (Larson et al. 2013). Bumble bee colonies that were confined over patches of flowering clover, and that had the high label rates of clothianidin applied to the turf, saw dramatic effects on the number of workers, new queens, as well as total colony weight when compared to control colonies. The effects of irrigation were not part of this study, but when clover nectar from nearby sights that had been applied with clothianidin were sampled, they found high amounts of the neonicitinoid. This study's main aim was to compare clothianidin to a new chemistry of insecticides called anthranilic diamide (specifically chlorantraniliprole). This new class of chemical had seemingly no adverse effects on bumble bee colonies when compared to the controls. While there is more research to be done, this is a promising alternative to neonicitinoids for insect control in turf. You can currently purchase chlorantraniliprole for use on residential and commercial turf, and trade names include "Scott's Grubex" or Syngenta's "Acelepryn".

While urban landscapes and lawns are only one part of a very large system, they are nevertheless an important part of a vast majority of people's lives. Promoting animal diversity in urban landscapes, be it pollinator or other, helps improve important issues related to stormwater runoff (rain gardens and buffer strips) and urban agriculture (pollination and biocontrol services) and also enriches everyday life through learning opportunities and aesthetic value. Even the smallest effort, such as leaving some weedy flowers or choosing a safer insecticide, may make a difference.

Stay Informed

A new series on pollinators is being offered by the University of Minnesota Landscape Arboretum. "Pollinators: What you need to know and how to make a difference" is a 3-part series focusing on: 1) Plants and People, 2) Pesticides and Other Problems, and 3) Policies and Politics.

The Minnesota Turf and Grounds Foundation will be offering a 1-day session on Super Tuesday of the Northern Green Expo, January 13th, 2015. "Bee Aware: The importance of pollinators in the landscape" will feature expert presenters discussing real world issues surrounding pollinators, as well as practical strategies to promote them in the landscape. Stay tuned to as this program develops.

Works Referenced

Gels, J. A., D. W. Held, and D. A. Potter. 2002. Hazards of Insecticides to the Bumble Bees Bombus impatiens (Hymenoptera : Apidae ) Foraging on Flowering White Clover in Turf. J. Econ. Entomol. 95: 722-728.

Larson, J. L., A. J. Kesheimer, and D. A. Potter. 2014. Pollinator assemblages on dandelions and white clover in urban and suburban lawns. J. Insect Conserv. 18: 863-873

Larson, J. L., C. T. Redmond, and D. A. Potter. 2013. Assessing insecticide hazard to bumble bees foraging on flowering weeds in treated lawns. PLoS One. 8: e66375.

Repairing Lawns Following Flooding

The month of June was a wet one. Many homeowners, grounds managers, and golf course superintendents are finally starting to see some of the flood waters recede, although standing water is still covering many of our landscapes. The University of Minnesota's Climatology Working Group is calling June of 2014 the wettest month on record. In the Twin Cities we saw 11.36 inches of rain for the month, almost 7 inches above average and falling just short of the 11.67 inch record set in 1874.

We are starting to see a wide range of damage to lawns and turfgrass throughout the state. In situations where standing water was present for greater than 7-10 days, the turf is almost certainly dead and will need to be repaired. Turfgrass covered for less time has a greater chance of recovery, but every situation is different. Unfortunately, there is not good information regarding how long turfgrass can survive under standing water because there are so many potential mechanisms of damage. These mechanisms can be separated into 2 groups: primary damage from waterlogging and secondary damage after the water has gone.

Primary damage includes such factors as water temperature and water depth. Water temperature will probably be the most important factor determining survival, with turfgrass death occurring in only a few days when water temperatures are 80 degrees F and higher (note: we did not see water temperatures this high during recent floods, unless it was very shallow and stagnant). When water temperatures are lower the turf can still die, with lack of oxygen being the primary culprit. If the turf is completely submerged, this will be a worse case than if some of the leaves and crowns are exposed.

Secondary damage might be associated with sediment buildup, fungal diseases, moss and algae, and weed infestation. While we have very little control over the primary mechanisms causing damage, now is the time to start thinking about how to reduce damage that could be caused by the secondary mechanisms. The primary disease you could expect to occur after flooding is pythium blight. Look for circular or irregular patterns of dead turf inside of healthy turf areas. For more information on pythium blight, follow this link to a fact sheet from Purdue University Extension: Pythium Blight. Remember that plant disease samples can be submitted to the University of Minnesota Plant Disease Clinic for correct identification and control recommendations. If you have confirmed that you lawn is infected with pythium or other diseases, I recommend contacting a lawn care contractor to carry out the control measures.

To this point I've been recommending that homeowners be patient and assess the damage as it presents itself. Turf that appears to be dead following the receding of flood waters should be monitored for several days; if no green tissue appears within 7-10 days, you can assume it is dead and should start forming a renovation plan. In many cases, you might be surprised with the amount of turf that recovers when the conditions are right. In situations where sediment or debris buildup has occurred, you will want to act fast to remove it. The previous Turfgrass Extension Educator, Bob Mugaas, wrote a great article addressing repair of areas where sediment has built up in the 2010 edition of the Yard and Garden News. That article can be found here: Repairing Flooded Lawns

Timing of repair can be difficult. The cool-season grasses that we grow in Minnesota do not establish well in the middle of the summer due to the high heat and diseases that may occur. If at all possible, I recommend waiting to seed until temperatures cool in the early fall around mid- to late-August. Fall seeded lawns will have a much better chance of a successful establishment. With that being said, recovery in the short term could be promoted by aerating your soil once it is dry and/or applying light rates of nitrogen based fertilizer.

Choice of turfgrass seed can be very important. If flooding is a common occurrence on your lawn, I would recommend Kentucky bluegrass over perennial ryegrass or fine fescues. The University of Minnesota Extension has numerous resources to help you in repair process. Please follow these links for more information:

Purchasing Turfgrass Seed

Finding the Right Grass Seed

Renovating an Existing Lawn

Lawn Diseases

Weed Control

Finally, feel free to reach out if we can be of help. You can contact me directly at: or 763-767-3518

Damaged Lawns: Steps to Bringing Some Life Back

Sam Bauer, UMN Extension- Turfgrass Science
Spring Damage
The grass-growing season is in full swing, and for some of you this means repairing turfgrass areas that were impacted by winter injury. By now, it should be apparent which areas of your lawn were damaged (but not killed) from winter stresses and which areas will not recover from winter injury. Plants that are slowly recovering, suffered damage only to the leaves and are able to produce new leaves during the spring. Practices such as removing dead leaf tissue and fertilizing will help expedite the recovery of these areas. In contrast, plants that are dead suffered damage to the crown tissue (survival organ of turfgrasses) and will need to be renovated and repaired. The goal of this post is to provide you with information on the different types of winter stresses that effect turfgrass plants and the cultural practices that can be used to minimize winter injury. In addition, a step-by-step outline of the recovery/renovation process is provided.

Repairing dead turfgrass on a yearly basis can be both time and labor intensive and is an unnecessary added expense. Therefore, one of the first steps to minimizing winter injury is to identify the primary cause of damage. In Minnesota, damage detected in the spring may be attributed to several different stresses that the turfgrass is exposed to during winter months. Specifically, there are five main stresses associated with low temperatures and each has the potential to cause damage and/or death of your lawn. Crown hydration is associated with elevated temperatures (above freezing) and results in an increase in water content of the turfgrass plant. This can be lethal if hydrated tissues are then re-exposed to freezing temperatures causing ice crystals to rupture cells in the leaves and crown. Desiccation causes severe dehydration of plant tissues due to lack of snow cover or inadequate moisture and is generally a problem on elevated areas exposed to wind. Prolonged ice cover can also be damaging to lawns by creating an impermeable layer above the turf resulting in a depletion of oxygen and a build up of gasses that are toxic to lawn grasses. Additionally, grasses can die simply from exposure to low temperatures; however, damage associated with temperatures at or below freezing is minor during winters with adequate snow cover. Finally, snow molds are a common occurrence in Minnesota and winter damage associated with these diseases occur every year. For more information on snow molds, visit this article by Michelle Grabowski: Altogether, these stresses can occur individually or as a complex to cause damage that potentially could be lethal to the turfgrass in your lawn.

Along with the five mechanisms causing winter injury to lawns, there are also many other abiotic stresses that occur throughout the spring period. Salt loading from the use of de-icing salts commonly causes damage to turf along roadsides, sidewalks, and driveways. Primarily, these salts cause severe desiccation of leaf and crown tissue and ultimately result in death of the turfgrass plant. By the time the salts are leached through the soil profile with spring rains, most of the damage has been done. In addition to deicing salts, dog urine spots can kill grass from the high salt content and can cause excessive growth due to nitrogen in the urine. Mechanical damage caused by snowplows, mowing too early, and power raking early in the season can also result in areas of turfgrass that need to be repaired in the spring.

Preventing/minimizing winter injury is a yearlong process and involves knowing your lawn and carefully considering the maintenance practices utilized to maintain the turfgrass. For example, in areas that frequently accumulate standing water, core aeration will help with water infiltration as snow melts in response to warming temperatures. Overall, this will reduce the potential for crown hydration and ice crystal formation along with helping to prevent the establishment of an impermeable ice layer. An additional consideration is fertility, specifically associated with the application of nitrogen. Snow molds are more common on lush, succulent turf, and a heavy application of nitrogen in the fall could promote damage caused by snow molds. In addition, succulent turf is more prone to injury attributed to exposure to temperatures at or below freezing. Keep in mind that as summer transitions into fall keep the cultural practices implemented have a direct impact on the survival of turfgrass plants throughout the winter and into spring.

Steps for Recovery
Providing the right conditions for your lawn to thrive is the most important component of a good recovery program. While it's up to Mother Nature to supply the main ingredients, maintenance practices should focus on creating the optimum growing environment for the turfgrass species in your lawn. The following steps outline the processes required for repairing damaged/dead areas of your lawn and also cover factors to consider for managing the overall health of turfgrasses.

1. Choose a mixture of grass to be planted. This is also where the choice of seeding or sodding comes into play. Sod is good for situations where you desire instant turf cover and quick stabilization. With sod, your species and variety options will be limited because not all grasses form an acceptable sod. Kentucky bluegrass is the standard for sod in Minnesota due to its high aesthetic quality and extensive rhizomes that aid in holding the sod together. Recently, fine fescues have been included in specific sod mixtures for the use on roadsides because of their good performance in high salt environments. This sod also makes a great low maintenance option for home lawns. A list of suppliers of this sod can be found here:
Sod must be watered daily (more frequently in heat and drought) for the initial week, in the absence of rain. Watering should be focused on wetting the sod and the underlying soil; however, after roots emerge from the sod, irrigation should be less frequent in order to encourage further root growth. Seed should generally be watered multiple times a day lightly. The trick here is to keep the surface moist during the germination period. Excessively wet conditions will cause deterioration of seed and seedlings, and encourage turf diseases and weeds. Remember to avoid watering when precipitation is sufficient.
For help finding the right grass species and seed, visit these resources:

Turfgrasses for Minnesota lawns

Finding the right grass seed

Purchasing turfgrass seed

2. Prepare the area for seeding or sodding. No matter which method of establishment you've chosen, preparation of the surface will generally be the same. The surface should be smooth, weed-free, and not compacted. If seeding into existing grasses, a slit-seeder or vertical mower can be beneficial to ensure good seed to soil contact, but be sure not to plant the seeds too deep (1/4" would be the maximum depth to plant seed). In addition, aeration followed by seeding can also be very successful. For sod, removing existing vegetation and smoothing the surface should prepare areas. The thickness of sod is generally around 1.5 to 2" and this should be accounted for when preparing an area to be sodded. In addition, soil tests can be conducted at this time to determine nutrient status and unfavorable conditions in your soil. Soil samples can be submitted to the U of M Soil Testing Laboratory

3. Apply fertilizer and/or soil amendments as determined by your soil test. If you don't have a soil test, a general recommendation for establishment of seed or sod is to apply a starter fertilizer (high phosphorus, ex. 10-20-10) at a rate of 1lb phosphorus per 1000ft.sq. If the fertilizer in the example is chosen, this would also supply 0.5lb of both nitrogen and potassium. If applying fertilizer only, you have the option to put it down before or after seeding, or above or below sod.

4. Plant seeding or install sod. For seed, be sure to check the seed label for the proper rate. Kentucky bluegrass should be seeded at 1.5 to 2lb per 1000ft.sq, whereas fine fescues should be seeded at 4 to 5lb. Seed can be applied by hand, or preferably with a drop-type spreader. Rake the seed lightly into the soil surface. If sodding, take care to tightly pull the sod seams together. The seams of sod rolls should be staggered in a brick like pattern to avoid channels for water movement. And sod should be installed perpendicular to slopes.

5. TLC. This last step is one of the most important for successful establishment of your new grass. Particularly, moisture content of the surface and soil will be a major determining factor on the recovery rate of those damaged or dead areas. The amount of water necessary for turfgrass establishment varies greatly and depends on factors such as soil type, air temperature, and whether the area has been seeded or sodded. Consequently, monitoring the newly renovated area(s) is key to ensuring that irrigation isn't being over or under applied.

We see sod die and seedlings lost from both over- and under-watering. Unfortunately, there's no general formula for success from a watering standpoint. For seed, the surface should be maintained moist like a sponge. During hot and dry periods this might mean watering 3-4 times per day with 0.05 to 0.10" each time. As seedlings emerge, the amount and frequency of watering can be reduced and this typically occurs approximately 1 to 2 weeks after seeding. For sod, irrigation should be frequent during the first couple of days; however, this should be reduced in order to encourage rooting into the underlying soil. Sodded lawns will benefit greatly from several core aerations in the initial years.

A follow-up fertilizer application can be applied around 2 weeks after seeding to encourage establishment and density. Sod can be mown rather quickly, possibly even a week after being installed if using a hand-operated mower. Larger mowers can damage sod if they are used too soon; before operating large equipment on sod, check to be sure the sod is rooted into the soil. Seeded areas can be cut just as the grass starts to grow beyond the desired height of cut, generally 2.5 to 3" for lawns. Getting seeded areas mown soon will help to reduce weeds and encourage density in the turf, be sure to use lightweight equipment.

By using these five steps you should be able to recover even some of the worst lawn situations. Remember, choose the right plant for the right place and maintain balanced moisture. These are the most important factors throughout the recovery process.

Karl Foord, Extension Educator - Horticulture

Karl Foord

Photo 1: Honey bee on dandelion

Karl Foord

Photo 2: Honey bee on Dandelion

Karl Foord

Photo 3: Split and curled stigmas of dandelion

Karl Foord

Photo 4: Dandelion stigmas & honey bee corbicula

Karl Foord

Photo 5: Native Mining bee (Andrena spp.)

Karl Foord

Photo 6: putative - Plasterer Bee (Colletes spp.)

Karl Foord

Photo 7: Native Small Carpenter Bee (Male) (Ceratina spp.)

For years I used to fight the dandelions in my lawn. I used herbicides and a small trowel. It was a bit of a losing battle as there is a third of an acre of school property adjacent to mine where dandelions are not controlled. This being separate from the nearby sports fields where the weeds are controlled. Imagine the number of dandelion seeds that blew into my yard each year.

As I have become more aware of pollinators, I have come to accept and perhaps even embrace the "noble" dandelion. Dandelions are an important source of pollen and nectar for bees early in the season when little else is flowering.

Given the problems facing our honey bees and native bees, it might be worth reconsidering dandelions and what they contribute to pollinator health. So with my new attitude I took camera in hand and ventured into the dandelion patch (Photo 1).

Consider how artistic is the dandelion flower when viewed close-up (Photo 2). The flowers each have split lobed stigmas that curl back and sometimes twist into shapes similar to the letter F shape holes cut into violins (Photo 3). Consider also the beautiful orange color of the dandelion pollen as attached to the corbicula or pollen basket of the honey bees (Photo 4).

The dandelion also provides nectar and pollen for our native bees: Mining Bees (Andrena spp.) (Photo 5), Plasterer Bees (Colletes spp.) (Photo 6), and Small Carpenter Bees (Ceratina spp.) (Photo 7). If you use your lawn for recreation and need a dense turf as a playing surface, you may want to control dandelions. However if this is not the way you use your turf, please consider letting some of the dandelions provide forage for our pollinators. In this way you can be a part of the solution to the ills facing our pollinators.

Dear Yard and Garden News Readers,

For those of you that are interested in learning more about lawn care and turfgrass science but have been unable to attend the School of Turfgrass Management in the past, we've developed a new offering for you, The 2014 Great Lakes School of Turfgrass Science. Much like the traditional turf school, this class was designed as a basic foundation of turfgrass science education for those that don't have a formal degree in turfgrass science or those looking for a refresher. Along with the traditional instructors from the University of Minnesota (Sam Bauer and Dr. Brian Horgan) and the University of Wisconsin-Madison (Dr. Doug Soldat, Dr. Paul Koch, and Dr. Chris Williamson), we've also added instructors from five other universities:

Dr. Dave Chalmers- South Dakota State
Dr. Kevin Frank- Michigan State
Dr. Dave Gardner- Ohio State
Dr. Aaron Patton- Purdue
Dr. Frank Rossi- Cornell University

This ten person team of instructors brings a whole new level of turfgrass science knowledge to this short course. Other features of the new format include:

- Fully online course; view session live on Wednesday nights from 6-8pm or watch the recordings

- Half the cost of the traditional School of Turfgrass Management

- Topics relevant to 21st Century Turfgrass Management

- The opportunity to take part from the comfort of your home or workplace

If you have any questions regarding this new school, please contact me at:

Sam Bauer

Good Question: Do you really need to rake all those leaves?

Good question.png

View Video On WCCO

Here is some really good information for all of you homeowners looking to avoid the leaf raking process this weekend. The real answer to this question is NO, but it comes with one catch......he most important point with fall cleanup is that the tree leaves are not covering a significant portion of the turfgrass canopy. 10-20% coverage of your lawn might be okay, but I certainly would make sure the leaves aren't covering any more than that. Excessive leaf matter on your lawn going into winter is bad for several reasons. First, it will smother the grass and if not removed very soon in the spring it will inhibit growth. Second, it can promote the snow mold diseases. And finally, turf damage from critters (voles, mice) can be more extensive in the spring.

The homeowner basically has three options to make sure that leaves are not covering a significant portion of their lawn:

1) Rake them up or use a blower- compost the leaves or dispose of them

2) Use the bagging attachment for your mower: compost the leaf/grass mix or dispose of

3) Mulch the leaves with a mower (i.e. chop them into small pieces so they will fall into the canopy). This is my preferred option because the nutrients and organic matter will benefit the lawn and soil. Some leaf types have been shown to reduce weed seed germination when mulched into a lawn canopy (maples, others). The leaves of some particular tree species (legumes like honey locust, others) might actually add a significant amount of nitrogen to lawns because these species fix nitrogen from the atmosphere just like soybeans, so higher leaf nitrogen contents in these leaves is possible. Additional resources for these two concepts are here:

tree leaves and weeds.pdf

N content tree leaves.pdf

There's Still Time to Dormant Seed Your Lawn

For over a month now I've been receiving questions that go something like this, "I know I missed the best time for seeding my lawn which is mid-August to mid-September. Can I still seed even though it's October and temperatures have been mild?" My response is always the same, "Just wait, dormant seeding in November will be your best option." It is very true that if temperatures are warm during the month of October, you could get some seed to establish prior to winter, but temperatures are unpredictable and could change drastically within a day.


Photo 1: Tired of your lawn looking like this every spring. Consider dormant seeding this fall to improve your spring lawn quality.Sam Bauer.

So, what do/did you risk by seeding in October? Well nothing really, except the cost of seed. Chances are that a good majority of this seed will germinate prior to winter, and complete loss of seedlings is possible over the cold winter months. Because of this, your time and money are better spent waiting for the appropriate dormant seeding time which is generally mid- to end-November.

Dormant seeding can be conducted with any turfgrass species. This practice involves seeding when temperatures are too low for the seed to germinate prior to winter. Germination prior to winter is bad and seedlings will generally die if they haven't matured. Sometimes it is a bit of a waiting game at this time of year. The trick is to find the time when soils are unfrozen so that seed can be worked in slightly, yet air temperatures must be cold enough so the seed won't germinate. Wait for high daytime temperatures of 35-40 degrees before seeding. You still should be waiting at least two weeks to seed based on the long range forecast for the Twin Cities. Regions of northern Minnesota will be able to seed much sooner, possibly even next week.

Is there an advantage to dormant seeding versus spring seeding? Yes and no. A dormant seeded lawn could mature as much as one month faster in the spring than a spring seeded lawn. This is because some of the germination process actually starts prior to winter in a dormant seed situation, although the shoots still haven't emerged from the seed. When temperatures are adequate in the spring, complete germination occurs. In this case the seed actually dictates when temperatures are warm enough to grow. Just like late-fall, temperatures and weather patterns can be unpredictable in the spring. For this reason, the best timing for spring seeding is difficult to predict, which can delay the timing to actually sow seed. Still, there some negative aspects of dormant seeding to consider. First, because of the spring temperature fluctuations, it is possible to have good seedling establishment initially, but a cold spell during this time will injure these seedlings. Also, there is a greater potential for seed loss over the winter due to erosion and water movement, predation, and decay. These positive and negative aspects should always be considered during this process.

Bob Mugaas wrote a fantastic article in the November 2009 issue of Yard and Garden News. Please visit this article by clicking the link for more detail on the dormant seeding process: Dormant Seeding Lawns

For turfgrass seeding options, have a look at the University of Minnesota Turfgrass Science Page

Snow Molds Blight Minnesota Lawns - For Now

M. Grabowski, UMN Extension

Photo 1: Pink and gray snow mold on a Minnesota lawn

Michelle Grabowski, UMN Extension Educator

Persistent cold weather and late snow fall mixed with freezing rain have created ideal conditions for the growth of snow molds this year. Snow molds are caused by fungal pathogens that thrive in cold temperatures (just above freezing to about 60F) and high humidity.

M.Grabowski, UMN Extension

Photo 2: Small round patch of pink snow mold with a light center and dark border

Two types of snow mold are common in Minnesota. Pink snow mold, caused by the fungus Microdochium nivale, results in round dead patches in lawns that can be an inch or two across or as large as a dinner plate. These dead patches are often pale tan in color, matted down and may have a dark brown border. In sunlight pink snow mold patches turn pink to salmon colored as the fungus produces spores of these colors.

M.Grabowski, UMN Extension

Photo 3: Pink matted grass in a pink snow mold patch

Gray snow mold, caused by several species of Typhula, also cause pale gray to tan patches of matted down brittle grass that can spread up to 3 feet across. If the matted down grass of gray snow mold is examined closely, gardeners can see small black dots, about the size of a pen tip. These black dots are sclerotia, resting structures produced by the fungus that allow it to survive through harsh conditions. It is not uncommon to find both pink and gray snow mold in the same lawn.

M.Grabowski, UMN Extension

Photo 3: Large irregular matted patch of gray snow mold

M.Grabowski, UMN Extension

Photo 5: Small black sclerotia of gray snow mold

The good news is that although snow molds thrive in cold wet conditions, they go dormant as the weather becomes warm and dry. In many cases the snow mold fungi blight the grass leaves but do not kill the crown. In these situations, the grass will recover as the fungal pathogen goes dormant. In severe cases of snow mold, the grass plant may die and gardeners will need to reseed the infected area.

For now there are a few things that gardeners can do to speed the fungal pathogen into dormancy. Remove or spread out any remaining snow piles, so the snow melts quickly and the grass below is exposed to sun and air. Rake the lawn to remove any leaf debris and to fluff up matted down patches of turf. This will help improve air movement around the grass plants so leaves dry quickly after dew or rain. A light application of fertilizer in the infected patch can help grass recover. If no recovery is seen, reseed the area, taking care to rake away matted down grass so that seed has good contact with the soil below. Fungicides are not effective in controlling snow mold once the disease is established and should not be used at this time of year.

Sam Bauer, Extension Turfgrass Educator

Hooray! It's finally time to start thinking about home lawn care again.  Last fall we were stressing the importance of maintaining moisture levels in your lawn amidst one of the worst droughts in Minnesota's history.  In case you've forgotten, the months of August through November alone saw an eight inch precipitation deficit in the Twin Cities area.  This translates to approximately 70% below average precipitation for the fall period.  Many other areas of the state, mainly northwestern and southern Minnesota, were in a much worse situation. 

Minnesota Climatology Working Group

Photo 1: Winter precipitation

Currently, 67 percent of Minnesota is in Extreme Drought or Severe Drought according to the University of Minnesota Climatology Working Group (Spoden, 2013).  Fortunately, total precipitation for 2013 is so far above average.  The climatology map on the left shows precipitation departures from normal for the first of the year until now.  The northwest region of the state has received as much as 2.5 inches of precipitation above normal.  Question: will this help to replenish soil moisture levels?  The simple answer is, well, not exactly. 

Currently soils are frozen.  Soil frost depths generally range from 0 up to 60 inches in Minnesota soils, and this takes time to thaw out in the spring.  This generally means that precipitation falling right now (on mostly frozen soil) does not get absorbed into the soil, but rather promotes the flooding that we experience every spring.  Even during slow spring thaws, the surface moisture melt will precede the defrosting of our soils, in which case most of the surface moisture will run off.  This means there is potential for spring flooding AND continuation of drought conditions.  Depending on your location in the state, you may need to consider preparing for flood or drought, possibly both. 

Flooded Lawns

Last spring we saw flooded lawns in many areas of the state.  Additionally, the floods near Duluth in June left many homeowners with silt covered turfgrass in need of repair.  If your home is in close proximity to any body of water, especially some of our main rivers like the Mississippi or the Minnesota, this may be nothing new to you.  However, it's always good to be prepared for worst case scenario situations. 

Randy Nelson

Photo 2: A spring flooded lawn - remedies - remove silt & debris, aerate, interseed

Consider these tips to help reduce the damage and recover from flooding:

* Sandbag high risk turf areas to reduce the extent of flooding and buildup of silt
* Remove all debris and silt from smothered turf areas as soon as possible
* Smothered turf should be aerated to allow the exchange of oxygen and encourage new growth
* Avoid planting perennial ryegrass, as it is generally less tolerant of flooding than other turfgrass species. 
* Consider completely renovating lawns that are not easily repaired

For more information on repairing spring flooded lawns, please see this Yard and Garden News Update from retired Extension Turfgrass Educator Bob Mugaas:

 Drought Stressed Lawns

It seems odd to be discussing both flooded and drought stressed lawns in the same article, but really this is the situation that we are potentially facing this spring.  Those of you that maintained sufficient soil moisture levels through supplemental irrigation last fall will be in a much better situation than those that chose to not water.  In many cases, even the slightest effort to provide your turfgrass with some moisture would have paid big dividends.  We also discussed dormant seeding last fall, which can be great practice to improve the quality of your lawn the following spring.  If you failed to irrigate and/or dormant seed, unfortunately you might have a lot of work to do this spring. 

Sam Bauer

Photo 3: A lawn left to go dormant last fall

Proper irrigation practices will be critical to promote a healthy lawn this spring.  Consider these irrigation tips for drought stressed lawns:

* Irrigate during the early morning hours to reduce the leaf wetness period which is prolonged by night watering. Avoid daytime irrigation, which has the potential to evaporate quickly and be blown off target

* Water sufficiently to replenish soil moisture

* Monitor daily soil moisture loss through evapotranspiration and replace only what is lost.  Follow this link for evapotranspiration values in your location:

* Make seasonal adjustments to your irrigation system or watering schedule based on rainfall and temperature.  In general, spring and fall watering should be heavy and infrequent, and summer watering should be light and frequent

* Measure the depth of water put out by your irrigation system or sprinkler over a certain time period.  This will be important in determining how long to run your irrigation cycle

For more information on proper irrigation practices, please follow these links:

Home irrigation systems:

Lawn watering practices:

Watering lawns and turf:

As always, call or email with questions: or 763-767-3518

Spoden, Greg. 2013. Drought Conditions: Update March 7, 2013. Minnesota Climatology Working Group. Online resource:

Sam Bauer, Extension Turfgrass Educator

There's no question that the fall drought has taken a major toll on many of the turfed landscapes in Minnesota. If you failed to maintain turf health through supplemental watering from August to October, you most likely have yet to make a damage assessment of your lawn. During the summer months we talk a lot about letting our lawns go dormant during a drought and waiting for rain to replenish soil moisture. This is nothing new. However, the duration of the fall drought has pushed our lawns to the limit, probably passed the limit in many cases. There are two main concerns: 1) how long can turf stay alive in a dormant state?, 2) will drought stressed turf properly harden off and survive the winter?

Sam Bauer

Photo 1: Drought stressed/dormant lawn

How long can turf stay alive in a dormant state?

There are no clear answers to this question and it really depends on many factors, including: turf species, traffic, management practices, and site conditions. We commonly hear that Kentucky bluegrass can survive for up to 2 months under drought dormancy, but there is no definite time frame due to all of the variables. From my experience, as long as the crown of the turf did not completely dry out, it should still be alive. I've been encouraging home owners to utilize the last part of the growing season (October) by watering to bring the lawn out of drought dormancy before winter. If you've done this, you should have a good idea just how bad the damage is.

Will a drought stressed lawn survive the winter?

Probably not, and chances are that it may be dead already if you didn't provide at least some supplemental watering to keep the crown from drying out. Turf species will play a very important role here. Perennial ryegrass will be the least tolerant of drought conditions and cold temperatures. You can check to see if your lawn is alive by taking a small sample indoors. Water it and place it on a window sill. You should see some growth in two weeks time.

Last chores of the season

By now you should have completed your last watering, mowing, and fertilization of the season. If you did not keep up with watering this fall and fear the worst, dormant seeding in mid-November will be a great option. For that I would like to direct you to a couple of links. The first link is a great discussion previously published in the Yard and Garden News by Bob Mugaas, retired Extension Turfgrass Educator. Bob discusses the most important factors for dormant seeding, including: choosing the right seed, seed to soil contact, and post seeding management. The second link is from the Virtual Field Day that we held this fall. In it, Dr. Eric Watkins professor of Turfgrass Breeding and Genetics discusses your turfgrass species options for Minnesota lawns. I encourage you to consider all of the species characteristics when choosing the turf seed for your lawn.

Dormant seeding:

Turf species selection:

On the horizon: In search of a more sustainable grass

These are exciting times for sustainable lawn care in Minnesota. A $2.1 million dollar USDA grant was recently awarded to the University of Minnesota's Turfgrass Program for the improvement of fine fescues. Dr. Eric Watkins, a professor at the University of Minnesota, is the principle investigator on this project, which is a collaboration with Rutgers University and the University of Wisconsin-Madison. Intentions for this research include changing consumer habits, as well as improving the genetics of these low maintenance species. Please follow the links below for more information:


KARE 11:

Sam Bauer, Extension Turfgrass Educator

With rising economic and environmental concerns regarding the efficient use of fertilizers in urban settings, it becomes important to understand the role that late-fall fertilization plays in our lawn care program. Long-standing recommendations for late-fall nitrogen fertility involved the use of quick release nitrogen sources (urea, ammonium sulfate, others) to be applied after the last mowing of the year. The theory was that the nitrogen would be absorbed by the turfgrass roots prior to winter, but would not be utilized for growth until the following spring. While this theory seems reasonable, and generally results in a healthier lawn, the predictability of quick release nitrogen applications at this time is low.

Sam Bauer

Photo 1: U of MN grounds manager Jonathan Spitzer applies a 50/50 blend of quick release and slow release nitrogen sources to the St. Paul campus turf in late-September.

Collaborative research between the University of Minnesota and the University of Wisconsin-Madison has demonstrated that turfgrass absorption of nitrogen reduces as temperatures cool later into the fall. We refer to this as a reduction in turfgrass nitrogen use efficiency (TNUE). In climates that are conducive to a reduction in TNUE, as in the case with slow growth associated with late-fall temperatures, fertilizer applications have a greater potential to move off-site. This off-site loss is particularly concerning due to environmental and economic implications.

Consider the fact that the costs of producing nitrogen fertilizers have more than tripled in the last decade due to the rising price of fossil fuels used for nitrogen fertilizer production. Additionally, the Environmental Protection Agency has placed a 10 ppm nitrate standard on drink water. These are the driving factors for refining the late-fall nitrogen fertilizer recommendations, as we can no longer afford to make nitrogen fertilizer applications that have a high potential to move off-site.

The new recommendations can be summarized as follows:

- Make final nitrogen fertility applications no later than mid-October
- Combine quick release and slow release nitrogen sources when applying more than 0.5 pounds of nitrogen per 1000 square feet
- Only apply fertilizer to actively growing lawns, because TNUE reduces when growth is low

Phosphorus and potassium applications should always be based on soil test results. Soil testing information and submission forms can be found at the University of Minnesota Soil Testing Laboratory website:

For more detailed information regarding the use of home lawn fertilizers follow these links to a three part discussion from retired Extension Turfgrass Educator Bob Mugaas.

Understanding and Using Home Lawn Fertilizers- Part 1: The Basics

Understanding and Using Home Lawn Fertilizers- Part 2: Nitrogen

Understanding and Using Home Lawn Fertilizers- Part 3: Phosphorus and Potassium

Sam Bauer, Extension Turfgrass Educator


A resounding sigh of relief was felt over much of the state as July passed. It was the second hottest July on record in Minnesota, and the hottest in 118 years of records throughout the rest of the country. Precipitation around the state varied greatly. From record droughts in northwest and parts of southern Minnesota, to record floods in the northeast, this summer was anything but typical. Homeowners in the Twin Cities metro should feel very fortunate to not be dealing with the after-effects in these areas. Still, if you were able to sustain the quality of your lawn throughout July, it was truly a blessing.

August came and went fairly quickly with very little love from Mother Nature, almost a three inch rainfall deficit in the Twin Cities. The map below from the MNDNR State Climatology Office puts precipitation deficits into perspective across the state from July 31st to September 24th.

MNDNR Climatology

Photo 1: Precipitation Map for Minnesota

September ended with only 0.3 inches of rainfall recorded in the Twin Cities. In fact, it was the second driest September on record. Central and northeastern Minnesota suffered the worst. What implications does this have on your fall lawn care practices? I'm glad you asked.

Fall is the preferred time for many important lawn care practices. From fertilization and weed control, to cultivation and seeding, there is absolutely no better time for cool-season turfgrass maintenance in the Midwest. But this year is different. The lack of precipitation in August and September has caused many of our Kentucky bluegrass, perennial ryegrass, or fine fescue lawns to brown out and cease growing, almost a revert back to summer dormancy for those homeowners that lack the availability of adequate irrigation. In order for your lawn to recover, you will need to begin irrigating regularly. This means more than just one or two cycles, but enough water to wet the root zone sufficiently to sustain turfgrass health.


Speaking of turfgrass health, if your lawn is stressed from lack of moisture, typical fall maintenance practices that we have recommended in the past will add additional stress. In this case, we might actually see our lawn quality decline from the practice, for example: aerating.

The best advice that I can give you is to determine the growing conditions that are furthest from optimum and correct those first. If your lawn is declining from a lack of moisture, irrigate. If you've been irrigating with little turfgrass response, soil compaction may be an issue, in which case aerating would help. Has your fertility program been adequate? Are there insect or weed pressures? These are all questions to consider.
Concentrate more this fall on creating the best possible growing environment for your turfgrass, and you will reap the benefits during next year's growing season. Adding turfgrass stress to an already stressful situation will do more harm than good.


Return adequate soil moisture levels and turfgrass health before you conduct these practices.


• Aerate. While aeration is a great fall practice, it places stress on the turfgrass plant and may actually cause the lawn quality to decline.

• Dethatch or vertical mow. This process tears turfgrass leaves and crowns, and should only be conducted when the lawn is healthy.

• Spray herbicides. Systemic and contact herbicides used for weed control are more effective when weeds are actively growing.

• Fertilize with quick release nitrogen. High rates of quick release nitrogen fertilizers can have negative effects on drought-stressed turf. There is also a greater potential for environmental loss of nitrogen when the lawn is not actively growing.

• Mow too often or too low. Raising the mowing height and mowing less frequently will help encourage turfgrass recovery.


• Maintain soil moisture to promote turfgrass recovery.

• Spot seed and fertilize thin and weak areas with a high quality turfgrass seed mixture.

• Fertilize with slow release nitrogen sources and soil test to determine fertilizer requirements of phosphorus and potassium.

• Aerate when the lawns health has been restored.


Karl Foord - Extension Educator, Horticulture

Click on the link to see the video with host Dr. Mary Meyer, Professor of Horticulture

Barrenwort (Epimedium x rubrum)

Periwinkle (Vinca minor 'Dart's Blue')

Pennsylvania Sedge (Carex pensylvanica)

September Ushers in Prime Time for Home Lawn Care Activities

Bob Mugaas, UMN Extension Educator

Bob Mugaas

Late summer lawn and landscape.

The arrival of the Minnesota State Fair and its wrap-up on Labor Day weekend, mark the beginning of one of the best times of the year for initiating and renewing home lawn care activities. When it comes to repairing and rejuvenating your lawn after it has endured the stresses of another summer, avoid the temptation to also be winding down your lawn care efforts once Labor Day has passed. The main reason is that our grass plants are entering a very active period of growth triggered by a shortening of the days, cooler temperatures and usually a return to more frequent rainfall. Following are a number of brief lawn care tips that can help restore any lawn's health and vigor.

1. The middle of August through the middle of September is one of the best times of the year for lawn renovation and reseeding. Practices such as dethatching and aerifying are all best done at this time of year. Again, the primary reason for this is related to the grass plant's active period of growth and recovery during early to mid fall.

2. In addition, our soils are nice and warm from the summer heat. Warmer soil temperatures and ample moisture make this one of the best times of year to be doing some (re)seeding. Grass seed germinates and establishes more quickly increasing the chances of good winter survival. Also, because we have passed the time for many of our annual weed seeds to germinate and grow, there will be virtually no competition from annual weeds such as crabgrass, yellow foxtail, lambsquarters or common ragweed.

3. Putting down some nitrogen(N) fertilizer at the rate of one pound of N per 1000 square feet from late August through about the middle of September will be beneficial. This is the time of year when our grass plants readily absorb the nitrogen applied and use it to support various plant processes during the active fall growth period.

Bob Mugaas

Late summer early fall provides good control of common dandelion.

4. By later in the month, we are getting to the time of year when we can be most effective with herbicides at controlling those perennial broadleaf weedy plants such as dandelions, white clover, creeping Charlie and broadleaf plantain. Like our grass plants, these weedy plants are also actively growing and will actively take up and transport the weed killer throughout the plant giving better control. For example, dandelions are best treated from about mid-September to early October in the Twin Cities area. Plants will be killed this fall but the real difference will be observed next spring when there are few to no dandelions in what may have been a previously heavily infested area. However, this is not the time of year to be putting a preemergence crabgrass killer down hoping to have success next spring. Preemergence crabgrass killers are much more effective when used and applied properly in the spring.

5. One of the most common questions this time of year is, "How long into the fall should I continue to water my lawn?" The easiest answer is to continue watering so long as the plant continues to need water. In other words, if we have extended dry periods in the fall, grass plants will still need water to support active growth at this time of year. Remember that just because temperatures are cooler and days are getting shorter, soils will still dry out during extended periods of no rainfall or supplemental irrigation. It is desirable to gradually lengthen the time interval between watering to allow the soil to slightly dry before adding some water. This will help prepare the grass plants to better survive harsh winter conditions.

Likewise, these same conditions can make it easier to overwater and keep the plants too wet. Overly wet soils are very stressful for grass plants and can significantly increase certain diseases and just generally weaken the plant. As a gauge for your own lawn, check the soil moisture level periodically. If it feels damp to maybe just slightly dry and not wet and sticky that's probably about right for soil moisture during the late summer fall period.

6. At least during the month of September, mowing should continue on a regular basis maintaining a lawn height of about 2.5 to 3.0 inches. Heights can be gradually reduced back to about 2.0 to 2.5 inches by the time we get into late October. Remember that right now and for the next several weeks grass plants can take advantage of higher heights of cut by producing more food via photosynthesis due to more leaf tissue present. That also translates into very active root growth such that roots will extend deeper into the soil and in general develop a more robust root system. Both conditions aid in the uptake of water and nutrients from the soil thereby contributing to a healthier plant.

For many people, September marks the beginning of many family things like vacations ending, children going back to school, volunteer activities resuming and the like. With as busy as things can get in our family lives, try to remember this is also a time of new beginnings and renewal for our grass plants and lawns. Providing some additional nitrogen nutrition, watering during dry periods, mowing regularly and doing some reseeding to those injured and damaged areas of the lawn are all perfect activities for this time of year. In addition, restoring and maintaining a healthy lawn in the fall significantly contributes to better winter survival and a healthier lawn next spring.

For more information on any of the above topics see the lawn section on the University of Minnesota's website under Garden. You can also find lots of information about Minnesota home lawn care on the Sustainable Urban Landscape Information Series website. Got an unfamiliar weed in your lawn? Check out our on-line weed identification guide at "Is this Plant a Weed?" from the Garden link mentioned above. You can also find out how to control many of the common lawn weeds on that site as well.

Kathy Zuzek

Photo 1: White spruce symptoms being associated with Imprelis herbicide damage.

Bob Mugaas and Kathy Zuzek, UMN Extension Educators

Reports continue to be received regarding herbicide injury to white spruces, white pines and a variety of other woody and herbaceous landscape plants. The herbicide in question is Dupont's Imprelis, whose active ingredient is aminocyclopyrachlor. It belongs to a new class of broadleaf weed control herbicides which are similar, but not identical, to existing products such as triclopyr or fluroxypyr, both commonly used for control of more difficult lawn weeds such as clover and creeping Charlie.

Kathy Zuzek

Photo 2: White pine symptoms being associated with Imprelis herbicide damage.

Aminocyclopyrachlor is classified as a synthetic auxin or growth regulator type of herbicide. In susceptible plants, the herbicide produces characteristic twisting and curling of the foliage ultimately leading to plant death. Most of us have probably observed these effects on dandelions that we have treated with home lawn weed control products containing 2,4-D and/or dicamba, two other growth regulator type of herbicides but with different chemistries than aminocyclopyrachlor.

Bob Mugaas

Photo 3: Additional symptoms on white spruce near top of tree.

Dupont introduced Imprelis to the professional turfgrass management industry this year. It has a track record from various research efforts of providing good to excellent control of some of the more difficult to control lawn weeds (e.g., creeping Charlie, wild violets, clover and Canada thistle). However, what is also being observed in many of the northeastern and midwestern states is significant, unanticipated damage to certain spruce species and white pines (Photos 1 and 2) with a scattering of injury reported on other conifers and broadleaf plants.

Bob Mugaas

Photo 4: Less severe damage on white spruce shoots and needles.

When initial reports started showing up around the end of May into June from the northeastern states, the two conifer species most commonly showing injury were Norway spruce (Picea abies) and white pine (Pinus strobus). When injury reports began coming into our own Department of Agriculture and Extension a short time later, most of the injury was on white spruce (Picea glauca), (Photo 3), including its geographical variety Black Hills spruce and white pine, again with a scattering of injury to other conifer and broadleaf plants. Colorado blue spruce (Picea pungens) has also shown some injury but generally much less dramatic than seen on white spruce or white pine.

Kathy Zuzek

Photo 5: Twisting and distortion of white pine shoots and needles.

As one might imagine, this kind of injury has created enormous concern among homeowners and professional lawn care applicators alike. The two biggest questions on everyone's mind is "Will the trees survive?" and if so, "Will their aesthetic landscape qualities be completely ruined and hence still need to be replaced?" Unfortunately, in all but the most severely damaged trees, it's a bit of a wait-and-see situation. In this area, the white spruce and white pine trees observed so far show damage only on the new or current year's growth, but, that is where new buds are formed for next year's growth (Photos 4 and 5). If this year's growth is lost, no new buds will have been formed and next year's growth may be sporadic around the tree and at worst the tree may still end up dying.

Kathy Zuzek

Photo 6: Normal shoot, needle and bud set in spruce.

However, in some cases, the new growth appears to be setting new buds somewhat normally even though this year's growth itself is often twisted and distorted. For comparison, see Picture 6 for what normal bud set and shoot growth should look like in spruce. If affected shoots remain alive and mature normally the rest of this season, next year's growth may very well be O.K. even though this year's twisted and distorted shoots will still be evident. In more severe instances where the new shoots along with the needles have already begun to turn brown and there appears to be little or no bud development occurring, (Photo 7) shoots are unlikely to survive. Where these symptoms are widespread on the tree, if it does survive, any remaining landscape value would appear to be unlikely. (Photo 8).

Bob Mugaas

Photo 7: Severe and likely permanent damage to new white spruce shoots and needles.

A third question on many people's minds is "Is there anything I can do to help save the tree or reduce the damage?" At present there are varying opinions as to what the best cultural practices are to minimize or reduce the impact of current injury as well as reduce the probability of further injury. For now, it seems that preventing any additional stress to the trees would be beneficial. For example, watering to avoid additional drought stress on the tree, while at the same time being careful not to overwater the trees, would be prudent.

Kathy Zuzek

Photo 8: Entire white spruce with nearly all new growth severely affected.

Because much is still unknown about this unfolding and expanding situation, the Minnesota Department of Agriculture is currently collecting information from University of Minnesota Extension, DuPont, EPA, commercial lawn care applicators, and other state departments of agriculture to assess the scope of this issue. You can visit the Imprelis page on the MDA's website. See their official statement on the situation at this time and how to contact them with damage reports. Also, there is currently a good summary article by Dr. Peter Landschoot from Penn State University regarding the characteristics of this herbicide and the impacts they're seeing on affected trees. You can access it via Penn State University Extension.

As symptoms continue to develop and further assessment of survival is documented there will likely be other articles on this situation, I'm sure. Stay tuned!

Early June Home Lawn Care Tips

Bob Mugaas, UMN Extension Educator

Picture 1(2).JPG

Photo 1: Newly emerging crabgrass seedlings. Bob Mugaas.

1. In many areas of the state, crabgrass, along with other warm season annual grasses are or will soon be germinating in lawns. See Picture 1. Once crabgrass has emerged from the ground, control strategies need to be changed. Herbicides directed at controlling crabgrass above ground are known as postemergence products. Be sure to select those products that are specific to visible, actively growing crabgrass plants only. Those products labeled as grass killers are usually designed to kill all kinds of grasses, including lawn grasses, not just crabgrass. Products sold as broadleaf weed and grass killers may or may not be safe for use on lawns. Be sure to read the product label carefully as to whether or not it is a product that is safe for use on lawn grasses. When treating crabgrass after it has emerged from the ground, be sure that the desirable lawn grasses are not under any kind of heat and/or drought stress as you can sometimes cause temporary yellowing. Under severe stress, permanent injury can also occur to our lawn grasses. As with most weed control options, treating the plants while they are small and tender is generally more effective than trying to control larger, more mature plants.

Picture 2(2).JPG

Photo 2: An easier to control or remove young lambsquarter weed
Bob Mugaas.

2. By early to mid-June, many of our annual broadleaf lawn weeds will also be starting to germinate. One of the best times for controlling these weeds is in this early growth stage before they have started to mature and initiate flowering. Examples of our common annual broadleaf weeds include prostrate or spotted spurge, erect and prostrate knotweed, lambsquarter, redroot pigweed and purslane. See Picture 2. The clover like plant, black medic as well as yellow woodsorrel are usually considered annuals although some plants may overwinter and behave like a biennial or short lived perennial. Taking a few minutes to walk your lawn in order to determine when some of these weeds may be germinating allows one to easily remove them by hand and/or treat them with an herbicide. Remember, removing and/or treating plants with an herbicide is much more efficient when they are small, even at the lower application rates stated on the product label. For more weed identification help and possible control options for lawn weeds see our 'Is this Plant a Weed?" section on our Extension website:

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Photo 3: Raise mowing heights to encourage larger, deeper grass root systems.
Bob Mugaas.

3. Since this is the time of year when many of our weed seeds are germinating, including those of crabgrass, it is generally best to avoid lawn care operations such as dethatching or core aerating. These operations disrupt the surface of the soil and can bring additional weed seeds into a more favorable environment for germination and growth, hence creating additional competition for our lawn grasses. For that reason, it is best to wait until late summer or early fall to resume these operations. However, be sure to leave at least four to six weeks of good growing conditions for the grass to fully recover from this injury before consistently cold weather arrives.

4. Along with our cooler than normal temperatures for much of the spring, many areas of the state have also received adequate to abundant amounts of rainfall. Those cooler temperatures and ample moisture supplies have encouraged vigorous, lush growth of our lawn grasses. Vigorous growth and rainfall will have likely depleted at least some of the available nitrogen in the soil making less available for plant growth. Therefore, most lawns will benefit from an additional ½ pound of nitrogen per 1000 square feet applied in the early to middle part of June. This will help replenish the supply of N used by the plant or lost due to leaching or returning to the atmosphere in a gaseous form through a process known as volatilization. This is about ½ the normal amount of nitrogen applied per application. On the other hand, too much nitrogen encourages more rapid and excessive growth that can compromise the overall health of the grass plant going into the summer months.

5. Lawn grasses will usually have better stress tolerance when they are mowed higher from the middle of spring through early fall. See Picture 3. Higher heights of cut usually mean at or above 2.5 inches for most lawn grasses. This helps encourage deeper, more robust root systems capable of extracting water and nutrients from a greater soil volume. Access to more soil moisture and nutrients increases the plant's capacity to tolerate and survive the warmer, drier conditions often experienced late spring through the summer months.

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Photo 4: Shorter than expected mowing height due to softer ground conditions. See text for more explanation. Bob Mugaas.

6. While most walk-behind rotary mowers adjust mowing heights by resetting the four wheels to the desired height, it is occasionally a good idea to see how close that setting really is to the actual height of cut. The easiest way to do this is to simply take a ruler and gently push it through the turfgrass canopy until it rests firmly on the lawn/ground surface. Then look across the grass plants just in front of the ruler and see what the height is. For example, if the ground is firm then mower wheels will ride higher and consequently the height setting will more closely approximate the actual cutting height. However, where the ground is soft or there is a significant thatch layer present, the wheels will sink more deeply into the lawn and hence the mowing height is actually less than the wheel settings would indicate. In fact, where there is significant thatch present mower wheels can ride so much lower that the lawn surface between the wheels is actually scalped. See Picture 4. Remember to take the time to adjust your mower correctly, periodically verify that the mower height settings are actually providing the desired height of cut, and always mow with a sharp blade.

7. With so many yard and garden chores needing to be completed during a typical Minnesota May and June, it is very easy to overlook the water needs of our lawn grasses. However, it's important to remember that May and June are very active growth months for our lawn grasses. While much of the growth is directed at producing flower stems, our bluegrasses and perennial ryegrasses will grow much better with ample supplies of water during this period. An 'ample supply' usually means that the lawn receives about ¾ to 1.0 inch every seven to ten days including rainfall. See the May 15, 2011 Yard and Garden News blog for more information on Lawn watering practices that encourage healthy lawns and help protect water resources.

Bob Mugaas, UMN Extension Educator, and Dr. Brian Horgan, Turfgrass Management, UMN Department of Horticultural Science

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Photo 1: Proper watering benefits all landscape plants, especially lawns. Bob Mugaas.

While water is essential for all plant growth, it is not always uniformly available or distributed when and where the plant needs it. Therefore, supplemental water is often needed to sustain and support healthy plant growth whether it's vegetable plants, annual flowers, trees and shrubs or lawn grasses. Picture 1. For most of us, that means getting out sprinklers and hoses and watering on occasion. There are also automated systems available to aid in the distribution and convenience of supplying supplemental water to lawns. Following are some watering practices beneficial to lawns that can help minimize unintended, negative environmental impacts.

Water friendly lawn care practices anyone can implement

  • During the hot and dry summer months, lawns will need about an inch of water per week including rainfall to remain green and growing. One inch of water per week may be sufficient for two weeks or longer during the cooler periods of spring and fall. Always remember to factor in the amount of water received via rainfall so as not to be applying more water than the plant needs or can use.

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    Photo 2: Unhealthy ponding of water on lawn surface. Bob Mugaas.

  • Adjusting watering practices seasonally is necessary. In the spring and fall when roots are active and deeper in the soil, larger amounts of water can be applied per application but with longer periods of time between watering. In summer, more frequent watering is necessary due to shallower rooting depths. Shallow but more frequent application of water DOES NOT MEAN that the soils should remain saturated with water. (See the following section on the various problems associated with waterlogged lawns and soils.) Some soil drying between watering is beneficial for the plant. Slight moisture stress experienced by the plant will encourage rooting.
  • When irrigating, avoid excessive amounts of water that may cause puddles on the surface of heavier clay soils. See Picture 2. Moreover, too much irrigation on sandy soils leads to the water moving past the root system increasing the likelihood that nutrients being carried with the water will potentially contaminate groundwater.

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    Photo 3: Mowing higher encourages deeper rooting. Karen Vidmar.

  • Water early in the morning when temperatures are cool and winds are light. This puts more water into the lawn for grass plant use and less lost to evaporation.

  • Mow grass plants higher (3.0 to 3.5 inches) especially during the summer to encourage a deeper, more robust root system. See Picture 3. Deeper roots can access greater supplies of water and nutrients in the soil. In other words, lawns mowed higher will better tolerate the warm and dry conditions of summer. When supplemental water is needed, it is often on a less frequent basis ultimately conserving water.

  • Core aerifying compacted soils will: improve water infiltration, reduce runoff, increase rooting and access to soil nutrient and water reserves.

  • Take advantage of irrigation system rain sensors and/or soil moisture sensors. These will prevent automatic systems from turning on during periods of rain or when there is already enough moisture in the soil.

Be careful not to keep your soil too wet!
Picture 4.JPG

Photo 4: Creeping bentgrass taking over in an excessively moist Kentucky bluegrass lawn. Bob Mugaas.

Never allow the surface soil to remain water saturated (i.e., waterlogged), even for short periods of time. See Picture 2. Healthy grass root systems need soils with equal parts water and air. Air in the soil pore space is required for both nutrient and water uptake. Too much water forces air out of the pore spaces creating a waterlogged condition. This yields root dieback and a shallow root system making plants more vulnerable to a number of serious plant stresses and diseases.

Other issues and problems associated with overly wet soils.

  • Excessively wet soils can contribute to undesirable development of thatch (greater than ¾ inch or more). Excessive thatch is associated with poor stress tolerance and increased disease and insect problems.

  • Soils that remain wet are often invaded by grassy weeds, which can be difficult to control once established in a home lawn. Examples include annual bluegrass, rough bluegrass, creeping bentgrass and yellow nutsedge. See Picture 4. Also, moist shady areas can be invaded by moss. This is another difficult plant to control unless the environmental conditions can be changed to not favor moss growth. Conversely, lawns that are allowed to dry somewhat between watering rarely have even minimal problems with any of these weeds.
  • Research studies have shown that when additional water is applied or falls on already waterlogged soils, there will be an increase in the amount of runoff volume and potential nutrient loss under those conditions.

  • During warm summer conditions, waterlogged soils can significantly increase the loss of fertilizer nitrogen back to the atmosphere in the form of nitrogen gas. Likewise nitrogen carried in water moving down through the soil past the plant's root system can also be accelerated. In either case, this can end up wasting the fertilizer applied and potentially contaminate ground water.

For more information regarding proper lawn watering practices, check out the Lawn Watering chapter of the Sustainable Urban Landscape Information Series at the U of MN Extension website.

Bob Mugaas, UMN Extension Educator


Photo 1: Steps for properly taking a soil test. Karen Vidmar, University of Minnesota.

Over the last couple of articles we have explored how to better understand the sometimes bewildering array of lawn fertilizers available and make appropriate choices for one's own lawn as well as the large and diverse role that the nutrient nitrogen plays in the life of lawn grasses. Part III, the final section of this three-part series, will turn attention back to the nutrients phosphorus (P) and potassium (K) and the important roles they play in turfgrass health. Since determining the amount of P and K in a container of lawn fertilizer was thoroughly discussed in the first article of this series, this last article will focus on the importance of P in K in turfgrass health and their application as a component of lawn fertilizers. Before beginning, remember that the best way to determine the amount of P and K in your soil is to have a reliable soil test done such as that performed by the University of Minnesota Soil Testing Lab. Collecting the soil to test properly is important for accurate soil test results. See Picture 1.

Turfgrasses and the important role of phosphorus(P) in plant health.

Phosphorus is an important component of many different plant molecules and compounds responsible for promoting healthy turfgrass growth. In fact, without ample P, normal healthy growth is not even possible. Some of its more important roles include those related to the storage and transfer of energy within the plant, promotion of healthy, well developed root systems, proper formation of plant cell membranes and, it is an important component of the cell's genetic material including its DNA.

In addition to its important roles within the plant, a critical component to understanding the use of phosphorus fertilizer is how it behaves in the soil. That is, phosphorus moves very little in the soil with most of it being bound tightly to soil particles. As a result, phosphorus does not move into the soil water solution as easily as other nutrients (e.g., nitrogen). That's both good news and bad news for the grass plant. The good news is that P is much less likely to move down through the soil via leaching and be lost as a plant nutrient. Hence, its supply in the soil is relatively stable. The bad news is that with such little movement in the soil it can make it more difficult for the plant to obtain sufficient supplies of P to support healthy growth.

Fortunately, healthy, actively growing lawn grasses have an extensive, dense, fibrous root system that makes them relatively efficient as extracting P from the soil compared to many other plants. For this reason, the application of supplemental P via fertilizer to an established, mature stand of turfgrass is usually unnecessary or needed in only very small amounts. Again, this is not because our grass plants require less P for growth than other plants. Rather, they are just more efficient at extracting available P from the existing soil. It should also be apparent that when our lawn grasses have shallow restricted root systems, such as in compacted or waterlogged soils, they do not have as much access to potential soil reserves of phosphorus and hence supplemental applications of P via a fertilizer may be necessary.

Additional phosphorus at establishment is beneficial


Photo 2: Available soil phosphorus is needed for these young developing grass plants. Bob Mugaas, U of MN Extension.

Application of a phosphorus fertilizer, often purchased as a lawn starter fertilizer, is recommended at the time of establishing a new lawn or completely renovating an existing lawn. In this instance, the additional phosphorus is applied and lightly incorporated into the soil surface where it is more readily available to the very young, developing grass root system. See Photo 2. This aids in the promotion of vigorous seedling growth and quicker establishment. Once established and the grass plants have developed a deeper much more extensive root system, the application of supplemental phosphorus fertilizer can be reduced or even eliminated (at least temporarily) depending on existing soil P levels as determined by a soil test.

Fertilizer phosphorus and water quality issues

While loss of phosphorus from a lawn via leaching is considered to be very low, losses via runoff and soil erosion can occur and can create pollution problems for nearby lakes and rivers receiving stormwater runoff. Once in a lake, the additional P, even in very small amounts, can stimulate rapid and excessive algae growth. In turn, these 'algae blooms' as they are called can significantly reduce water quality for many different uses and negatively impact fish and other lake life.

The Minnesota Phosphorus Fertilizer Law:

Because of this concern for excessive phosphorus in lakes and rivers from fertilizer, the Minnesota legislature passed a statewide law that restricts the application of phosphorus fertilizer to established lawns and other turfgrass areas. The law states that fertilizers used on lawns will be restricted to 0% phosphate (P2O5) content. Exceptions include application at establishment, either by seeding or sodding, and then only during the first year of establishment. Applications can also be done when a soil or tissue test shows a need for P. In those cases, lawn fertilizers with P can be used. More detail pertaining to the law and the penalties than can be applied is found in Chapter 18C.60 of Minnesota Statues. Because of this law, soil testing becomes even more important for managing applications of phosphorus to turfgrass.

Recent U of MN research sheds additional light on the potential for lawn phosphorus losses.

Recently completed research at the U of MN, clearly showed that neglected lawns (i.e., those receiving no additional fertilizer), became thin and weed infested over the course of the study and contributed more runoff volume and more phosphorus loss during the growing season than those receiving sufficient levels of fertilizer to maintain good turfgrass density and active growth. In addition, there was essentially no difference in the amount of runoff volume or phosphorus loss between those lawn plots receiving nitrogen and potassium only and those receiving nitrogen, a low rate of phosphorus (1.0 pound of P annually) and potassium. Hence, where background levels of soil P are high on an established healthy stand of grass, there does not appear to be any significant decline in plant health or vigor, when P is no longer being added via fertilizer. In general, that result would support one of the law's assumptions that additional P is not necessary for healthy turfgrass when ample levels already exist in the soil. Likewise, neglecting a lawn entirely by applying no additional fertilizer to maintain plant health and density would not be a good practice.

For those of you interested in more details and results from this study, there is a link to the complete final report of this study in the Phosphorus section in the Understanding and Using Lawn Fertilizers chapter of the Home Lawn Care section of the Sustainable Urban Landscape and Information Series (SULIS). The U of MN Extension publication entitled Preventing Pollution from Lawn and Garden Fertilizers provides additional information on the responsible use of fertilizers to protect water quality.

Turfgrasses and the important role of potassium (K) in plant health.

Even though grass plants contain rather large amounts of the nutrient potassium there is still much we don't know about the biological role and activity of potassium in the plant. Potassium is important in the synthesis of many plant components and in the regulation of many physiological processes including the efficient use of nitrogen. While potassium is involved in many of these activities, it is usually not an integral part of the final product produced. Some of those plant processes where potassium is involved but not part of the end product include the formation of carbohydrates and the photosynthetic process, activation of various enzymes that in turn control other plant processes and, aids in the formation of plant proteins.

Where soil potassium levels are low and plant deficiencies exist there is often a reported increase in the incidence of turfgrass diseases and reduced tolerance to environmental stress. However, the visible, field detection of a potassium deficiency can be difficult at best. While research continues, our understanding of the biology and specific roles that potassium plays in the plant remains rather elusive.

Potassium is held on the surfaces of soil particles and moves little in most soils, though it can gradually move out of the root zone in very sandy soils. Its movement in soil is often considered to be between that of nitrogen, which is very mobile, and that of phosphorus, which is very immobile. Where soils are high in native potassium, supplemental potassium fertilization may be unnecessary; however, where soils are low in native potassium, supplemental applications can be very important. However, an application of additional potassium does not necessarily create obvious visible symptoms as one might associate with the nutrient nitrogen. Again, soil tests are essential to determine the potassium level of a soil and to develop a potassium fertility program.


Photo 3: Healthy, dense lawns can help protect water resources. University of MN Extension.

Concluding remarks

It is hoped that this series of three articles beginning with the March 1, Yard and Garden News issue followed by the April 1 issue and concluding with this one has provided at least some basic insight into the importance of the three major nutrients contained in most lawn fertilizers to a healthy, vigorous lawn. Selecting an appropriate fertilizer and applying it correctly may just be one of the more important things you can do for your lawn and protect the environment at the same time.

Bob Mugaas, UMN Extension Educator

This is the second article of a three part series on Understanding and Using Home Lawn Fertilizers. This article will focus attention on the nutrient nitrogen, why it gets so much emphasis in lawn care and, the roles that it plays in maintaining a healthy, vigorous lawn. As we begin this article, it is important to remember that while other nutrients such as phosphorus and potassium are important for healthy lawns, it is the nutrient nitrogen upon which nearly all general recommendations for home lawn fertilizer applications are based.

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Photo 1: Healthy, dense lawn promoted by proper use of N fertilizers. Bob Mugaas.

Grass plant absorption of nitrogen and its impacts on grass growth
Nitrogen (N) is the mineral element used in the largest quantity by our grass plants. It is absorbed primarily from the soil by the plant's root system. However, nitrogen is not absorbed by the plant in its elemental form (N). The two most commonly absorbed forms are the nitrate ion (NO3-) in which N is combined with oxygen(O) and contains a single negative charge on the molecule and the ammonium ion (NH4+) in which N is combined with hydrogen(H) and contains a single positive charge on the molecule. Of these two forms, the nitrate form is absorbed in the largest quantity by the plant root system.

Once N is inside the plant it becomes an integral part of many other plant molecules and processes. Among those various roles, one of its most important is in stimulating shoot growth which aids in spring green up and helps promote recovery from injury and environmental stresses. Interestingly, shoot growth is often stimulated at the expense of root growth. Thus, lower, more modest use of nitrogen fertilizer, especially in the spring of the year, is actually healthier for the plant as shoot growth will be more in balance with root growth. In turn, the plant will be in a healthier condition and better able to survive the more stressful summer growing conditions. See Picture 1.

Nitrogen also plays an important role in the production of the green pigment known as chlorophyll which in turn is responsible for producing the green color in grass. This is why you often find yourself mowing more frequently and observing a deeper green color to your grass following a nitrogen fertilizer application. After a few days following a nitrogen fertilizer application, any lawn areas that were skipped or missed will also be very evident. Non-fertilized areas or skips will be distinctly lighter green compared to those areas receiving fertilizer. Depending on the degree of misapplication, it may be quite embarrassing as well.

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Photo 2, Bob Mugaas.

Nitrogen needs can vary by grass species
While nitrogen is used by grass plants in larger quantities than other nutrients, there is some variability as to how much is needed among the different lawn grass species. For example, Kentucky bluegrass and perennial ryegrass require larger amounts of N than the fine fescues to remain healthy and vigorous. This is one of the main reasons why the fine fescues are the plant materials of choice when it comes to implementing low input lawn care programs or where no-mow plantings are desired. Under otherwise favorable growing conditions, fine fescues can get by with as little as 1# or even less of actual N per 1000 ft2 per year.

Picture 2 illustrates the difference in texture between Kentucky bluegrass and the fine fescues. If your lawn is dominated by the finer textured fine fescue grasses, you can likely reduce the amount of nitrogen applied as noted above and still expect to maintain acceptable or better lawn quality.

Why the need for supplemental nitrogen

While grass plants are moderate to high users of nitrogen depending on species, it is not the only fate of nitrogen in our soils. There are two other soil related processes that play an important role in how much nitrogen is available for plant growth during the growing season. First, the nitrate form of nitrogen can easily be carried along with the vertical movement of water down through the soil. This is the process known as leaching. It effectively moves nitrate nitrogen beyond the root systems of our grass plants and now has the potential to continue downward through the soil and potentially pollute ground water supplies. Second, nitrate nitrogen can also be converted to nitrogen gas (N2) through a process known as denitrification. This most commonly occurs during warm, wet soil conditions.

The end result of these three major soil nitrogen losses along with losses from a few other minor soil processes is that our soils often lack the necessary amount of nitrogen needed to support healthy, vigorous grass growth at all times during the growing season. Hence, there is often a need to supplement our soils with some additional nitrogen containing fertilizer in order to sustain a healthy turfgrass system throughout the year.

Natural nitrogen inputs to a lawn
Before delving into nitrogen fertilizers, it is important to remember that fertilizer is not the only means by which our lawns receive supplemental N inputs. For example, as organic matter is continually being decomposed by the soil microbes, nutrients, including plant available nitrogen, are released back to the soil for use by the grass plants or perhaps reused (and rereleased) by other microorganisms. When soil test results indicate organic matter levels of 3.1% or higher, about 0.5 pounds (or slightly more) of actual nitrogen per 1000 ft2 can be returned to the lawn annually.

Grass clippings generated during regular mowing and left on the lawn over the entire season will supplement the lawn with the equivalent of about one complete fertilizer application annually or about 1 pound of actual N per 1000 ft2 per year. Under very low maintenance situations, including no irrigation, these natural supplies of N may be sufficient to sustain the turfgrass. However, some (0.5 - 1.0 #N per 1000 ft2) supplemental nitrogen will usually be necessary to sustain an acceptable turfgrass stand having at least medium green color and sufficient density to completely cover the soil surface.

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Photo 3: Necrotic ringspot disease on Kentucky bluegrass. Bob Mugaas.

When there is too much nitrogen
Over abundance or deficiency of available nitrogen are both problematic for grass plants. Excessive levels of nitrogen:
1) stimulate rapid shoot growth while slowing down root growth and increasing the need for more frequent mowing; 2) deplete the plant's carbohydrate reserves more rapidly, which in turn can result in less stress tolerance and slower recovery from any injury to the plant; 3) result in thinner, more succulent leaf tissue, which increases moisture loss and therefore creates a greater need for water; 4) can predispose the plant to greater insect and disease problems; (Picture 3 illustrates Necrotic Ring Spot disease on Kentucky bluegrass; a disease often associated with excessive nitrogen fertilizer applications.); 5) contribute to more rapid and excessive thatch development; 6) leach through the soil beyond the root system potentially polluting ground water resources when not used by the grass plant.

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Photo 4: Crown rust on Kentucky bluegrass. Bob Mugaas.

When there isn't enough nitrogen

On the other hand, a deficiency of available nitrogen results in: 1) slower grass plant growth; 2) paler green color thus decreasing photosynthetic capacity and therefore food production; 3) slower recovery from injury thus decreasing traffic and wear tolerance; 4) increased susceptibility to crown rust, red thread and dollar spot diseases; (Picture 4 illustrates crown rust on Kentucky bluegrass.); 5) decreased tolerance to environmental stresses such as drought conditions and/or high temperatures; 6) decreased lawn density thus opening the door for increased weed invasion and decreased ability to both reduce the amount of runoff as well as slow the velocity of runoff water from the site.

A brief overview of forms and sources of N fertilizer:

While a University of Minnesota soil test report can be very helpful in determining what your lawn needs, it doesn't measure the amount of nitrogen actually in the soil as part of a standard soil test. Because of the various ongoing and ever changing nitrogen losses described above, a nitrogen value won't be very helpful. In other words, a measured N level today will not likely be the same a week from now or even in a few days from now depending on weather conditions, grass growth and cultural practices being carried out. Nonetheless, the soil test report does consider the various forms of nitrogen losses and natural inputs. Thus, a soil test report will suggest a nitrogen application program based on soil test results and information provided by the user at the time the soil sample was submitted.

Quick release vs. slow release N sources. There are many sources and formulations of nitrogen found in lawn fertilizers. However, those sources can be broken up in to slow release sources (water insoluble nitrogen) or quick release sources (water soluble nitrogen). In the latter, the fertilizer is readily soluble in water and, once dissolved, the nitrogen is immediately available for grass plants to take up and use. Common examples of quick release sources include ammonium sulfate, ammoniacal nitrogen and urea. As a result, grass plants green up very quickly and grow vigorously (sometimes too much so) for a relatively short period of time following an application of quick release nitrogen.

An over application of quick release nitrogen and the accompanying excessively lush grass growth also increases the need for more moisture and more frequent mowing and can make the lawn more susceptible to certain diseases, insect problems and environmental stresses. In order to avoid this situation, it is highly recommended that quick release nitrogen fertilizer be applied at no more than one pound of actual N per 1000 2 of lawn per application.

In contrast to the rapid green up and rapid growth rate resulting from quick release sources of N, slow release sources result in a slower rate of green-up and growth. In addition, they can provide a longer period of sustained nitrogen release to the lawn. This extends the length of time the grass exhibits a healthy green color and sustains a more uniform, but slower growth rate. For these two reasons, it is also likely that the time between fertilizer applications will be lengthened and may even reduce the need for nitrogen fertilizer applied in a growing season.

Organic, synthetic organic and inorganic sources. Slow release sources can originate from natural sources such as those produced from plant or animal processing byproducts or be synthetically manufactured. The former are known as natural organic nitrogen sources while the latter are known as synthetic organic nitrogen sources. The usage of the word organic in this case simply means that the products contain the element carbon (C) in their molecular structure(s). When carbon is absent from the fertilizer molecule, they are known as inorganic fertilizers.

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Photo 5: Well-planned shoreline landscape including a healthy lawn area. Brad Pedersen.

Most of the quick release fertilizers are inorganic while slow release fertilizers are mostly organic in origin. The one notable exception is the fertilizer material known as urea. It does contain carbon in its molecular structure and therefore is considered an organic material but it reacts like a quick release nitrogen source when used in a lawn fertilizer. Urea is often the starting point for many of our synthetic organic nitrogen sources used in lawn fertilizers. These products are produced by either further chemically reacting the urea such as in the case of producing methylene urea or coating the urea such as in the case of sulfur coated or polymer coated urea. Both methylene urea and sulfur coated urea are commonly available in homeowner lawn fertilizers.

Slow release fertilizers and water quality impacts. There are also positive water quality implications when using slow release sources of N. Lawns, landscape plantings and shorelines can be compatible partners in helping to protect water resources. See Picture 5. Using slow release fertilizers can be an important tool in managing our lawns to protect water quality. Since smaller amounts of N are released over a longer period of time, grass plants have a greater chance of taking up and using the N before it potentially leaches through the soil and has a chance to contaminate ground and/or surface water resources. Because the nitrogen is released more slowly, slightly higher rates of fertilizer can be applied. As always however, be sure to follow the directions on the fertilizer container for proper spreader settings and application rates.

For more information

For a comprehensive listing of nitrogen sources and a more thorough discussion on when and how to correctly apply lawn fertilizers including calibrating a lawn fertilizer spreader for accurate application, see the Home Lawn Care Chapter on Understanding and Using Home Lawn Fertilizers in the Sustainable Urban Landscape Information Series website.

In summary
Nitrogen is an important element in sustaining normal, healthy grass plant growth and aiding recovery from injury. Used wisely and applied at appropriate times of the year, the likelihood of creating adverse effects to the lawn or the surrounding environment will be minimal.

Understanding and Using Home Lawn Fertilizers

Bob Mugaas, UMN Extension Educator

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Photo 1: Applying lawn fertilizer using a rotary spreader.

While it may only be March 1 and there is still plenty of snow covering the ground, in a few short weeks our attention will be turning to taking care of our lawns and gardens for another year. One of the spring activities that many homeowners focus on is getting their lawns off to a healthy, vigorous start; an activity that usually means applying some fertilizer to the lawn. Appealing to that desire is the rather large array of home lawn fertilizers available at local garden and home improvement centers. Frequently, that leaves the homeowner asking the question, "Which one should I buy?" or perhaps even asking the question, "Do I really need to fertilize my lawn at all?"

Over the next three months and beginning with this issue, the emphasis of this lawn care section will be on information to better understand the basics of lawn fertilizer packaging. In turn, that should help with the decision about which one to buy and some tips on getting the most from that fertilizer product.

Plant Nutrient Needs


Photo 2. The basics of photosynthesis.

Before launching into fertilizer product labeling, it's important to review why we would want to fertilize our lawn in the first place. Grass plants growing in our lawn are no different than any other green plant in that through the process of photosynthesis they manufacture all of their own needed food. See Picture 2. Biologically, we call them autotrophs. That is, we don't 'feed' out plants directly they make what they need for growth using elements or nutrients obtained from the soil or atmosphere. The three elements needed by the grass plant in the largest quantity are carbon (C), Hydrogen (H) and Oxygen (O); all of which are obtained from the air or water.

Beyond those three, the elements needed in the largest quantity to support healthy grass growth are nitrogen (N), phosphorus (P) and potassium (K); the majority of which are taken up from the soil by the root system. These three are known as primary macronutrients. In addition to these primary macronutrients, there are considered to be about 10 or 11 other essential nutrients to support healthy growth. These too, are all extracted by from the soil by plant roots. However, it is the primary macronutrients of N, P and K that are often insufficient in soils to sustain and support healthy grass growth. Hence, they often need to be supplemented in the form of fertilizers to provide an ongoing supply of these nutrients throughout the growing season.

Soil Testing to Know What's Needed

The only reliable way to determine what may be needed in the way of nutrition is to take a soil test from the lawn. Soil samples taken or sent to the University of Minnesota Soil Testing Lab for analysis will provide results regarding soil pH, organic matter content, an approximation of soil texture and the amount of available P and K present. They will also provide a basic interpretation of these results along with recommendations for what, if any, fertilizer might be needed for the lawn.

It is beyond the scope of this article to go into the details of taking a soil test or interpreting the results. However, additional information about taking a soil test can be found at the Soil Testing Lab's website . Additional information about interpreting soil test results can be found in the Extension publication Soil Test Interpretations and Fertilizer Management for Lawns, Turf, Gardens, and Landscape Plants

Remember Minnesota's phosphorus law!

Taking a soil test is always a good first step to determine what one might be looking for in the way of a lawn fertilizer. It is especially important in Minnesota as we have a state law that restricts the application of any fertilizer containing phosphorus to lawns without a soil test that indicates a need for additional phosphorus or a new lawn is being established, either by seeding or sodding, when additional phosphorus can be added to aid in the early growth and establishment of that lawn. Thus, without either of those two conditions being met, it is against Minnesota law to apply any fertilizer containing phosphorus to an existing, established lawn.

So, what's in that lawn fertilizer bag anyway?

When looking at a lawn fertilizer bag, the most common container for lawn fertilizers, there will always be three numbers present that state, from left to right, the amount of nitrogen, phosphorus and potassium contained in the bag. This specific ratio of N-P-K is known as the fertilizer analysis. For example, a bag of lawn fertilizer with the analysis of 25-5-15 would be 25% N - 5% P - 15% K. This is also known as the guaranteed minimum analysis as the fertilizer bag cannot contain any less than the percentages stated on the bag for the respective nutrients. Because this is a guaranteed minimum analysis, by law the bag could contain more than that stated but cannot be less. This fertilizer analysis is a percentage by weight basis. That is, if a bag of fertilizer with the above analysis weighed 50 pounds, then it would contain 12.5# N (50 x 0.25), 2.5# P (50 x 0.05) and 7.5#K (50 x 0.15) for a total of 22.5# of nutrients in this 50# bag of fertilizer.

The difference between the amount of nutrients contained in the bag and the total weight of the bag is largely attributed to the weight of the carrier. That is, the material used to bind to the nutrient or 'carry' them such that it can be applied using various types of spreaders. Frequently, these materials are in the form of dry granules that help disperse the fertilizer uniformly across a lawn surface when applied through a spreader.

The fertilizer analysis gives the percentages of N, phosphate (P2O5) and potash (K2O) contained in the bag on weight basis. The percent nitrogen is considered to be the actual amount of nitrogen contained in the bag while phosphorus and potassium are given in their oxide forms (i.e., they are combined with oxygen). For example, the element phosphorus only makes up 44% of the molecular mass of P2O5. Thus, in order to determine the amount of actual phosphorus contained in the bag we must multiply the percent phosphate in the fertilizer bag by 0.44. From our example above, the 5% phosphate equates to 2.2% or 1.1 pounds of actual elemental phosphorus in our 50# bag. Likewise, the element potassium makes up 83% of the molecular mass of the K2O molecule. Thus, in our example above, we would multiply the 15% by 0.83 to determine the amount of actual K present in the bag. Carrying out that multiplication we get 12.45% actual K or 6.22 pounds of actual K in our 50 pound bag.

Picture 3.JPGUnless there is a specific need to know the amount of actual phosphorus or potassium present in the bag we usually use the percent phosphate and potash for making fertilizer recommendations. Most soil test recommendations also base fertilizer needs on these same phosphate and potash percentages. Hence, when applying the amount of phosphate or potash suggested in the soil test recommendations, one will be applying the needed amount of phosphorus and potassium to the lawn. Picture 3.

Coming up

In next month's article, we will be taking a close look at the nutrient nitrogen as it is the nutrient required in the largest amount next to C, H and O. It is also the nutrient for which nearly all rates of lawn fertilizer applications are based. And, it may just be the reason why you would select one fertilizer over another. Check in next month for a thorough overview of this very important fertilizer nutrient.

Rust Diseases of Lawn Grasses Very Common this Fall

Bob Mugaas, UMN Extension Educator

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Photo 1: Areas of rust infection on Kentucky bluegrass lawn. Bob Mugaas.

Rust diseases of our lawn grasses have been on the increase throughout much of this fall period but became especially evident during the drier conditions of October. Rust infestations usually show up as areas of yellow to orange-yellow grass blades, see Picture 1.

Upon closer examination of the grass blade, one will usually see orange colored, tiny tuft-like pustules breaking through the grass leaf surface, see Picture 2. It is these pustules that produce massive numbers of individual spores. These are the same spores that can become air-borne and cover our shoes or lawn mowers in an orange 'powder' as we walk through rust infected areas of the lawn. They can also re-infect other grass plants that in turn can produce more of the same spore producing rust pustules thus carrying on the infection cycle.

What is a rust disease?

Rust diseases have very complex life cycles that include as many as five different stages during a single year. In addition, it is often necessary for various species of rust to spend a portion of their life cycle on one plant species and the other portion on an entirely different plant, often referred to as an alternate host. Such is the case with the specific rust disease known as crown rust (Puccinia coronata) of grass. This disease completes part of its lifecycle on its alternate host, common buckthorn (Rhamnus cathartica) or glossy buckthorn (Frangula alnus, formerly Rhamnus frangula), and the second portion of its lifecycle on some of our lawn grasses, especially perennial ryegrass and tall fescue. Other rust species including Puccinia graminis (Stem Rust) and Puccinia striiformis (Stripe Rust) can also affect Kentucky bluegrass, along with many other grass species.

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Photo 2: Spore producing rust pustles pushing through grass leaf surface. Bob Mugaas.

Rust on turfgrass can overwinter in plant debris but it will need to infect its alternate host before returning to the grass plant. It should also be noted that the disease causing spores can develop in warmer climates to our south and be blown up here during the summer and serve as a source of infection from summer into the middle of fall. This can be an important source of rust infection in this area. In a typical year and under favorable conditions, crown rust will usually start to show up toward the end of June while stem rust can be a bit later. Once begun, the rust infection cycle can continue throughout much of the growing season so long as favorable rust infection conditions persist.

Why rust and why now?

Slow growing lawn grasses are a prime target for rust disease attack. It is usually the combination of warm daytime temperatures, dry weather and heavy amounts of overnight dew production on the grass foliage that creates a favorable environment for rust spores to germinate and infect the foliage. When these common weather conditions are combined with low levels of available nitrogen, an element responsible for active, vigorous growth of our grasses, you have very favorable conditions for a rust outbreak. Shadier areas often experience greater incidence of rust. Note the lighter yellow to orange areas scattered around the lawn underneath the spruce trees in Picture 3.

Rust disease started showing up more frequently around the Twin Cities during late August to early September. However, it wasn't until the very dry conditions lasting nearly the entire month of October that significantly increased the occurrence of rust in our lawns and other turfgrass areas. Frequent enough rainfall combined with an occasional supplemental watering kept our lawn grasses actively growing and utilizing available nitrogen throughout much of the summer period.

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Photo 3: Rust infection on a partially shaded lawn area. Bob Mugaas.

Nitrogen can also be lost when it is carried with water down through the soil and beyond the reach of grass roots, a process known as leaching. Thus, due to relatively continuous grass growth during the summer and nitrogen losses due to leaching, it is quite likely that the amount of available soil nitrogen was in short supply by late summer, a time of year when our lawn grasses naturally resume active shoot and root growth. That condition along with the prevailing weather conditions during late September and much of October has contributed to a much higher than usual amount of rust disease on our lawns and other turfgrass areas.

So, what should I do now?

With the rains of the last few days of October, we have improved our previously dry soil conditions. That will be a big help in improving the growing conditions for lawn grasses. While it's late to be putting down nitrogen for this year, it would be a good idea to plan on applying some next spring as our lawns are beginning to show active growth. For the most part, we try to manage rust diseases by changes in our cultural practices. There are fungicides that can be applied in severe cases. However, at this late date in the season, both the rust fungi and the turfgrasses are preparing for winter survival and dormancy. Thus, fungicide applications at this time of year will be of no benefit. Use of protective fungicides can be reevaluated next year should serious rust problems begin to develop.

Where disease levels were quite high and there was some thinning of the lawn, one should be prepared to do some reseeding of those areas as needed. Some overseeding could be done yet this fall in a process known as dormant seeding. Normally this would be done once the ground is cold enough to prohibit germination with the seed remaining in the ground until next spring when it will sprout and grow. One could also wait until early next spring to do some seeding.

For some additional information on rust diseases of lawns, check out the following link to our Gardening Information page, What's Wrong with My Plant?

The author would like to gratefully acknowledge the input and review of Dr. Eric Watkins, Assistant Professor-Turfgrass Science, University of Minnesota Department of Horticultural Science and Michelle Grabowski, Extension Educator - Horticulture & Plant Pathology, University of Minnesota Extension, in the preparation of this article.

Pollinator Blues - Part I

Karl Foord, UMN Extension Educator

The Native Wild Pollinator's Perspective


Photo 1: Bumblebee on Cosmos. Karl Foord.

Most everything we do cuts into their territory. We make roads, houses, cities, and factories. We plant grass athletic fields, home owner lawns, double flower sterile plants, and we plant large agricultural fields of corn and beans all of which are in essence deserts for them. We use insecticides targeted for other critters and sometimes damage them in the process. We even mulch our gardens making it difficult for them to find ground based nesting sites. I can hear them singing the Jim Croce song 'Car Wash Blues' and changing some of the lyrics. "I got them steadily depressing low down mind messing 'I can't find no pollen' blues".

Short History of Insect Pollinators

Most animals and birds depend on flowering plants for food or shelter. Most plants depend on pollinators to complete their reproduction cycles. This makes pollinators key players in the ecosystem. It should be emphasized that the flowering plant pollinator relationship is kf2.jpg

Photo 2:Bumblebee on Golden Rod. Karl Foord.

one of long standing. Insects were around long before flowering plants. The oldest insect fossils date back to the Carboniferous (360 - 300 million years ago) and exhibit wings and other advanced features which suggests millions of years of evolution before the Carboniferous. There is still discussion about the timing of the origin of flowering plants. The ancestors of flowering plants diverged from gymnosperms in the early Triassic (245-202 million years ago), and fossils of flowering plants are dated to the early Cretaceous (145 - 65 million years ago). Flowering plants diversified during this time and became the dominant plant form in the late Cretaceous (100 - 65 million years ago). Suffice it to say that flowering plants and insects have been interacting intimately for at least 100 million years and have become quite codependent. So pollination is central to the life cycle of flowering plants and more than 80% of plant species rely on animal pollinators and 99% of those pollinators are insects.

Photo 3: Bumblebee on Golden Rod. Karl Foord.

The Pollinator-phile's Perspective

Pollinators are needed for the successful production of as much as 25% of everything we eat and drink, and we are rapidly depleting their habitats. Granted much of this pollination is done by the non-native honeybee. But as we shall see in next month's article by Marla Spivak these pollinators are facing their own set of problems. We need these native pollinators if for no other reason than help pollinate some of our important crop species as the honeybees face challenges. We are finding that bumble bees are much better pollinators of tomatoes in greenhouse and high tunnel settings than honeybees. This is true for many crops if you remember the pumpkin and its specifically adapted pollinators mentioned in the last issue.

All things considered I would like to join the ranks of the native pollinator friendly assembly,kf4.jpg

Photo 4: Bumblebee on Golden Rod.Karl Foord.

but what is one to do? Before becoming an advocate I would like to explore what I could do on my own without having to persuade some government entity that they should create pollinator plant refuges on the highway right of ways. This requires some consideration. The native pollinators are adapted to native plants but will glean pollen and nectar from cultivated species. All of our cultivated plants were adapted from wild ancestors. This leads me to consider two steps. First, take an inventory of the plants I those closely adjoined to my property, and access how pollinator friendly my homestead might be. Second, consider the array of pollinator friendly species and see what might fit within the existing landscape. I will address each in turn.

As far as the home inventory is concerned, I love dwarf evergreens so nothing there for the pollinators. But I have apples strawberries willows as well as significant patches of sedum and thyme. There is a buffer area on my property that is undeveloped and features phlox in kf5.jpg

Photo 5: Bumblebee. Karl Foord.

the spring and goldenrod in the fall. An adjoining school grassy area is mowed but does not control any weeds so the dandelions do quite well. I have some other plants but I will need to consider when they flower and how many there are to determine their impact.

As to plants attractive to native pollinators, I looked at lists of the plants and found I had my work cut out for me. When do they flower and for how long? What are their growing requirements and will they be bullies or gentlepersons in their interaction with the other plants in the landscape. So my next assignment is to work on this and see if the plant lists can be assembled in a way that the information can be applied to anyone's landscape; this for next time. In the meanwhile please enjoy some pictures of bumble bees showing their long tongues, choice of pretty flowers, and flying capabilities.

Bob Mugaas, UMN Extension Educator - Horticulture U of MN Extension and Brian Horgan, PhD. Associate Professor, Extension Turfgrass Specialist U of MN Department of Horticultural Science

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Photo 1: Receding flood waters from a public park. Bob Mugaas.

Flooding is not uncommon during spring and summer here in MN. Yet residents of southern MN are experiencing significant flooding this fall. Justifiably, repairing lawns and landscapes is probably not the highest priority. However, should attention turn to wanting to do 'something', here are a few tips regarding the assessment of potential lawn damage and options for repairing them, even yet this fall.

Have flood waters actually done any damage to my lawn? In general, where flood waters have risen quickly to cover the lawn area but also receded quickly (within 2 or 3 days), there has probably been little permanent injury to the lawn. With shorter days and cooler temperatures in fall, lawn grasses are usually able to remain green and alive through brief periods of being submerged. Picture 1. As flood waters recede and the soils dry, soil oxygen levels improve aiding plant growth. In this situation, little to no repair is usually needed.

In many instances, water flowing over river and creek banks gets trapped on your property and is not able to flow back to the river. Picture 2. In this situation, stagnant, flooded turfgrass conditions may persist for several days or longer. Water loss is now a function of evaporation and soil infiltration capacity rather than flowing back into the stream or river. Damage assessment can be done once the water has disappeared from the lawn.

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Photo 2: Ponded areas of water left behind receding flood waters. Bob Mugaas.

Where grass plants appear brown and rotten, it is safe to assume that the grass plants have died and this area will now need to be reseeded or sodded. On the other hand, if the water evaporated or infiltrated the soil within 2-3 days, grass plants may have survived. These temporarily flooded areas may not be as dense as they were prior to being inundated with water and some reseeding can be beneficial to restoring a healthy dense cover of turfgrass (see notes on overseeding later in this article).

In most cases, water continually moving across a lawn surface is less problematic for the grass plants than non-moving, stagnant water. The differences in these two water movement characteristics will often dictate the amount of sediment deposited on that lawn surface. Sediment deposited is often associated with slowing water flow or ponding.

The likelihood of permanent injury to lawn grasses will depend on the depth of that sediment deposit. If deposits are less than 1/2 inch, usually there are no serious problems for home lawn grasses maintained at higher mowing heights and the grass will still be visible above that sediment layer and continue to grow normally. Picture 3. However, even light sediment deposits can form a distinctly different layer of soil that can ultimately create future soil water and nutrient infiltration problems. To help prevent this occurrence, core aerification (two to three passes) over the lawn will break through the sediment layer thus avoiding future soil problems.

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Photo 3: Surviving turfgrass following short term submergence. Bob Mugaas.

Core aerification on home lawns can be done this fall once the areas have dried out sufficiently so that the area is no longer soft and muddy when walking across it. Additional core aerification can also be done in the spring just as the lawn is beginning to green up and again around Labor Day next year. This additional aerification in 2011 will help ensure healthier soil conditions that in turn support a healthier lawn.

Where resources may be more limited and aerification isn't possible, brisk raking will help break up that sediment deposit. Again, this can be done once the soil has dried and is no longer soft and muddy underfoot.

Where sediment has been deposited at levels deeper than about 1 inch and the grass is barely visible through the sediment, grass plants will likely die. In these cases, it is usually better to carefully remove some of that material and overseed to restore the lawn area. A thorough core aerification will be beneficial following sediment removal.

The late September to early October time period is a difficult time to successfully overseed and establish a new lawn. The lack of establishment and maturity achieved by the young grass plants often results in very poor winter survival thus necessitating another seeding in the spring. Therefore, we recommend waiting until the ground is cold but not frozen to sow seed (usually early to mid-November). This process results in seed that does not germinate this fall but begins to actively grow in the spring. This is known as dormant seeding and can give lawn seeds a head start on germination and growth next spring. While results of this practice can be variable, when done correctly and Mother Nature cooperates with sufficient snow cover, successful lawn establishment can be accomplished. The good news about considering dormant seeding is that attention can be given to dealing with home and property losses without feeling like something also needs to be done right now to fix a lawn.

A rather unintended consequence of fall flooding is the introduction of new weeds into lawns and landscapes. By late September, there are many annual and perennial weedy plants actively dispersing their seeds. Flood waters can be a significant means of spreading many of those seeds into places where those plants have never been present. While there is nothing to do right now, be watchful for new and different weeds showing up in lawns, gardens and landscape areas next spring and summer. Early removal or treatment with an herbicide is good practice and limits the amount of herbicide needed to achieve control.

While lawns are not a first priority when dealing with other home and property losses due to flooding, at some point down the road most folks will want to restore their lawns, gardens and landscapes thus restoring a sense of 'normal' to their lives. Hopefully, this information will be of help when that time comes.

Lawn Care Tips for October - Yes, Really, Lawn Care in October.

Bob Mugaas, UMN Extension Educator

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Photo 1: Healthy, vigorous late summer lawn.Bob Mugaas.

Even though much of the month of October can be one of the best times for grass growth and recovery, it's tempting to put away our thoughts, practices and equipment used to care for our lawns by the middle to end of September. The reason for this active period of growth is that the lawn grasses adapted to this area (e.g., Kentucky bluegrass, the fine fescues and perennial ryegrass) are best adapted to the cooler and usually moist conditions of spring and fall. See Picture 1. So, with that in mind, here are a few end-of-season lawn care practices that help support actively growing grass plants.

1. Mowing. So long as our grasses continue to grow, we should be continuing to mow as needed. With cooler temperatures and shorter days, mowing intervals usually become longer the later we go into the month. A common question at this time of year is "Should I cut my lawn shorter the last mowing of the year?" One reason to consider somewhat shorter mowing heights in the fall is the decreased (usually) incidence of snow mold come the following spring. Longer matted grass potentially creates more favorable habitat for the snowmold fungus to live and grow over winter. We see the results of that fungal growth the next spring when, as the snow melts and retreats from the lawn surface, the lawn appears covered with grayish or pinkish colored patches indicating the presence of snowmold.

However, reducing the height of a lawn should not be something reserved for only the last mowing. For example, if the lawn has been kept at about 2.5 - 3.0 inches during the growing season and the desire is to reduce that to two inches, then begin the process of gradually lowering that mowing height two to three mowings prior to your very last cutting. That will help the grass adjust to a lower height of cut more gradually instead of being scalped just before going into colder conditions; a more stressful condition for turfgrass. If the grass is still actively growing during October, you may need to mow somewhat more frequently in order to reach and then maintain the lower mowing height. This is because shorter heights of cut require more frequent mowing to establish and maintain them.

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Photo 2: Comparison of mowed (lower left) and unmowed (lower right) leaf covered lawn area. Bob Mugaas.

2. October is the month when leaves drop from our deciduous (leaf losing) trees. The spectacular fall colors of early October give way to leafless trees ready to face the winter months ahead. So, what to do with all of those leaves? A small amount (usually less than a couple of inches) of fall leaves can be left on the lawn surface and ground up with a rotary mower. Be sure to go over them several times such that the remaining leaf particles can more easily sift down into the lawn and soil surfaces. The lawn should look like it was raked when you are done. See Picture 2. If there are still piles of shredded leaves be sure to rake them off of the lawn surface and either compost them or use them as a mulch in other parts of the landscape. Leaves can also be removed from the lawn by picking them up using the mower's bagging attachment (if it has one) and redistributed as a mulch cover in another non-lawn part of the landscape or composted.

3. Early October is an excellent time to apply herbicides to perennial broadleaf weeds such as dandelions, creeping Charlie, clover, and plantain. See Picture 3. Where only a few weeds are present, hand removal can be just as effective as an herbicide. On the other hand, weed control products are now widely available in ready-to-use application containers. Hence, we can spot treat the specific weeds while introducing minimal amounts of herbicide to the environment. Where weeds are more numerous and scattered throughout the lawn, a broadcast application of an herbicide product can also be done. These can be applied either as a granular or liquid product. The products used should be weed control products only and not combined with a lawn fertilizer as this would not be a good time to be applying fertilizer. Always follow product label directions exactly - it's the law. Be sure the weeds (and lawn grasses) are actively growing at the time of application as the product's effectiveness will be much better than if weeds are growing under water stress. If necessary, water the area to be treated a day or two the planned application to help ensure their active growth.

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Photo 3: Common dandelion, a perennial weed effectively controlled with broadleaf herbicides in the fall. Bob Mugaas.

4. It hardly seems necessary or even appropriate to be talking about watering a lawn given the amount of rainfall and flooding issues experienced over the last few weeks. Nonetheless, should October turn dry and remain warm, lawn grasses will likely benefit from an additional watering or two before shutting down for the winter. In general, it's a good practice to not have lawn grasses go into winter conditions severely stressed due to lack of water. We don't need to follow the one inch per week at this time of year due to the cooler temperatures and shorter days. Both of those conditions slow the loss of water from the lawn and hence any watering required can be done at longer intervals. In other words, that same one inch of water per week, (including rainfall), during the summer months might be sufficient for two or even three weeks this time of year depending on weather conditions.

5. Finally, new suggestions for applying nitrogen fertilizers to Minnesota lawns no longer include a late October to early November application. In short, new research here at Minnesota and Wisconsin questions the usefulness of that nitrogen application due to the inefficiency with which it's taken up by the grass plant. Hence, the preferred late season fertilizer application time for Minnesota lawns is around Labor Day to the middle of September. Nitrogen absorption is much better at that time of year and it ensures adequate nitrogen nutrition for the grass plant going into a very active period of growth. For more information on this topic see the article in the August 1, Yard and Garden Newsletter.

Continuing through the fall with few important lawn care practices can help ensure a healthy lawn going into the winter months and a healthier lawn to begin the growing season next spring. Good Luck!

September Home Lawn Care To-do List

Bob Mugaas, UMN Extension Educator

Thumbnail image for bob2.JPG1. One of the very best times of the year to be fertilizing your lawn is from about Labor Day through the middle of September. Applications that put down about one pound of nitrogen per 1000 square feet will help provide the necessary nutrition through the late summer / fall period - a time of active grass shoot and root growth.

2. It is important to avoid serious water stress on lawns this time of year. As noted above, the late summer /early fall period is a time of active growth. Hence, not only is sufficient nutrition important but ample soil water is just as important to sustain and encourage growth. Early in September, the average rule of thumb of one inch of water per week including rainfall should be sufficient. As we get later into September and early October, that same one inch of water may be sufficient for two or even three weeks depending on weather conditions. That is, the warmer and drier the weather the more frequently plants will need watering. The cooler, and more moist the weather, the less frequently plants will need to be watered. Remember, soils should be just damp to the touch not soaking wet to provide a healthy place for roots to grow and beneficial soil microbes to flourish.

3. Early September is an excellent time to be doing some overseeding of damaged or thin areas of the lawn. Seed germination is usually much quicker due to the warmer soil temperatures. Hence, seedlings are able to get out of the ground and more quickly establish the area prior to the onset of colder conditions of late fall and early winter. If you're struggling with trying to get some grass growing under the shade of some maturing shade trees, try growing some of the fine fescues. They are well adapted to dry shade conditions and are tolerate much lower inputs of fertilizer and water while still remaining healthy. If seeding areas shaded by trees, be sure to keep lightly removing tree leaves as they fall. That will help ensure that seedlings receive sufficient sunlight throughout the fall resulting in better establishment. Keep newly seeded areas damp during the germination process and gradually back-off the water as they begin to get established - usually about three to four weeks.

4. One of the best times to be aerating the lawn is right around Labor Day. This minimizes the amount of germination from unwanted weed seeds making for less competition to the new grass seedlings. It also provides increased soil oxygen levels that encourage better root growth and a healthier soil microbial community. Lawn aerifiers that pull a core of soil and deposit that core on the lawn surface are the most effective units that are still relatively easy to use for homeowners. These soil cores can be left to decompose naturally over the next few weeks. There is usually not a need to remove these from a home lawn. If you are also planning some fertilizing, and/or want to do some overseeding, an excellent time to do that is right after you have aerified. Aerification can also be used to control the rate of thatch build-up as the decomposing soil cores help to reinoculate the underlying thatch with soil. In turn, that helps break down the thatch and keep the amount of thatch build-up to below damaging levels (i.e., less than ½ inch) Thumbnail image for bob3.JPG

When you think of fall as an active period of growth for your lawn grasses, the extra effort to ensure good growing conditions during that time helps ensure a healthy lawn going into the winter and a lawn quicker to recover and resume growth in the spring. Besides, late summer and early fall are some of the nicest conditions of the year to be tinkering with your lawn. Enjoy!

Summer Lawn Care on the Heels of a Wet and Stormy June

Bob Mugaas, UMN Extension Educator

With the recent rains and storms across the state, most lawns have had sufficient moisture to remain actively growing and green through the month of June. In fact, in some instances there has been too much rain causing lawns to remain in excessively wet conditions for several days or more at a time.


Photo 1: Temporarily ponded water from excessive rainfall.Bob Mugaas.

Under moderate temperatures and partly sunny or cloudy conditions, water that temporarily (a day or two) remains at or near the lawn surface is usually not a problem. (See Picture 1). Once the water drains away and soil oxygen levels rise such that normal root functions can continue, the grass will resume normal activity and growth with little to no evidence of having been temporarily submerged. However, under sunny conditions and high temperatures, lawn areas remaining in saturated soil conditions or submerged for even a few hours can suffer serious damage and even death. Once the moisture does recede, grass plants will appear dark brown to black indicating they are no longer alive. These areas often have a foul smell associated with the dead and dying plant tissue. Following those conditions and once the area has dried out, it will be necessary to reseed or resod the area due to the grass that has been killed.

Moist conditions in the lawn have also given rise to the random appearance of many different kinds of mushrooms. These are the result of fungi feeding on the dead and decaying organic matter in the soil and thatch layers of the lawn. As these fungi continue to grow and carry out their decomposer role in the soil and thatch, they will periodically, especially under moist conditions, send up fruiting structures that we know and see as mushrooms. See Pictures 2 & 3.


Photo 2: Lawn mushrooms emerging during moist conditions.Bob Mugaas.


Photo 3: Another species of mushroom growing in the lawn. Bob Mugaas.

These are not indicative of problems in the lawn or of an impending lawn disease outbreak. Most of these fungi carry out the beneficial process of decomposing soil organic matter which ultimately helps recycle nutrients back to the grass plants for growth and development. There are fungi that cause the appearance of darker green circles or arcs in the lawn. This pattern or symptom is commonly known as fairy ring. See Picture 4. If these are what you are seeing, you can check out turfgrass disease section of Extension's Gardening Information page: for more information. One should not eat mushrooms appearing in the lawn! Where there is concern about children or pets possibly consuming them, simply break them off with a rake, pick them up and dispose of them in a manner that keeps them completely out of the reach of children or pets.


Photo 4:"Fairy ring" in lawn. Bob Mugaas.

With the excessive amount of rainfall and the continued vigorous growth of our grasses all during June, it is very possible that our lawns will benefit from a light application of nitrogen fertilizer. Nitrogen can be lost in a number of ways from the lawn including leaching (i.e., carried with water draining through the soil), gaseous loss back to the atmosphere and taken up and used by grass plants for growth. Hence, under the moist conditions and rapid grass growth that we have been experiencing lately, many of our lawns will benefit from ¼ to ½ pound of actual nitrogen, per thousand square feet. It's important to not fertilize excessively going into and during the potentially hot summer months of July and August. That can unnecessarily stress the grass plants and perhaps result in injury during those hot, dry summer periods we expect to encounter in Minnesota during July and August.


Photo 5: Excessive clippings from waiting too long to mow. Clippings should be removed from lawn surface before causing damage to underlying grass. Bob Mugaas.

While it's tempting to mow the grass much shorter once it has gotten too long, that will be extremely stressful for the grass plant and actually results in a slowing or even stoppage of growth and recovery, and perhaps even the death of some plants. That slowing or stopping of growth may seem like just the result you are looking for, but, it's really not. Our lawn grasses are much healthier, competitive, and stress tolerant when they grow at relatively uniform rates. Under those conditions, the amount of food produced by the leaves is sufficient to meet the plants growth needs as well as create some additional stored reserve. When large amounts of leaf and stem tissue are removed at a single mowing, shoot and root growth slows or even stops. That additional stress can open the door to certain disease and insect problems as well as increased potential for weed invasion while the grasses are recovering. If the excessive clippings are left on the lawn, there can be enough sunlight reduction to the plants underneath the clippings that they can be injured or even killed causing a thinning out of the lawn. (See picture 5.)

The loss of large amounts of leaf tissue all at one time forces the use of stored plant reserves just to survive. As a general rule, when our grass growth gets a little too far ahead of us, initially mow as high as your mower will safely allow. Then, begin lowering the height of cut by mowing more frequently and gradually reduce the mowing height back to the desired level. This is much healthier and less stressful for our lawn grasses.

Bob Mugaas, UMN Extension Educator - Horticulture

Minnesota lawn grasses are known as cool season grasses as their peak periods of growth and activity occur during the (usually) cooler seasons of spring and fall. These grasses include Kentucky bluegrass, fine fescue, perennial ryegrass and tall fescue. The middle of May through most of June is the prime flowering period for these cool season grasses in Minnesota. Kentucky bluegrasses tend to be the first of the grasses to begin flowering with the fine fescues, perennial ryegrasses and tall fescue coming on slightly later. See Picture 1 of Kentucky bluegrass flowering.


Picture 1. Kentucky bluegrass flowering

Photo 1: Kentucky bluegrass flowering. Photo: Bob Mugaas.

Grass flowering is an entirely normal process whether observed in a mowed lawn or an unmowed area. However, the height of the flowering stem will usually be slightly to significantly taller in an unmowed situation than a mowed lawn. The initiation of the flowering process actually begins late the previous fall when the growing point (crown) of a mature grass shoot goes through a biological change from producing stems, roots and foliage during the late summer and early fall period to one that will produce a flowering stem the next spring. The crown remains in that condition until the following spring. As temperatures warm and day length gets longer during late April and May, these shoots begin to send up a flowering stem known as a 'culm' in grass terminology.

In most instances, even if we are regularly mowing the lawn, these shoots continue to elongate in an attempt to produce their flower cluster known as an 'inflorescence'. See picture 2. The result of mowing regularly is that we often do not see the fully elongated flowering stem


Picture 2.  Kentucky bluegrass inflorescence

Photo 2: Kentucky bluegrass inflorescence Photo: Bob Mugaas.

and hence, the lawn appears normal and we observe little to no grass flowering. Whether mowed or unmowed, or whether a flower cluster was visible or not, these flowering shoots eventually die off during late June and into early July. This is often a time when folks express concern about their lawn looking a little thin and lots of brown stemmy material in the lawn. As it is entirely normal for these flowering shoots to die once flowering is completed, lawns can temporarily look a little thinner. The apparent increase in brown stemmy material is actually the remnants of those original flowering stems. Eventually, they will fall back into the turfgrass canopy and begin decomposing leaving little to no evidence of their prior function.

Of course, not all of the shoots present in a lawn will have gone through the biological changeover to a flowering 'bud' the previous fall. Hence, our lawns have enough growing shoots present, even though the lawn may be a little thinner, it still looks and functions like a lawn. Also, by the time we get to early August, a new round of grass shoots will be starting to form along with the production of new leaves, rhizomes, tillers and roots. This growth will continue through the fall period when once again grass shoots with sufficient biological maturity will make the changeover to flower buds that will again produce next spring's flowering shoots.

Because these flowering stems temporarily disrupt the otherwise uniform appearance of a healthy lawn surface, their presence is often viewed unfavorably. The important point here is that grass flowering is a normal, temporary condition common to most lawns. There really is little that we can control within this naturally occurring process. If desired, mowing slightly shorter for a couple of times to remove more of the inflorescence can make the flowering stems less apparent. Also, increasing mowing frequency for 2 to 4 weeks during peak flowering will help keep flowering stems from becoming too visible and disruptive. However, since flowering occurs just before the warmer and drier parts of the growing season, it will be important to raise mowing heights back up as soon as possible to encourage as much root growth and rooting depth as possible before those more stressful conditions settle in.

On the flip side of the grass flowering question is whether or not any of seed produced will actually provide some 'reseeding' back into the lawn. In other words, if one lets their lawn go to seed will they receive some benefit from the seed produced in terms thickening up the lawn. The short answer to that question is usually not. Since the process of mowing continually cuts off the developing flower cluster, any seed that starts to develop doesn't reach sufficient maturity to actually be viable. In an unmowed situation such as would be the case in a seed production field, the flower stems are allowed to fully ripen, turn brown and dry. The seed is then harvested just before it has a chance to naturally disperse from that dried flower cluster. That harvesting usually occurs from mid to late in June to perhaps early July.


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Photo 3: Healthy Kentucky bluegrass Photo: Bob Mugaas.

While flowering grass stems may be an unsightly disruption to an 'attractive', uniform lawn surface, remember this is an entirely natural process of our grass plants. It is also important to keep in mind that this is a temporary process that runs its course over a few weeks in mid to late spring. Once that cycle is completed, those remaining shoots that did not flower as well as newly produced shoots continue to grow and fill-in those thinner, empty spots left behind by the dead flowering shoots. See Picture 3.


Bob Mugaas, University of Minnesota Extension Educator

Snowmold recovery

This spring began with the very early snowmelt in mid-March that left in its wake one of the highest incidences of snow mold on many residential and commercial lawns in recent memory. Much of that could be attributed to the very wet snow that fell around Christmas time on unfrozen or barely frozen lawn surfaces. The high moisture content of the snow combined with the mostly unfrozen lawn conditions provided nearly ideal conditions for the snow mold fungi to grow and thrive. In addition, that snow cover was maintained throughout the winter months providing a very long period of total snow cover and good conditions for snow mold growth. However, as is often the case, even with as much snowmold as was evident this spring, most lawns will have recovered on their own and returned to healthy growth and good green color by early May. The severity of snowmold on some lawns did result in the need for some reseeding to fill in thin areas resulting from that injury. Photos 1 and 2 show a commercial site affected with snowmold earlier this spring that has now grown out of those symptoms without the need for reseeding or other repair. A light application of fertilizer and some watering as needed this spring will help further restore and invigorate those areas. 

Photos 1 and 2: Snowmold infestation and turf recovery. Bob Mugaas

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Meadow vole damage and recovery

That continuous snow cover over winter also created a good habitat for meadow voles to invade our lawns resulting in slight to extensive surface tunneling in lawns, especially those close to unmaintained grassy areas such as next to vacant lots, prairie edges or other nearby grassy areas where voles retreat to after the snow melts. See Photo 3 for typical injury associated with meadow voles in lawns. For the most part, these critters tunnel along the surface eating a variety of vegetative material including the grass. One may observe tunnels traveling over and through the lawn surface. It is often common to see loose grass 'clippings' mounded up over the tunnels creating a slightly raised appearance to the seemingly random tunnel patterns. While the grass foliage is eaten by the voles, the grass plant crowns (growing points) often escape being eaten and are responsible for the regeneration of new leaves and stems that ultimately fill in the tunneled areas. Since the plant is having to start from scratch in its spring regrowth, the tunneled areas frequently lag behind the rest of the lawn area in spring recovery but do ultimately catch up to the rest of lawn in terms of height and density. See Photo 4 of new grass shoots coming in a surface tunnel caused by voles. Again, a light application of fertilizer and water as needed will help restore the growth and vigor of these areas. In nearly all cases, recovery occurs without the need for reseeding or replacing the damaged areas.

Photos 3 and 4: Vole damage and indications of turf recovery. Bob Mugaas.


Early season mowing

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Photo 5: Turfgrass color variances associated with differing heights of growth prior to first mowing. Bob Mugaas.

By the writing of this article most of us have had to mow our lawns at least once or even twice already this season. In some cases, there appears to be areas of yellow or lighter green grass following mowing, especially the very first mowing of the year. See Photo 5. With the typical unevenness of that very early spring growth prior to the first mowing, it's not uncommon to see lighter areas intermingled with normal darker green areas. The lighter areas are usually associated with grass that had grown vigorously early and was taller than much of the surrounding grass. Hence, when its mowed at regular mowing heights, the grass ends up being cut back into lower blade and sheath tissue which is often lighter green to almost yellow due to the lack of chlorophyll. Cutting into that area of the plant is very stressful for the grass plant as it eliminates much of the leaf surface responsible for making the plant's food and can slow or even stop root growth temporarily until the plant can regrow sufficient tissue to resume normal growth. Grass that has not grown so vigorously or just grown more slowly ends up not being cut back so severely and hence retains its normal medium to dark green color and relatively uninterrupted growth. In most instances these early growth differences even out by the third or fourth mowing. Mowing higher rather than shorter, especially for the first cutting or two may help avoid cutting those taller areas too short initially while still being fine for the rest of the lawn area. This will also avoid the generation of excessively long and large amounts of clippings as also seen in Photo 5. When this quantity of clippings is generated from mowing, they should be removed or at least more uniformly dispersed over the lawn surface so as not to remain in large clumps, which can interfere with the healthy growth of grass plants underneath the clumps.

Crabgrass arrives early too!

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Photo 6: Crabgrass seedlings visible April 20, 2010 near a curbline in North St. Paul, MN. Bob Mugaas.

By the middle of April, crabgrass seedlings were already emerging in what are termed heat sink areas. These are areas that warm more quickly during the early part of the growing season and hence growth in these areas is usually well ahead of the majority of the main lawn areas. Examples include areas next to sidewalks, driveways, curbs, narrow boulevards, unprotected bare soil areas and the like. Usually the warming effect extends less than two feet from these paved areas back into the main lawn. Other exposed soil areas, especially those with south and west exposures generally warm more quickly than those covered with some form or vegetation or mulch. In addition, sandy soils tend to warm more quickly than heavier clay soils. Since drier soils are warmer soils compared to moist soils, the lack of early spring precipitation over much of the area caused soils to dry more quickly with the above average temperatures and sunlight. This also contributed to warmer than usual soils that in turn saw some of the earliest crabgrass germination in quite some time in the Twin Cities area. See Photo 6 of newly emerged crabgrass seedlings near a curb area.

Once crabgrass has emerged from the ground and is visible, it is too late to apply preemergence herbicides for crabgrass control. These products act on the newly germinating crabgrass seedlings prior to their emergence from the ground. In this case, one will need to use products containing the active ingredients quinclorac or fenoxaprop-p-ethyl. Both of these are available through commercial lawn care firms. Quinclorac can also be found in some homeowner lawn weed control formulations. Check the product label for its list of active ingredients. For very small infestations, it may be practical to manually remove them. In either case, treating the seedlings while they are still small and tender is much more effective than when plants are larger and more mature.

Just because you may have already observed some crabgrass germination in those heat sink areas, it doesn't necessarily mean you shouldn't apply a preemergent crabgrass control product to the rest of the lawn area if it's needed. However, it should be applied very soon, like within the first week or so of May, depending on your specific site conditions. Soil temperatures in the main lawn areas will lag behind those in heat sink areas, but they do catch up fairly quickly as temperatures continue to warm, especially overnight temperatures. Even though crabgrass germinates earlier in those warmer soils, it doesn't germinate all at once. Hence, an application of preemergence herbicide in those heat sink areas can help prevent later germinating seeds from getting started but won't kill those already sprouted.

Easy-does-it for spring fertilizing

Usually about the time the lawn is greening up and in need of its first mowing is a good time to consider applying a spring application of lawn fertilizer. For many of us, that time may have already passed. However, that doesn't mean it's too late to fertilize the lawn. In fact, sometime within the first three to four mowings of the year is still a good time to fertilize. Regardless of the situation, it's wise to not be aggressively fertilizing your lawn in the spring, especially with large amounts of nitrogen. That's best left for the late summer period.

In the spring, there is a natural, normal flush of growth by our grass plants. It begins with active root growth followed by rapid shoot growth. As shoot growth begins to accelerate, root growth tends to slow down. If too much nitrogen fertilizer is applied, shoot growth will be even more rapid resulting in a more frequent need for mowing but is also unhealthier for the grass plant. Excessive growth stimulated by too much nitrogen creates a more succulent plant that in turn requires greater amounts of moisture to sustain its growth. That increased succulence is more vulnerable to injury from summertime stresses and can be more prone to certain disease and insect infestation. The bottom line is, use moderate to low amounts of N in the spring to maintain balanced, but healthy, turfgrass growth. For more information on lawn fertilizing, see the publication Fertilizing Lawns (

Water if needed to support early season growth

While we often don't think of watering our lawns much before sometime in May, this year, due to the drier than normal conditions and earlier than normal vigorous grass growth, watering may be needed to sustain healthy, early season turfgrass growth. Early spring is the time of year when grass plants are actively growing new and deeper roots. That allows the plant to mine water and nutrient reserves from a larger soil volume, which, in turn, sustains the continued healthy growth of new shoots and roots. At this time of year watering deeply but infrequently is a good practice. Thus, an inch of water per week (or longer interval depending on weather conditions) including any rainfall that occurs will help keep soils moist and promote healthy root growth. If you have heavier, more clay-like soils where it takes a long time for water to infiltrate into the soil, it's usually best to apply a couple of lighter applications allowing time in between for the water to soak into the soil. Likewise, on lighter sandy soils that drain more rapidly, infiltration is not so much a problem as is the likelihood of water moving too quickly down through the soil and beyond the grass plant's roots and therefore not benefiting the grass plant. Hence, a split application of water will also be more beneficial for the grass on sandy soils.

While spring has indeed arrived ahead of most years, the tasks of lawn care remain much the same except that they need to be carried out earlier than many of us are used to. Paying attention to prevailing weather conditions and observing what's happening in your lawn are very valuable aids when it comes to understanding what's going on and what to do next.

Lawn Grass Varieties, Seed Labels, and What to Plant Where

Bob Mugaas, University of Minnesota Extension Educator

This is the third and final article in a series of articles related to choosing and selecting the best MN adapted lawn grasses for this area. This last topic will address the topics of what to do when you can't locate the particular grass varieties you've identified, how to read a grass seed label to know what you're really buying and some suggestions for the kind of grass seed mixes to use in various locations around our home landscapes. The previous posts are listed here: 

Series: Choosing and selecting the best MN adapted lawn grasses

Tips for selecting the best available grass seed varieties


Photo 1: Kentucky bluegrass seed sold in bulk. Karen Jeannette.

Selecting and then finding specific varieties of grass seed is not always as easy as you might think. Unlike the relative ease of finding your favorite tomato or marigold varieties through seed catalogs or the internet, looking for specific grass varieties can be much more challenging. It can be quite frustrating to go to a local garden center expecting to find at least some of your particular grass varieties but not see one of them listed on any of the grass seed labels carried by that retail outlet. Instead there are varieties listed that are completely unfamiliar to you. So, what's a person to do?

First, it's important to remember that not all varieties from a seed grower/supplier available in the marketplace will have gone through one of the state and/or national evaluation programs mentioned in last month's article. Indeed, seed growers and some supply companies will have also conducted their own independent variety research. From that research, they will make determinations about what varieties would be suitable for use in mixes to be packaged and sold in the retail or wholesale market.

Second, availability of particular varieties can also be a function of supply and demand characteristics. In some cases, the demand for a particular variety or varieties for use in larger wholesale markets (as well as for sod production) can exceed the supply of those varieties leaving little or none left to be packaged into the homeowner available quantities. In other instances, the availability of seed from particular varieties may be quite low for that year due to a number of possible causes (e.g., poor seed production, adverse weather conditions, etc.) Once again, those particular varieties may not show up either in commercial wholesale mixes or in the seed mixes available at local garden centers or retail outlets.

Finding recommended grass varieties, or the next best thing

So, that still leaves us with the question of "What's a person to do when they can't find the particular varieties they've identified?" One thing that can be done is to jot down the names of the varieties that are listed and go back to the resources mentioned in last month's blog and see if you can find anything about those particular varieties. As with many other things that we purchase, cheaper prices can mean lesser quality. The same would also be true for purchasing grass seed. In general, high quality, 'clean' seed will generally cost more but will almost always provide better results. Staying with reputable, highly regarded name brands of grass seed is usually a good first step even though the specific varieties you were looking for don't seem to be contained in the packages. In other words, the suppliers will most likely still try to provide good quality cutivars that will in turn help the end user, you and me, to achieve good results with their seed mixes. It's also important to remember that seed cost is usually going to be the least expensive item relative to the work and preparation needed to ensure the conditions necessary for successful seeding. Buying cheap, poor quality seed, can jeopardize a project's success no matter how careful all of the preparation work might have been done.

Interpreting the grass seed label

The next logical question one might be asking is "How can I tell if I'm getting both good value and quality in a seed mixture?" That question can best be addressed by examining the different parts of a grass seed label for information that can shed some light on grass seed quality.

Determining what is high quality seed need not be that difficult. Purchasing high quality seed can be easier if you understand a few basic terms on the grass seed label. Figure 1 is a fictitious grass seed label that will be used to discuss the various components of a label. All labels must provide information about the grass seed purity, its germination potential, crop seeds present, weed seeds present, noxious weeds present, and inert components in the package.

Much of the grass seed available in Minnesota comes from the west coast states where climates are most favorable for seed production. However, the very northern reaches of Minnesota are also home to a number of large, well established grass seed production farms. Seed from that area is also available through various outlets in Minnesota. Below Figure 1 is a list of terms you will find on grass seed labels and what they mean.

Terms Found on Grass Seed Labels

  • Lot number. This identifies the larger seed lot from which this particular seed came from. If there are issues related to the purity or growth of this mix, the lot number can be very important in tracing back to where problems might have originated.

  • Test date (month/year) It is always important to buy 'fresh' seed, that is, seed that has been tested within the year when it is purchased. This information tells when the seed was tested and determined to have the characteristics described further on in the label. It is also a useful date when one is trying to determine how long a particular bag or box of grass seed might have been stored and whether it will still grow or not. In general, it is usually better to buy new, fresh seed if more than two or three years old. This will be especially true if the seed has been stored anywhere else other than in cool to cold, dry storage. In most cases storage in garages or basements will not provide the necessary storage conditions to retain good seed viability. Again, in the bigger scheme of things and relative to the seeding preparation investment, the purchase of fresh, good quality seed is likely to be the least expensive part of the project. Bottom line: Always purchase and use fresh seed!

  • Variety These will be the names (when possible) of the actual turfgrass varieties contained in the mixture. In some instances, you will notice a generic term for a species of grass but no specific variety listed. For example, you might see the term 'creeping red fescue, VNS'. The VNS indicates 'variety not stated'. In other words, you know that you are getting a percentage of creeping red fescue but not which specific variety it may be. One shouldn't necessarily consider the term VNS to mean that the grass contained in the mix is a bad grass variety. There could be a number of valid reasons for not being able to list a particular variety. In most cases though, good quality seed mixes will usually try to list specific varieties whenever possible. 

  • Purity (Pure seed) is the percent by weight of pure seed, crop, weed, and inert ingredients in the package. These percentages added together should total 100 percent. Purity is concerned only with quantity, not quality. That is, not all seeds present in the package are capable of growing. To determine the seed that will actually grow or what is known as pure live seed, the percentage purity should be multiplied by the germination percentage. In this example, 31 percent by weight is Kentucky bluegrass (purity). The germination percentage for that variety of Kentucky bluegrass is 80. If one multiplies the purity value times the germination value you will determine how much of the seed will likely grow (under favorable conditions). When carrying out this calculation you will come up with a value of 24.8%. In other words, of the 31% Kentucky bluegrass contained in the mix, 24.8% of it actually has the capacity to germinate and grow. It should be apparent that you should always seek to purchase the highest purity of grass seed compared to the other contents and the highest germination percentages as possible.

  • Germination is the percent of pure seed that will germinate and grow in an ideal laboratory environment during a prescribed length of time. Since field conditions rarely duplicate these laboratory conditions, it is especially important to purchase seed with the highest germination percentage possible. As noted above, this is the percentage used to determine pure live seed.

  • Crop is the percent by weight of seeds normally considered to be grown as an agricultural crop such as grain. This can include other types of grasses that may be undesirable in a lawn. This percentage should be as close to zero as possible.

  • Weeds refer to the percent by weight of all seeds in the package that are not otherwise listed in pure seed or crop. It is not required to identify these weeds or how many there are since this is on a percent by weight basis. For example, one or two large seeds of a weed would pose no particular threat to the new lawn. However, even a small percent by weight of very small seed could account for thousands of weed seeds distributed over the area. This percentage should always be as low as possible.

  • Noxious weeds are listed as the number per pound, not the percentage per pound. Noxious weeds are weedy plants considered by individual states to be very difficult to control and that could pose hazards to both humans and livestock. While this is often more of a problem in farm crop seed, one should always purchase grass seed without the contamination of any noxious weeds.

  • Inert is the percent of material contained in the package that will not grow under any condition. Broken and damaged seeds, chaff, and empty seed hulls are just some of the more common inert material included. Obviously, this percentage should be as low as possible.

First Things First: Right Grass Seed - Right Place - Right Function


Photo 2: Side-by-side comparison of Kentucky bluegrass and fine fescue grass species. Bob Mugaas.

The final information in this article is intended to provide some help in choosing a particular mix of grass seed for particular areas and uses in our yards.
  • Avoid the temptation of a one-seed-mix-fits-all approach to purchasing grass seed for your property.
  • Pay special attention to site differences that may require a different mixture of seed to perform well. The most obvious of these conditions is for one area to be shady while the other part of the yard is in full sun.
  • It may be necessary to choose multiple grass seed mixes for the same residential site in order to have the best adapted grasses planted in the different site conditions. Below is a guide to a number of possible grass seed mixes to fit various needs.
  • Choosing the right plant for the desired location is of utmost importance for long-term plant health. 
  • Match the intended use of the lawn area with the proper types of grasses when choosing turfgrass varieties, blends or mixes. See below for site examples to help you match appropriate turfgrasses with the intended site and function.

Site Examples: Matching lawn site and function to seed varieties

Full-to-partly sunny conditions with minimal traffic or wear, low-to-moderate inputs intended.
  • 60% to 70% Kentucky bluegrasses, 20% to 30% fine fescues, ~10% perennial ryegrass.
Site 2:
Full-to-partly sunny conditions with moderate-to-high levels of traffic and/or wear, moderate-to-high inputs required for rapid recovery:
  • 75% to 85% Kentucky bluegrass, ~15% to 20% perennial ryegrass.lawn for partshade.jpg

Photo 3: Area well suited to Kentucky bluegrass fine fescue combinations such as those for site examples #1 or #3.Karen Jeannette.

Site 3: Shaded for a portion of the day or receives partial shade all day with minimal traffic or wear, primarily a dry shade:
  • 65% to 75% fine fescue; 25% to 35% Kentucky bluegrass (shade tolerant cultivars); ~10% perennial ryegrass.
Site 4: Shaded for a portion of the day or receives partial shade all day with minimal traffic or wear; a somewhat moist shade:
  • <30% to 40% fine fescue; 25% to 35% Poa trivialis, 20% - 30% Kentucky bluegrass (shade tolerant cultivars) ~10% - 15% perennial ryegrass.
Site 5: Full sun-to-very light shade, little to no inputs intended

  • 70% to 85% fine fescues; 10 - 20 % common Kentucky bluegrass; 5 to 10% perennial ryegrass.
Notes about using Ryegrass (Lolium perenne) and Roughstalk bluegrass (Poa trivialis) species in grass seed mixes:
  • Be a little cautious when adding perennial ryegrass to a mix. Research has shown that a 50/50 mix of Kentucky bluegrass to perennial ryegrass results in a stand that may be dominated by perennial ryegrass even though there are many more seeds of bluegrass than perennial ryegrass in the mix.
  • Because of the seedling vigor of annual ryegrass, it is sometimes used in general-purpose seed mixes; but almost never in mixes for "elite" or "premium" turf.
  • Note that the bluegrass species, Poa trivialis, sometimes referred to as roughstalk bluegrass, is better adapted to shadier more moist conditions and usually becomes the dominant species over time in that environment. However, because of the potential aggressiveness of Poa trivialis under favorable growing conditions, some people prefer to avoid using it even though it is well adapted to those conditions.

Hopefully, this article along with the other two previously published articles, Know Your Minnesota Lawn Grasses ( and So what are the best grass varieties? (, you'll get a good start on selecting and purchasing the best adapted, highest quality grass seed for your particular situations.

Repairing Spring Flooded Lawns

Bob Mugaas, University of Minnesota Extension Educator

Early spring, before lawns are actively growing (i.e., foliage is still mostly brown) lawn grasses can withstand several days of being submerged without suffering serious damage. If floodwaters are cold (<60 degrees F.), as they usually are in early spring, lawn grasses can withstand being submerged for even longer periods of time.

Moving water is usually less harmful to lawn grasses than is ponded, stagnant water. Ponding occurs in areas of poor drainage or results from water being left behind in valleys and depressions when floodwaters recede. Spring flooded lawn areas where the water has risen and then receded rapidly often escape serious permanent injury and death.

Post flooding lawn care

Once the soil has dried sufficiently such that it is no longer soggy and slushy underfoot, pick-up and remove debris such as wood, glass, stones, sheet metal, paper products along with other forms of junk deposited by flood waters. It is even good to remove thick layers of leaves or other debris that can smother the grass. Debris can be a safety hazard so exercise caution when picking up and handling this material. Debris left behind can later become a hazard to people operating lawn equipment as well as damaging the equipment itself. It should be noted that the drying process may take two or three weeks, perhaps longer, depending on site conditions.

Assessment of potential lawn damage and recovery may not be possible until those areas have dried. Checking for new shoots emerging from the soil or the emergence of new shoots from surviving plants is a good way to make an early assessment of damage. Usually, once regrowth has begun, it will continue although it may take several weeks before the lawn has completely filled in and begun to thicken up.

Often a more significant effect of flooding is the deposit of sediment, primarily silt, over lawn surfaces. This can lead to serious soil layering problems and even death of existing grass.

Lawn repair solutions for floodwater soil deposits less than 1 inch

Core aerification can be one of the most important and beneficial operations conducted where silt deposits are less than an inch and water has not ponded long enough to cause substantial death of the lawn. When the lawn has begun to actively grow as evidenced by new green grass blades appearing, go over the lawn about 3 times with a core type aerifier. This will help improve overall soil structure, improve soil oxygen levels, help break up soil layering problems caused by the overlay of silt and encourage recovery during the remainder of the growing season. A second round of aerification in early September will be helpful in further promoting active turfgrass growth and recovery through the fall period.

Overseeding can also be done at the time of aerification. Be sure that good seed to soil contact is achieved. To prepare a smooth seed bed, break up the aerification cores with a lawn rake or power rake (i.e. vertical mower). If desired, lawn seeding can be delayed until mid-August through early-September. Sodding can be done successfully throughout the growing season.

Lawn repair solutions for floodwater soil deposits more than 1 inch

Soil deposits in excess of an inch and just barely covering the turfgrass plants should be carefully scraped or washed from the lawn surface prior to any reestablishment. This will also help remove any floodwater pollutants left behind that may have a more lasting detrimental effect on the lawn since their concentrations are completely unknown.

If the lawn area is completely buried with inches of silt, then the best renovation strategy may be to accept that the majority of the lawn has already been severely damaged or killed and it will be necessary to reestablish a "new" lawn. Even though the process of silt removal is a lot of work and can be very damaging to existing turfgrass plants, reestablishing a lawn should begin by removing the excess silt as completely as possible. This should be followed by good soil preparation practices whether the lawn is to be seeded or sodded. See Extension factsheet 5775 Seeding and Sodding Home Lawns ( for more information on seeding or sodding a new lawn.

Where soil removal is not possible, rototill or plow the area thoroughly mixing the soil deposits from the floodwater with the existing soil and dead turfgrass cover. This will help restore more uniform soil conditions creating a better environment for grass to reestablish. One of the main goals of this operation is to help break up soil layering problems that can be caused by the silt deposits as well as the old sod layer. Seeding or sodding can be done as described in the above mentioned publication.

Introduction of new lawn weeds

Another problem that may be encountered with silt deposits is the introduction of potentially new and different weeds to the lawn. Therefore, it may be necessary to use pre- and/or post-emergence herbicides where appropriate during the reestablishment process. Make sure to follow labeled recommendations when using any herbicide to avoid injury to the young grass plants.

Extension resources for lawn repair

While dealing with the lawn may be the very least of one's water problems this spring, those needing to repair their lawn can do so once the soil has sufficiently dried. Local County Extension offices should have the publication FO-3914 entitled Lawn Renovation for additional information on repairing lawns. (The online link is:

So, what are the best grass varieties for this area?

Bob Mugaas, University of Minnesota Extension Educator


Resources for turfgrass species selection

Determining and then finding the best lawn grasses for one's lawn is not as simple a task as it might seem. However, there are at least a couple readily available resources about turfgrass species and varieties that are helpful when trying to determine which ones will do well in this area. One of those is a local source from right here at the University of Minnesota. The other is a national database with extensive information about turfgrass varieties. Let's see how we might utilize these to make a list of suitable varieties for this area. UofMN NTEP trials(2) - med.jpg

Photo 1: U of MN NTEP perennial ryegrass trial Bob Mugaas.

We'll begin with a look at the national database known as NTEP, the National Turfgrass Evaluation Program. Their information can be accessed at: This program is a cooperative effort between the non-profit National Turfgrass Federation, Inc. and the United States Department of Agriculture. It conducts comprehensive evaluations of turfgrass species and varieties across the country in cooperation with researchers at state Universities. (See Photo 1. U of MN NTEP perennial ryegrass trial). The evaluation data is submitted to NTEP for review, analysis and publishing. As a result of that effort, reports are created and made available to anyone wishing to view that data at no cost. For more information about the organization and what resources they can provide, visit their website mentioned above. They also provide a variety of helps to help navigate through the information.

Determining well adapted varieties

Variety information provided by NTEP as well as many others use a very common statistic known as 'least significant difference' or LSD to help aid the user in determining which varieties show true differences from the others being evaluated. This statistic also comes with a probability value that indicates these differences would occur either less than 5% or even less than 1% of the time strictly by chance. Hence, that gives us some level of certainty that the observed differences were not just a chance occurrence but are real differences between the varieties. Fortunately, the LSD and its probability value will have already been determined by NTEP or by the organization doing the data analysis. It is usually found at the bottom of charts that list various variety ratings for a particular characteristic.

For example, when looking down a column of numerical rankings, there can easily be questions about which of these varieties are really superior to all or any other varieties. That would be a perfectly fair question and hence, the need for a tool to help separate the top performing varieties from the rest of the pack. This is where we use the LSD statistic.

Here's how it works. Let's suppose we have the following (fictitious) ranking of bluegrass varieties based on their overall turfgrass quality during the year. In other words, which of these varieties consistently exhibited the best overall turfgrass quality? In this case the rating scale is 1 to 9 with 1 being virtually dead and the lowest quality and 9 being the very best overall turfgrass quality. In most cases, a rating of 6.0 or above would be considered acceptable for a home lawn situation.


Variety Turfgrass Quality

Variety A 7.1

Variety G 7.0

Variety Y 6.8

Variety B 6.8

Variety M 6.7

Variety J 6.4

Variety S 5.7

Variety C 5.6

Variety R 4.4

Variety H 3.7

LSD 1.3

As noted above, these are all fictitious numbers but they will serve to illustrate how to use the real data presented by NTEP or individually by Universities such as here in Minnesota. Remember the LSD statistic indicates what the minimum difference is between the averages of the different varieties for them to be considered truly better or different than the others. In this case, all of those varieties separated by a difference of less than 1.3 would be considered similar in their turfgrass quality even though they may not have exactly the same average value. Thus, in our example, varieties A, G, Y, B, M, and J would all be considered similar in turfgrass quality. Hence, there should be little to no difference among the first six varieties relative to overall turfgrass quality.

In general, you work from the top down when determining LSD groupings. It should be apparent that you could start anywhere in the column and create a set of varieties that are not significantly different from each other in turfgrass quality. For example, using our LSD of 1.3, we could justifiably say that varieties M, J, S and C are not significantly different from each other. That would be a true statement but, there would be some question as to how meaningful that particular group of varieties would be. In general, we are looking for varieties that rank at or near the top for our particular characteristic, not necessarily those in the middle of the pack. Hence, the reason for beginning at the top and working down the column rather than working from the bottom up or starting randomly in the middle of the column. One can also use the LSD statistic to compare one variety with another rather than creating a particular group of varieties as was just done in the above example.

UofMN Newturftrials install(2)_med.jpg

Photo 2: Early growth of new U of MN turfgrass evaluation study. Bob Mugaas.

Our own University of Minnesota Turfgrass Program website,, also has variety evaluation information. Likewise the evaluation data presented in our various research reports is arranged in the same manner as that of NTEP and utilizes the LSD statistic to separate significant differences between particular cultivars or groups of cultivars. Thus, if you would like to know how particular turfgrass varieties performed in this area, check out this website for that information as well as other information about the University of Minnesota Turfgrass program.

Hopefully, this information will encourage you to do some investigating into the turfgrass varieties that have the potential to perform well in this area and in your particular situation. Next month, we'll discuss understanding a grass seed label and what to do when the varieties you're looking for aren't listed on any of the packages of seed you've examined.

How well do you know your Minnesota lawn grasses?

Bob Mugaas, University of Minnesota Extension Educator

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Photo 1: Springtime lawn and landscape. Bob Mugaas.

One of the favorite winter pastimes for Minnesota gardeners is looking through seed and nursery catalogs that in turn, fuel one's desire to plant and try new vegetables, flowers, trees or shrubs in the coming year. But, this is also a good time of year to plan ahead to repair or replace those lawn areas that may not be doing so well. If you are thinking about just trying to thicken up your lawn or perhaps even introduce some different types of grasses into an existing lawn to improve such things as drought tolerance, disease resistance, shade tolerance or lower the need for inputs of water and nutrients, this is also a good time of year to do some homework on the best grasses to use to achieve those goals.

A good planning exercise for the winter is to look out your windows and try to reflect on whether or not the lawn seems to be doing well in those areas. If not, make a note of what seemed to be the problem and try to determine why the grass may not be doing so well in those areas. For example, has the amount of shade increased due to the growth and canopy expansion of landscape trees? Or, has the shrub border grown and enlarged such that it has increased shading of the adjacent lawn area? Both of these conditions can cause a thinning and overall decline of the lawn. In this case, some tree and/or shrub pruning may be needed to provide some additional light and better air circulation to the area. Hence, with an improved growing environment for the grass plants, reestablishment success will be more likely.

As another example, an area may be thinning due to excessive play and use that has resulted in significantly compacted soils and consequent weed invasion. Making note of problem areas and possible causes for lawn decline will help determine appropriate turfgrass species and varieties to use as well as what other repair strategies may be needed. Spending some time making these assessments now will make the implementation of a repair plan during the busy spring gardening period much easier to carry out.

Now, on to our lawn grasses. In this part of the country, we are very fortunate to have several lawn grass species to choose from that can meet most anyone's lawn goals and expectations. Following is some brief information about the three primary lawn grasses used in Minnesota: Kentucky bluegrass, fine fescue and perennial ryegrass. If you would like a more comprehensive review of these (and other) species, see the home lawn care section chapter on selecting grasses in the Sustainable Urban Landscape Information Series website:

Kentucky bluegrass (Poa pratensis)

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Photo 2: Kentucky bluegrass. Bob Mugaas.

Kentucky bluegrass remains the most popular lawn grass planted in Minnesota and is almost exclusively used in the production of sod for this area. See Photo 2. It's widely used in home lawns, parks, athletic fields and golf courses. Varieties of Kentucky bluegrass range from medium to dark green in color. Most varieties require higher maintenance (water, nutrients, etc.) levels to remain healthy and vigorous and most will not perform well in shady conditions.

Kentucky bluegrass grows and spreads by producing underground stems known as rhizomes that send up shoots as they grow through the soil. This allows Kentucky bluegrass to more rapidly recover from injury and abuse than any of the other lawn grasses and be very competitive against weed invasion. This is also the primary reason why this species is so popular with sod producers.

The tip of an unmowed Kentucky bluegrass leaf is shaped like the front end of a typical fishing boat, hence the designation of having a 'boat-shaped' leaf tip. This is a very reliable identification characteristic for Kentucky bluegrass and can help to easily assess where and how much Kentucky bluegrass is growing in a home lawn.

Fine Fescues (Festuca spp.)

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Photo 3: Leaf texture comparison of fine fescue and Kentucky bluegrass. Bob Mugaas.

The term "fine-leaved fescues" is generally applied to three similar species commonly used in our lawn mixes. They are strong creeping red fescue (Festuca rubra spp. rubra), chewings fescue (Festuca rubra var. commutata) and hard fescue (Festuca longifolia). Occasionally, sheep fescue (Festuca ovina) is utilized in mixes to be used in very low-maintenance areas and 'no-mow' mixes. Strong creeping red fescue does spread by rhizomes but is not nearly as aggressive as Kentucky bluegrass. Chewings fescue and hard fescue are considered bunch-type grasses as they lack rhizomes or stolons and spread primarily by tillering. They are both considered excellent choices for home lawns. Fine fescues are not normally available or grown as sod.

 As their name implies the fine fescues are very fine textured grasses. See Photo 3 for comparison of fine fescue leaf texture with that of Kentucky bluegrass. They are also characterized by medium to slow growth rates and medium to dark green color. Fine fescues have lower maintenance needs (i.e., less water and nutrient inputs) including some that have reduced mowing requirements. They have good drought tolerance and adapt well to the shadier areas in the landscape, particularly dry shade. Their wear tolerance is not as good as that of Kentucky bluegrass or perennial ryegrass. Likewise, fine fescues will tend to do better in lawns receiving lower levels of lawn care inputs while Kentucky bluegrasses will perform better at moderate to higher lawn care inputs levels. Thumbnail image for Picture 6.JPG

Photo 4: Fine fescue no-mow mix at UMORE Park. Bob Mugaas.

The fine fescues are frequently mixed with Kentucky bluegrass for average home lawn conditions. In a mixed landscape where there are some areas of full sun and some areas of partial shade, the fine fescues will usually tend to dominate in the shadier areas while the Kentucky bluegrasses will be more dominant in the sunnier areas. Fine fescues, particularly hard and sheep fescues, are usually major components of mixes sold as 'no-mow' mixes. See Photo 4 for example of a two year old no-mow mix growing out at UMORE Park in Rosemount, MN. These mixes have been increasingly popular choices where mowing is not able to be done on a regular basis or site conditions make mowing unsafe. No-mow mixes have also been used to create a transition zone from natural plantings such as prairie or woodland gardens to maintained lawn areas. Their slower growth rates and limited spreading ability help prevent them from aggressively invading into these natural areas.

Perennial ryegrass (Lolium perenne)

Perennial ryegrass is a cool season, medium-textured, bunch-type grass. It is a higher maintenance requiring grass that can withstand the higher amounts of wear and tear common to areas such as athletic fields or intensively used backyards. Its biggest drawback is its lack of cold hardiness. It is the least hardy of the three major lawn grasses used in this area.

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Photo 5: Perennial ryegrass. Bob Mugaas.

Perennial ryegrass usually has a dark green color with a texture similar to that of Kentucky bluegrass. See Photo 5. Hence, perennial ryegrass makes a good seed mix component with Kentucky bluegrass when used for higher maintenance / higher use lawns and recreational areas.

Perennial ryegrass can usually be identified by its shiny green color on the underside of the leaf blade while the upper surface has a rather dull, flat green appearance. The mid-vein of the leaf is also visually quite prominent on the upper side of the leaf.  The leaf tip comes to more of a point rather than the 'boat shaped tip' common to the bluegrasses. The lower portion of the perennial ryegrass shoot is usually dark red to purplish colored as opposed to Kentucky bluegrass which is a lighter green to nearly whitish at the base of the shoot.

Perennial ryegrass is well known for its quick germination and vigorous seedling growth. Those characteristics make it particularly valuable when rapid repair and establishment of a turfgrass cover is desired. A drawback of that characteristic is that it can quickly shade and overpower slower germinating Kentucky bluegrass and fine fescue seedlings when sown at the same time. Ultimately, this can result in very low populations of Kentucky bluegrass and fine fescue getting established in the lawn. With the hardiness problems associated with perennial ryegrass, severe winter injury could result in a very thin lawn the following spring with a consequent need for significant reseeding to be done. Nonetheless, small amounts (< 20%) of perennial ryegrass in a home lawn seed mix will help get some early establishment on the site and provide some protection of the slower germinating grasses.

More Next Month

That's it for now. Next month we'll explore a couple of other grass species occasionally encountered in seed mixes for this area. There will also be some information about specific turfgrass variety selection and what to do when you can't find them at your local garden center or other retail outlets. Until then, take some time to do a little lawn care reflection and planning along with enjoying the many seed and garden catalogs that all help, once again, create enthusiasm for this coming growing season.

Cottony Grass Scale: A Year Later

Bob Mugaas, University of Minnesota Extension Educator
Jeffrey Hahn, Asst. Extension Entomologist


Photo 1: Close up of cottony grass scale. Jeffrey Hahn.

This past year saw a significant increase in the number of reported cases of cottony grass scale (CGS), Eriopeltis festucae, in Minnesota lawns. In 2007, we were only aware of one reported case of cottony grass scale. By 2008, that number had grown to about 6 newly reported cases with the one from 2007 disappearing entirely as there were no signs of infestation in 2008. However, by the end of September in 2009 the number of reported cases that we knew about rose sharply to between 75 and 100. While these were reported cases and not necessarily confirmed infestations, most recognized and described the symptoms, and ultimately the insect, as that shown in our previous article first describing this insect in Minnesota. (See the December 2008 YnG newsletter). Hence, it appears reasonable to assume that most identifications were likely correct.

In order to get a better feel for the scope and range of this insect in Minnesota, it was decided to conduct a survey of those reporting CGS infestations to us. The survey was conducted with with potential participants notified via email that the survey had been posted followed by a request that they take a few minutes to complete the survey. All respondents and responses were kept anonymous. 

The survey covered a variety of topics ranging from symptoms observed, site conditions where most commonly found as well as cultural and pesticide practices employed to manage and control the pest. Sixteen respondents of about 18 receiving the questionnaire completed the on-line survey. This article summarizes those results as well as provides an update to last year's article concerning CGS In Minnesota. 

While our awareness of this pest was first noted in 2007, one survey respondent reported seeing it in 2006 although we are not certain as to its location. In 2007 and 2008 all of the reported infestations were from around the greater Twin Cities metropolitan area. In the survey, CGS was reported in just two sites in 2007 and only nine sites in 2008. In 2009, reports of CGS infestation had expanded to include many Twin City municipalities as well as reports from border counties in western Wisconsin, Mankato, St. Cloud, Brainerd and Alexandria. There may be other locations as well. However, we only have confirmed documentation from those particular areas. In the survey, CGS was observed at 63 - 78 sites. It is unclear why this dramatic increase of reports occurred. 

We were very interested to learn if CGS was successfully surviving winters. Of the single site in 2006, the 2 properties in 2007, and the 9 lawns in 2008, CGS was observed on all of same properties the following season. Although not reflected by the survey, we are aware of at least one property where CGS has not been found in two years since it was first found in 2007. Still, this suggests that CGS are capable of surviving winters in Minnesota.

Typically, CGS is observed in August or September, although in a few cases it was noticed in June and July. Late summer coincides with when CGS matures into adults and produces egg sacs. These stages are much more conspicuous as a white woolly material surrounds the insect, making them much easier to see in the grass. The life cycle is still not well understood but this species is reported in the literature to overwinter in Maine in the egg stage. That appears to be true in Minnesota.


Photo 2: Typical mower wheel track striping pattern associated with CGS when mowed in one direction. Bob Mugaas.

As was noted last year, the most common symptom associated with CGS is the distinctive mower pattern in which the wheel tracks consistent with those of a commercial riding mower remain green and mostly non-infested. This creates a striped pattern where grass is mowed in only one direction or a checkerboard pattern where grass is mowed in two directions and at right angles to each other. See Pictures 2 and 3. The area below the mowing deck varied from light to very heavy infestations of CGS with the corresponding yellow to tan grass blades associated with their feeding. Only two of sixteen respondents reported an infestation that did not show-up in that same pattern. In one of those instances a walk behind rotary mower was used as opposed to a commercial riding type of mower.Picture2.JPG

Photo 3: Mower wheel track striping pattern associated with CGS when mowed in two directions perpendicular to each other. Bob Mugaas.

While that sort of mowing pattern suggests that the insects may be being destroyed via a crushing action imparted by the riding mower, it remains uncertain as to whether or not, or how much of that really occurs. Further evidence gleaned from the survey that some type of crushing action is occurring was noted by three of the survey respondents. In one instance, a respondent noted that when the area was rolled using the roller on a lawn aerifier, the lawn improved dramatically within two to three weeks. In another instance, the infested area was rolled with (presumably) something like a sod roller where it was again noted that the lawn recovered 'rather quickly'. In this last case the rolling was done when the cottony, cocoon-like grass scales were present and visible on the grass blades. One respondent noted that by not mowing in the same wheel track pattern each time, thereby destroying another portion of the CGS infestation, recovery of the turfgrass was evidenced by improved green color. See picture 4. 


Photo 4: Comparison of infestation levels in areas associated mower wheel track and not mower wheel track areas. Note lack of infestation in greener, wheel track areas compared to areas in between wheels. Bob Mugaas.

To the best that we can interpret from survey information, all of the rolling/crushing activity would have occurred when the cottony, sac-like structures were clearly evident. While the above observations are very important in helping us better understand the potential vulnerability of CGS, it is hoped that further investigation and observation will help clarify the specific association with mower wheel tracks and the presence or absence of this pest in those specific, rather narrow areas. 

Previous information provided by people encountering this problem indicated that it was primarily found on more highly maintained lawns presumably dominated by Kentucky bluegrass and for the most part receiving full sun exposure. As a follow-up to that anecdotal information, the survey asked respondents to identify the lawn care situations where this pest was being observed. Their choices were as follows:

  • Highly maintained lawns (e.g. regularly mowed, fertilized at 3 to 5 pounds of N per 1000 square feet annually, irrigated, kept green throughout the year)
  • Moderately maintained lawns (e.g. regularly mowed, fertilized at 2 to 3 pounds of N annually, irrigated as needed to keep lawn basically green but some browning tolerated)
  • Low maintenance lawns (e.g. mowed as needed, not irrigated at least with any degree of regularity, fertilized with 1 or 2 pounds of N annually, brown grass associated with summer dormancy is tolerated)

Twelve of the sixteen respondents indicated that this was a pest primarily infesting more highly maintained, Kentucky bluegrass lawns thus lending credence to what others were saying as well as our own observations. Only three indicated a presence on moderately maintained lawns and only one respondent noted CGS presence on a low maintenance lawn. While not asked directly in the survey, personal observation of infested sites along with input from others indicated that this pest is not as attracted to the fine fescue (only two reports) lawn grasses. While their presence was noted on the fine fescues it was in much smaller numbers than that observed on Kentucky bluegrass. In another sighting, it was observed that the creeping bentgrass growing in the same area as Kentucky bluegrass was not infested while the surrounding Kentucky bluegrass was heavily infested. See Picture 5. 


Photo 5: Note non-infested creeping bentgrass compared to surrounding Kentucky bluegrass. Here Peter Fanjul.

From this limited amount of field observation, it would appear that well maintained, predominantly Kentucky bluegrass lawns, are more likely to be infested with CGS than those lawns receiving moderate to low levels of maintenance. With this being a relatively small sample size, further observation and monitoring will help confirm any turfgrass species preferences of this pest. While the level of sunlight received by the infested areas was not specifically asked in the survey, it would generally be assumed that an otherwise healthy, more highly maintained Kentucky bluegrass lawn would be located in an area receiving full to mostly sunlight conditions. However, there are at least two reports, one from the survey and one not, that did observe CGS in partially (tree) shaded areas of the lawn. In light of where this pest appears to occur most frequently, it would appear that its preference would be for actively growing Kentucky bluegrass in mostly sunny areas. However, its occurrence in more shaded situations cannot be ruled out. Again, future monitoring and observation should help clarify site and plant material feeding preferences of CGS.

Another aspect of CGS management that the survey helped assess was whether or not the implementation of any particular cultural practice or change in cultural practice helped improve the turfgrass stand (i.e., symptoms abated and grass color and vigor improved). Ten of sixteen respondents tried making at least one cultural practice change compared to what was previously being done. Those cultural practices asked by the survey included:

  1. use of more or less water
  2. use of more or less nitrogen
  3. mowing heights increased or decreased
  4. mowing frequency less often or more often
  5. lawn dethatched only, lawn aerified only or, lawn dethatched and aerified.

Four of the ten respondents who indicated the implementation of at least one cultural practice change noted that the lawn improved following those practices during the same growing season. Two respondents reported no improvement. 

There was no clear pattern of practices that seemed to be any more helpful than another. For example, the one respondent who indicated that they 'aerified only' reported improvement in the turfgrass similar to two respondents who utilized four different practices including the use of aerification. Of the two respondents that increased water or chose to mow less often, both indicated seeing no improvement in the turfgrass. A respondent who indicated an increase in N and mowing higher was uncertain as to whether or not the situation had improved. However, that same respondent did indicate that use of Merit alone or with cultural practice changes (presumably those mentioned above) resulted in improvement in the turfgrass stand. When changes in cultural practices were combined with the application of an insecticide, four of six respondents noted an improvement while two noted no improvement. 

While there appears to be a clearer understanding as to this pest's preference for well maintained lawns, it is not as clear as to which cultural practices might be more important in either encouraging or discouraging the establishment of and/or maintaining an existing pest population. Also, there does not seem to be a clear cut pattern of control using pesticides alone or with a particular set of cultural practice changes. For example, of the two respondents who indicated that they reduced water and nitrogen amounts and used an insecticide (Merit), one noted improvement while the other did not. 

Eight people applied insecticides to attempt to manage CGS. Two used Merit and both believed these applications decreased the population of CGS. One applicator also treated his lawn with Talstar (bifenthrin) but did not think it was effective. One respondent used both Merit and Talstar believing that this was effective management. Likewise, one person used Scimitar (lambda cyhalothrin) and thought he gained a reduction of CGS. There was also a single record of acephate although they did not record whether they thought it was effective. Another person used horticultural oil but didn't know whether it was effective. 

It is interesting that the insecticide applications appeared to improve the turf in some cases. Although Merit should be effective, it would not be expected to have an impact on CGS numbers until the following spring. We would not expect any of the residual insecticides (Talstar, Scimitar, horticultural oil) to be effective on adults, although they would be effective against crawlers if you were able to time the application when they were present.

Eight out of nine people that did nothing did not see an improvement in the turf in the same season. There was one respondent that said the turf was looking good again by late October. It will be particularly interesting to observe infested lawns next spring to see whether they have recovered or not. It has been our observation to this point that turf does improve without any lasting injury. With many more properties to examine, this will help us determine if this generally true.

In summary, it is understood by the authors that this survey represents a relatively small number of respondents. Nonetheless, it is an attempt to gather rudimentary yet useful information about CGS presence, habits and control strategies being utilized in Minnesota to manage this pest. It is hoped that our own further observation and monitoring plus valuable input from the lawn care industry will continue to provide an expanding data base on CGS management. From that information, effective IPM strategies can be developed and refined to provide lawn care personnel as well as homeowners with a variety of effective management and control options for CGS.

Dormant Seeding Lawns: Last chore of the season?

Bob Mugaas, University of Minnesota Extension Educator Thumbnail image for Thumbnail image for Thumbnail image for Thumbnail image for Thumbnail image for Picture 1-DS.JPG

Photo 1 (above): Thin lawn area that could benefit from dormant seeding. Bob Mugaas.

One last shot at lawn improvement can be done even yet this fall. By early November, most lawn care chores and activities are completed; lawn mowers are put away, watering has ended, hoses are drained and stored for the winter, irrigation systems have been blown out and winterized and, the last, late season nitrogen fertilizer has been put down.  Yet, there remains one activity that can still be done to help repair or thicken the lawn for next year. In fact, prior to the early part of November (at least in the Twin Cities area, earlier in the northern half of Minnesota), it would be have been too early to do this task. That task is known as dormant seeding.  It is best employed when wanting to reseed bare soil areas or help thicken up thin lawns. It is not as effective, where lawns are thick and dense with little opportunity to achieve the good seed to soil contact necessary for the grass seeds to germinate and grow next spring.

The Dormant Seeding Process

Dormant seeding involves putting down seed while the ground is not frozen, yet cold enough so germination of the grass seed will not occur until next spring when the soils begin to warm. In fact, seeds that do germinate late in the season often do not survive the winter because the very young, immature seedlings have a difficult time surviving those harsh conditions. Other than the time of year of dormant seeding, the actual process of preparing the area to be seeded is virtually identical to establishing grass from seed at other times of the year.

Choosing Well Adapted Seed

When choosing the seed to use, be sure to select seed mixes that are well adapted to both your site conditions and the amount of maintenance you expect to provide during the growing season. For average lawn conditions, mixes containing some Kentucky bluegrass, fine fescue and small amounts of perennial ryegrass can be sown about three to four pounds per 1000 ft2.

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Photo 2 (left and above): Vertical rotating tines of a vertical mower, sometimes termed a power rake. Bob Mugaas.

Establishing Good Seed to Soil Contact

Success of any grass seeding process depends largely on good seed to soil contact. Therefore, the initial step in preparing the area is to loosen the soil surface so the seed can easily be incorporated into the surface half-inch or so of loose soil. Small areas of bare soil or even a thin turfgrass stand can easily be prepared using a hand rake. Larger areas of sparse turfgrass can be prepared by 'lightly' going over the surface with a power rake or vertical mower available from most rental agencies. Set the blades just deep enough to penetrate into the top ¼ inch or so of soil. This will also help remove small thatch layers that may be present, as well as any dead grass plant parts laying on the surface of the soil.

Rake up the grass plant debris that was brought to the surface from this process so that it will not interfere with sowing the grass seed. This debris can easily be composted or used as a mulch in another area of the landscape. Remember these units are NOT intended to be used as rototillers. They are designed and used to remove thatch with only light penetration into the surface soil. Hence, use them appropriately; your rental service will appreciate your proper use of their equipment.

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Photo 3 (left): Using a vertical mower to prepare lawn/soil surface prior to seeding. Bob Mugaas.

Another machine known as a slit seeder could also be used. This machine creates a shallow slit in the soil into which the seed is dropped, lightly covered and packed down. There are some rental businesses that have such a unit available. More commonly this is a practice hired done by a lawn care professional.

Watering Thoroughly, but Not Too Much

Once the seeds have been properly sown and lightly incorporated into the existing soil, water the area thoroughly and leave until next spring. By this time of year, our cool to cold temperatures and short days will help keep the areas moist far longer than in summer. While just barely damp soil is okay, it is important that the area does not become soggy and saturated with water. If the weather does turn a little warmer and drier and the area starts to dry out,  it may be necessary to lightly water the area just to keep it damp and prevent it from becoming too dry.  However, in most cases it will be unnecessary to do this.

What to Expect for Next Spring

Above are the essentials for the process known as dormant seeding. The degree of success from your dormant seeding efforts will depend on the overwintering conditions afforded to the newly seeded areas. In most cases, the seed is best protected when we receive snowfall(s) that will cover and protect those areas during fluctuating weather conditions often experienced during a Minnesota winter. Even with good preparation, it may still be necessary to do some overseeding in the spring in those areas where little grass emerges. If the newly seeded areas appear to be a little thin, you shouldn't necessarily feel your fall efforts were a failure, as it is quite common to have to do a little additional reseeding in the spring. However, do allow enough time for the seeds to come up the following spring. Don't be too hasty to get in and start tearing things up; you just may be destroying all of the good work done the previous fall.

For those of you who postponed doing some lawn seeding earlier last summer, consider doing some dormant seeding yet this fall. It may be just the ticket to give you and your lawn a jump start next spring.

Lawn Care Tips for October

Bob Mugaas, University of Minnesota Extension Educator

Thumbnail image for 10-1-09picture 1_cropped_ bobmugaas.jpg1.Cease lawn mowing when temperatures are cool to cold and the grass shoot growth has essentially stopped. Reducing mowing heights to 2.0 - 2.5 inches for the last two or three lawn mowings of the season will reduce the amount of leaf tissue present over winter and can reduce the amount of snow mold that may occur. It is not necessary to collect clippings as long as they can filter down into the turfgrass canopy at the soil surface. Excessive amounts of grass clippings should not be left on the lawn surface in the fall or at any other time of the year.  Photo 1 (left). Lawn mowing should continue through the fall. Bob Mugaas.

2. A thin layer of leaves can be left on the lawn as long as they are ultimately chopped up as the lawn is mowed through the fall.

3. When confronted with several inches of leaves over the lawn, it is best to rake off the majority of those leaves before mowing and either compost them or use them as mulch material in other parts of the landscape. Thumbnail image for Thumbnail image for 10-1-09picture2_bobmugaas.JPG A thick layer of leaves left on the lawn blocks out sunlight to the grass and may even smother the existing grass beneath that layer resulting in large areas of thin or even dead grass come next spring. Photo 2 (left): Acceptable leaf cover that can be ground up adequately with a lawn mower. Bob Mugaas

4. Early October can still be an excellent time for controlling those pesky perennial broadleaf weeds such as dandelion and creeping Charlie.  Best control with most available herbicide products is achieved when daytime temperatures are above 50o F. but less than about 80o F. That's usually not a problem at this time of year.  Be sure that neither the grass nor the weeds you are intending to treat are under any drought stress. Drought stress will usually result in less than satisfactory control and may even injure the desirable lawn grasses because they can become susceptible to broadleaf herbicide injury under such circumstances. Always follow product label directions for proper use whether in the fall or any other time of the year.  Photo 3 (below and right). Young and mature dandelion plants are best controlled in the fall. Bob Mugaas
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5. In the Twin Cities, a late season application of nitrogen fertilizer should be put down around Halloween.  At this time of year, the nitrogen is taken up into the plant and stored in the crowns, rhizomes, tillers and/or stolons where it can be quickly accessed next spring by the growing grass plant. Follow this application with about ¼ to ½ inch of water to move the nutrients into the soil where they can be taken up by the roots. Never apply fertilizer to frozen ground. You would like about two to three weeks of unfrozen ground following this fertilizer application to allow for root uptake of the nutrients.

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6. As a general rule-of-thumb, it is best to avoid stimulating excessive shoot growth during late September to mid-October. Succulent growth associated with higher nitrogen levels, can contribute to increased incidence of snow mold over winter. A fertilizer application about the time of the State Fair provides the additional nutrients for the fall growth period, while the late season application is primarily stored for growth next spring. It is often easy to tell which lawn has had a late season application of nitrogen as they will usually be noticed as the first lawns with healthy growth and a dark green color in early spring. Photo 5 (above and left): Photo taken in early May. Dark green strip received a late season N application the fall before; surrounding turfgrass area did not. Bob Mugaas

 7. With the current dry period we are experiencing, regular watering should be continued throughout the fall period or until more frequent rainfall returns. While you may not need the one inch of water per week as during the summer months, applying that same amount during the fall may be sufficient for two or perhaps even three weeks depending on weather.10-1-09picture7_bobmugaas.JPG Late summer and the fall period are a naturally active growth period for our lawn grasses. Making sure they have ample water and nutrients during that time will aid their recovery from summer stresses and encourage healthy growth for the next growing season. Photo 6 (left). Lawn watering. Bob Mugaas.

Any reseeding of the lawn should have been completed by mid-September in the Twin Cities area. It is best to avoid seeding during the early to mid-October period, as the very young seedlings that do emerge often have poor survival over the winter. If you would still like to do some seeding, you can do what's known as dormant seeding. Before the ground is frozen, but while the soil is cold (so as to not encourage seed germination in the fall),  incorporate the seed into the soil surface. Incorporating the seed into the soil surface will help protect it through winter. Seed remaining in that 'dormant' condition until next spring, can get a head start on germination and growth for the next growing season. In the Twin Cities area, dormant seeding is usually done in early to mid-November depending on weather conditions

With a little effort and planning this fall, successfully preparing the lawn will help it survive the upcoming winter months, while also encouraging a healthy start for next spring. It may seem a little backwards, but preparation of a healthy spring lawn begins the previous fall. For additional information on any of the topics mentioned in this newsletter, please see the lawn care section in our Sustainable Urban Landscape Information Series website at

Lawn care checklist: late summer - early fall

Bob Mugaas, University of Minnesota Extension Educator


Fall lawn care cultural practices employed during the active fall growth period of our grasses can be some of the most important and beneficial activities for your lawn. These practices will aid in good winter survival, early spring green up and growth, as well as provide many other helpful benefits.

Photo 1: Bluegrass lawn recovered from early season drought stress. Bob Mugaas.

With the return of rainfall and moderate temperatures, many of our lawns have come back to life after drier than normal conditions during May, June and early July. With that regrowth beginning, now is a good time to start getting your lawn in tip top shape for the active fall growing period. Below are some good cultural practices to consider.

Seven fall lawn care practices to consider

1. Overseeding and sodding: If the lawn did suffer some permanent injury during the dry conditions of late spring and early summer, now is a good time to do some overseeding or resodding to repair those areas. The very best time of the year to sow grass seed is from about the middle of August to the middle of September in the Twin Cities area. To help ensure a successful overseeding, lightly work the seed into the soil and then keep the area uniformly damp, NOT SOGGY, until seeds start to germinate and emerge from the soil. As the new grass plants get taller and more established, watering can be done a little less frequently but with more water applied per application.

2. Fertilizing: The period right around Labor Day is an excellent time to put down an application of fertilizer. Putting down about one pound of actual nitrogen at this time of year helps provide the plant with the necessary available nitrogen needed to support and sustain active grass plant growth through the fall period. Taking a soil test will help determine whether or not you need either of the other primary nutrients, phosphorus or potassium. Find University of Minnesota Soil Testing Lab at: Remember, it is a violation of Minnesota state law to apply phosphorus containing fertilizers to your lawn unless a soil test indicates there is a need for the nutrient or you are (re)establishing a new lawn. Additional information about this law can be found at:

3. Watering: As days get shorter, temperatures become cooler, and rainfall occurs on a somewhat regular basis, the need for additional or supplemental watering usually diminishes during the fall period. While an inch of water per week is usually necessary to keep lawns actively growing during the summer months, that same one inch of water may now be sufficient for two or even three weeks depending on weather conditions. Nonetheless, it is important to not severely drought stress a lawn if rainfall is not forthcoming. Periodic watering during the fall will help sustain active growth, allowing the grass plants to make and store food that will help it survive winter and resume healthy growth next spring.

4. Manage mowing height: Maintain mowing heights between 2.5 and 3.0 inches throughout most of the fall period. That will allow for plenty of leaf tissue to be actively involved in making food for the grass plant and a more robust root system that can take advantage of available water and nutrients in the soil. For the last two or three cuttings of the year, gradually reduce mowing heights to about 2.0 - 2.5 inches. This can help in the reduction of snow mold and allow for easier clean up of the lawn surface just prior to colder conditions arriving later in the fall.

5.Lawn aerification: If your lawn has significant compaction problems, the period right around Labor Day and through the early fall is an excellent time to do some core aerification. Lawn aerification machines are usually available through most rental businesses.
Photo 2: Lawn aerifier. Note the hollow tines for removing soil cores. Bob Mugaas.

Be sure to rent a core aerifier, one that actually pulls cores out of the soil and redeposits them on the lawn or soil surface. The extra aeration in the soil will encourage more active root growth as well as benefit the soil microbial community. Healthy plant roots and a healthy soil microbial population make for a healthy, vigorous grass plant better able to withstand stress along with normal wear and tear of lawn activity. The cores can be left on the soil or lawn surface to naturally decompose. This will also help control the buildup of thatch in the lawn. It is best to make two or three passes over the lawn to increase the number of holes needed to maximize the benefit.

6. Thatch control: Occasionally, a thick layer of brown fibrous material will build-up between the soil surface and where the grass plant shoots begin to turn green. This brown fibrous mat is known as thatch. It is actually composed of both living and non-living material. Thatch develops from the regular sloughing off of plant roots and other dead and decaying parts of the grass plant. It is however, NOT composed of any grass clippings. While there may be some grass clippings left on the surface, they are not part of the true thatch layer. So, whether you pick up your clippings or not, it will make no difference on the build-up of thatch. The living component of thatch consists of some roots, rhizomes and, of course, the many microorganisms and other living creatures.

If thatch develops at a faster rate than can be broken down by microorganisms, it can accumulate to undesirable levels. Generally, thatch greater than half-inch is undesirable. Cultural practices that contribute to thatch buildup are excessive nitrogen fertilizer, overwatering, infrequent mowing, compacted soils and simply the genetics of the particular grasses. Some grasses are more prone to thatch build-up than others.

Photo 3: Vertical mower or dethatcher; sometimes referred to as a power rake. Bob Mugaas.

Late summer (i.e., early September) is a good time to work at removing excess thatch build-up. Machines know as vertical mowers or de-thatchers can be rented and used to mechanically remove some of the thatch build-up. Leaving the soil cores on the surface will also help begin to break down thatch. In fact, where very thick thatch layers exist, using both a vertical mower and core aerifier may be helpful. If this is the case, thoroughly aerify the lawn, than perform vertical mowing. This operation can be done back to back on the same day if desired. It's a good idea to follow-up with a quarter to half-inch inch of water to reduce lawn stress incurred from the dethatching and aerification processes.

 7. Broadleaf weed control: The month of September into early October is an excellent time for controlling those pesky broadleaf perennial weeds such as dandelion and creeping Charlie. There are many different broadleaf weed control products available that can be used around the home. Always follow the product's label directions exactly as printed on the container. Remember, it is a violation of federal law to handle or use any weed killer inconsistent with its label directions.

9-09_04lawns.jpgPhoto 4: Creeping Charlie growing in a partially shaded lawn area. Bob Mugaas.

Most broadleaf weed killers work best between the temperatures of 50 degrees F and 80 degrees F. Late summer and early fall is an especially good time as these perennial broadleaf weeds are actively growing and the material is moved throughout the plant and root system, resulting in better control. While you may not see the weeds completely dying this year, chances are that few, if any, will be around come next spring.  For more information about many other common lawn and landscape weeds and how best to control them, check out the section: 'Is this Plant a Weed?', on the Gardening Information web page ( .

Helping Lawns Cope with Summer Stresses

Bob Mugaas, University of Minnesota Extension Educator

Irrigation can help reduce drought stress. David Zlesak.

Each summer, temporary periods of hot, dry conditions commonly occur in this part of the country.    Each summer these conditions prompt many questions about caring for and watering our lawns (as well as other landscape plants).   Following are some lawn care tips to help cope with these dry conditions during Minnesota summers.

1.  Where lawns are maintained in an actively growing condition, keep mower heights of cut between  2.5 to 3.0 inches  to encourage deeper rooting.  The cool season lawn grasses common to this area have naturally shallower, less robust root systems during the middle of the summer compared to the spring and fall periods of the year.  Shorter mowing heights without an accompanying increase in water can make that situation even worse and unnecessarily stress the plants.

Water-Wise Gardening


Julie Weisenhorn and Kathy Zuzek, Director, University of Minnesota Master Gardener Volunteer Program & University of Minnesota Extension Educator

Watering your garden and lawn… it seems so straight forward. When the soil is dry or a plant wilts, water. If it doesn’t rain for two weeks, water. If you happen to have the hose on, sprinkle on a little water.

Not so. There are many factors – the type of soil and the amount of sun and wind in your yard, the types of plants that you grow, weather patterns, and your cultural practices – that play into a landscape’s water needs. The water-wise gardener considers and plans for these factors to produce beautiful landscapes while minimizing water use.

The Cutting Edge Lawn Care Exhibit


Bob Mugaas, University of Minnesota Extension Educator

The Cutting Edge is an educational display that is part of the 2009 Minnesota Landscape Arboretum’s Waterosity Educational Exhibit. The display focuses on how more water conservative lawn grasses combined with some small changes in lawn care practices can reduce water needs and other inputs going into the lawn.

The exhibit features small plots of several lower maintenance lawn grasses that are starting to see greater use in more water conservative lawns. For more information on low maintenance grasses, please visit Cool Season Grass Selection. Additionally, a plot of tall fescue, an up and coming turfgrass species with good drought tolerance and some adaptability to shady conditions, is featured. Prairie junegrass, a native of Minnesota prairies, is also be on display as it would appear in a lawn situation. As it already has very good drought tolerance, this shorter growing native species is currently involved in a rigorous U of M plant breeding program to increase other desirable lawn grass characteristics. In addition to viewing separate species and varieties of lawn grasses, both a no-mow mix and an ecology lawn mix are on display to provide yet another alternative to a traditionally managed lawn. For more information on turfgrass research at the University of Minnesota please visit Turfgrass Science and click on the research tab.

Mid-June Lawncare Tips


Bob Mugaas, University of Minnesota Extension Educator

While this past May went down as one of the driest Mays ever, many areas around the Twin Cities have received some rain during the first part of June. That has both been very helpful for our lawn grasses and has also provided the needed moisture for many of our weed seeds, especially crabgrass to begin actively germinating. In most areas of southern Minnesota we are past the time when preemergent herbicides for crabgrass control will be effective. However, that doesn’t mean control is not possible. Those small crabgrass seedlings can effectively be controlled with postemergent herbicides. One of the newer active ingredients for crabgrass control is quinclorac. This is a very good herbicide for controlling crabgrass once it’s germinated and the seedlings are visible. However, it is usually mixed with other broadleaf control products and marketed for home use as general weed and crabgrass killers. However, it is important to note that with these combination products, you will be applying other herbicides that are not needed or even effective at controlling crabgrass. Hence, this unnecessarily introduces these other materials into the environment; something we try to minimize doing whenever possible.

Early June Lawncare Tips


Bob Mugaas, University of Minnesota Extension Educator

In some areas of the state, lawns have received ample moisture this spring to maintain good growth and color while others have been quite dry; Twin Cities included.  In fact, supplemental lawn watering has already begun in many areas around the Twin Cities.  In most cases, it will take about 1.0 inch of water per week to keep Kentucky bluegrass lawns green and actively growing through the summer months.  One question frequently asked by homeowners is “How do I know how much water my sprinkler or irrigation system is putting out?” 

Late May Lawn Care Tips


Bob Mugaas, University of Minnesota Extension Educator

Usually the middle to end of May is the prime time for putting down preemergence weed killer for crabgrass. In general early in the month is appropriate for the southern 1/3 of Minnesota while later in May is fine for middle to northern sections of the state. But what if I miss the prime window of application, how do I know if it’s too late to apply the product? That’s a good question. For all practical purposes, once the crabgrass seedlings have emerged from the ground it is too late for a preemergence product to effectively be put down. There is one notable exception and that is the preemergence weed killer known as dithiopyr. It is known in the trade by its product name Dimension. It is a common ingredient in many homeowner formulations. This product does provide some control of seedling crabgrass plants up until the 2 or 3 true leaf stage. That is still a pretty small plant. It is important to distinguish between tillers and leaves. Tillers are secondary shoots that also arise from the crown of the plant. See accompanying picture for a comparison of a two to three tiller stage compared to a two to three leaf stage. Applying dithiopyr at the two to three tiller stage is useless. It must applied prior to or at the two to three leaf stage to have any control effect. It should also be noted that dithiopyr will continue to have its preemergence effect once it’s applied as well as very early postemergence effect.

Early May Lawn Care Tips


Bob Mugaas, University of Minnesota Extension Educator

Early May usually finds most Minnesota lawns well into turning green and in need of a first mowing.   Remember that the early part of the grass growing season, late March through the first part of May, is when our lawn grasses produce the best root growth of the year.  Therefore it is important to not be mowing too short as shorter mowing heights reduce the amount and depth of those roots.  Maintaining an average mowing height for around 2.5 to 3.0 inches, even at this time of year, is appropriate.   Those larger, more robust root systems are important in providing the plant with the necessary water and nutrients to sustain the plant through flowering and increase the plants ability to withstand summer stresses.

For average home lawns consisting primarily of Kentucky bluegrass and growing in sunny conditions, early May is a good time to apply that first application of fertilizer.  Usually this will coincide with about the time you plan to mow for the first time.  This will be especially true if there was no fertilizing done the previous fall.  As a rule of thumb, the amount of fertilizer put down should provide about one pound of actual nitrogen (N) per 1000 ft2 of lawn area.  It’s best to apply about ¼ to ½ inch of water following the fertilizer application to help it dissolve and move into the soil where it will be less apt to runoff and be available for plant roots to take up.

Early Spring Lawn Care Tips

Bob Mugaas, University of Minnesota Extension Educator


While the first few warm days of spring seriously tempt one to get out and do something in the yard and garden, patience may be the better virtue. One of the first tasks many people want to do is rake the lawn. Raking is a good idea as it helps to loosen matted down grass, thereby allowing sunlight and air to reach the soil surface. In turn, this helps warm the soil and stimulate grass into active growth. However, trying to do this too early when soils are still cold and muddy will unnecessarily uproot many healthy grass plants and contribute to increased soil compaction. Hence, the gardeners rule of thumb, stay off and avoid working in or on wet, muddy soils, applies equally well to lawns as it does to gardens. When the soil begins to dry out and is no longer soft and muddy under foot, that’s soon enough to attempt raking a lawn. Each lawn will be a little different in how quickly it starts to warm up and dry out. Monitoring your lawn’s condition every few days early in the spring will determine when its okay to be walking on it and raking can begin.

Repairing Spring Flooded Lawns

Bob Mugaas, University of Minnesota Extension Educator


In the early spring before lawns begin active growth (i.e., foliage is still mostly brown) and the ground is still thawing, lawn grasses can withstand several days of being submerged without suffering serious damage. If floodwaters are cold (<60 degrees F.), as they usually are in early spring, lawn grasses can withstand being submerged for even longer periods of time.

Moving water is usually less harmful to lawn grasses than is ponded, stagnant water. Ponding occurs in areas of poor drainage or results from water being left behind in valleys and depressions when floodwaters recede. Spring flooded lawn areas where the water has risen and then receded rapidly often escape serious permanent injury and death.

Low Maintenance Turfgrass Evaluation Study

Research Update - Low Maintenance Turfgrass Evaluation Study – A cooperative project between University of Minnesota Extension and Hennepin County Environmental Services

Bob Mugaas, University of Minnesota Extension Educator art7-1_600px.jpg

Photo 1: Site conditions prior to low maintenance turfgrass installation, spring 2006. Bob Mugaas

Following is a brief report summarizing the results and observations regarding the establishment and growth of selected fine and tall fescue grass cultivars on an environmentally harsh site. It is located in Spring Park, Minnesota on the shores of Lake Minnetonka. Specifically, it is a nearly fully exposed south facing shoreline embankment between the Lake Minnetonka Sheriff’s Water Patrol (SWP) building and the Spring Park public access (PA). The southerly exposure and very poor, sandy to gravelly soil make this an intensely hot and very dry site. There exists a small lilac hedge along the very top (north) edge of the area adjacent to the parking lot. There are also several, poorly formed crabapple, green ash and Russian olive trees located on this site. All are less than 20 feet in height. Information regarding the establishment, longevity and competitiveness of these grasses on this site should be helpful to others managing similar types of sites.

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