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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: sjbauer@umn.edu or 763-767-3518

Karl Foord, Extension Educator - Horticulture

Karl Foord

Photo 1: Native bee nesting site on U of MN St. Paul campus

Karl Foord

Photo 2: Native bee leaving nest to forage - nest hole lower right of photo

Karl Foord

Photo 3: Native bee nesting site on Como Ave. St. Paul

Karl Foord

Photo 4: Native bee navigating grass in front of nesting site

Karl Foord

Photo 5: Native bee approaching nest with pollen load

Karl Foord

Photo 6: Native bee nesting site - Purgatory Park, Minnetonka

Karl Foord

Photo 7: Native bees at hole entrances

Karl Foord

Photo 8: Bauer Berry Farm - Champlin, MN; Note each flag represents a single nest

Karl Foord

Photo 9: Nest entrance hole Bauer Berry Farm - Champlin, MN

One of the projects I am engaged in this summer is the identification and location of the nests of native bees. My partner in this effort is Heather Holm, who is the author of a recently published book entitled, "Pollinators of Native Plants". With additional help from Joel Gardner, a bee biologist and graduate student at the University of Minnesota, and Colleen Satyshur, the research coordinator at the Cedar Creek Ecosystem Science Reserve, we have been able to identify a half dozen different nesting sites of ground nesting native bees. These sites have included areas on: 1) the University of Minnesota campus (Photos 1 & 2), 2) the front of an apartment complex on Como Avenue in St. Paul (Photos 3, 4 & 5) , 3) Purgatory Park, Minnetonka (Photo 6 & 7), 4) a pick-your-own blueberry farm in Champlin Minnesota (Photo 8 & 9), 5) a pick-your-own blueberry farm in Maiden Rock, Wisconsin, and 6) a residence in Chaska.

These sites had several features in common. There was a degree of exposed soil and the areas were mostly untended e.g. ignored or left alone. The fact that these areas are undisturbed by human activity is a critical feature. However, this also means that the areas might not meet the standards of tidiness and neatness often embraced by most urban and suburban neighborhoods.

My upbringing left me with the impression that areas with exposed dirt and perhaps a few weeds were the sign of a slovenly, lazy person. One who did not care enough about their own property to maintain the unspoken but expected standard of tidiness. One key aspect of this standard seems to be a weedless dark green lawn.

The lawn is an English invention indicating aristocratic status. In essence a demonstration that the owner could afford to keep land not being used for buildings or food production.

Wealthy families in America began mimicking such English landscaping styles in the late 1700's. The first lawnmowers were invented in the 1830s in England. The subsequent improvement of these machines permitted middle-class families to imitate aristocratic landscapes and grow finely trimmed lawns in their back gardens.

Jump to the 20th century and behold the increased value of a home through landscaping and its most prominant feature - the well manicured lawn. Maintaining such a lawn may require fertilizers, pesticides, and gasoline powered mowing and maintence equipment as well as water, depending on location.

The University of Minnesota Turf program is searching for ways to reduce the environmental impact of lawns through drought-tolerant, slower growing species as just one of their approaches.

It was the interest in native bees and their nesting sites that has had me reconsider the negative associations associated with some open ground and untidy areas. I now consider such areas to be an important and purposeful part of my landscape, as it provides nesting sites for native bees.

For what used to be an eyesore, is now a place of beauty when occupied by our fascinating native pollinators.

Perhaps it is time to reconsider lawns in terms of their benefits and ecological impacts.

Two Early Flowering Plants for Bees

Karl Foord, Extension Educator - Horticulture




Karl Foord


Photo 1: Andrenid bee approaching Golden Alexander's flower


Karl Foord

Photo 2: Andrenid bee on Golden Alexander's flower




Karl Foord


Photo 3: Two different Andrenid species on Golden Alexander's


Karl Foord

Photo 4: Bombus griseocollis on Blue False Indigo

Karl Foord

Photo 5: Bombus griseocollis on Baptisia australis

Karl Foord

Photo 6: Brown-belted Bumble Bee queen on Blue False Indigo

One of the keys to have a great pollinator garden is to have different types of flowers available for the pollinators at different times of the year. Two early flowering favorites of mine are Golden Alexanders (Zizia aurea) and Blue False Indigo (Baptisia australis).

Golden Alexander's flowers are shallow and easily accessed by small bees with short tongues such as the Mining Bees (Andrenid spp.) shown in photos 1 - 3.

Blue False Indigo flowers are much more difficult to access by small bees but are easily accessed and preferred by bumble bees. The bee in photos 4 - 6 is a Brown-belted Bumble Bee queen (Bombus griseocollis).

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: http://blog.lib.umn.edu/efans/ygnews/2013/05/snow-molds-blight-minnesota-la.html. 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: http://docs.mncia.org/public/website/Directory-2014-Sod.pdf
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.

Where's the Redbud Bloom?

Over the past 30 years, Minnesotans have enjoyed many mild winters. But the winter of 2013-2014 was a return to the winters of yore. In many parts of the state, the past winter was the coldest in either 35 or 78 years and it is a winter that will be remembered for long persistent periods of very cold temperatures. The persistent cold allowed deeper than normal frost penetration in soils even though snowfall was heavy and just as persistent as the cold temperatures. No matter what statistics you look at - lowest temperatures recorded in the state, average monthly temperature, number of days Minnesota reported the coldest temperature in the nation, amount and persistence of snow cover, soil frost depth, windchill conditions, number of nights with 0 degrees or lower - they all add up to one long, cold, snowy, difficult-to-live-through winter.
The past winter also took its toll on trees and shrubs. Winter burn on evergreens and salt damage on roadside white pines were severe. With the arrival of spring, cold injury to plants that are marginally hardy in Minnesota showed up. Vegetative damage can be seen in most of the repeat-blooming shrub roses whose canes died back to the ground. These plants are now busy sending up new canes from their crowns. Because repeat-blooming roses produce flower buds on this year's canes, these plants will still be able to bloom throughout the summer.

K. Zuzek, UMN Extension

Photo 1: Eastern redbud flower

D. Hansen, MN Ag. Exp. Stn.

Photo 2: Eastern redbud without flower bud winter injury

Winter injury to flower buds occurred among other plant species. Among marginally hardy plants that have been introduced to Minnesota from warmer climates, flower buds are often less hardy than vegetative parts such as leaf buds and stems. An example of this type of injury from the past winter is being seen on eastern redbud (Cercis canadensis). Eastern redbuds are small trees with lavender pink pea-like flowers that open to cover tree canopies in May before heart-shaped leaves expand. Flower buds formed during the growing season of 2013 should have provided us with beautiful bloom this spring. Some redbuds in the heart of the Minneapolis/St. Paul did bloom. But thanks to our low winter temperatures the more common scenario, especially in suburbs surrounding the Twin Cities and in colder outstate locations, was flower bud mortality and lack of bloom.

K. Zuzek, UMN Extension

Photo 3: Eastern redbud with flower bud winter injury

Redbuds are not native to Minnesota. Their native range extends throughout much of the eastern half of North America. In the Midwest, the range extends only as far north as southern portions of Iowa, Wisconsin, and Nebraska. The species is considered hardy to Zone 5 where average minimum temperatures fall between -10 degrees F and -20 degrees F, meaning it lacks the cold hardiness needed to survive and perform well in almost all of Minnesota. But decades ago a large number of redbud seedlings were planted at the University of Minnesota Landscape Arboretum and Horticultural Research Center. Some of these proved hardy enough for use in Minnesota landscapes. Over the last 20 years, seed from these trees have been collected each year and plants grown from this seed are sold as the Minnesota strain of redbud. Even with the improved hardiness of the Minnesota strain, redbud bloom is not 100% reliable and in the most severe of winters (such as the winter of 2013-14) flower buds are killed by low winter temperatures. Cold injury to eastern redbud flower buds used to be more common so that lack of bloom occurred every 4 or 5 years. With winter temperatures trending warmer over the last several decades, redbud bloom has been so much more consistent that this year's lack of bloom may seem unusual to all but the oldest few generations of Minnesota gardeners.

Mary Meyer, Extension Horticulturist

Mary Meyer

Figure 1: Ostrich fern background, maidenhair fern foreground

Mary Meyer

Figure 2: Gooseneck loosestrife has almost comical flowers

Mary Meyer

Figure 3: Northern seaoats' flowers are pendulous and easily self-seed

Mary Meyer

Figure 4: From left 'Northwind', Warrior', 'Thundercloud', and Cloud 9' Switchgrass


My backyard is at the bottom of a slope that easily floods when we have a 'rain event' of a few inches. The water can even stand in this area for 12-24 hours - fatal for some plants. To make matters worse, the soil is sandy, so when rain is scarce, the soil is bone dry- again fatal again for some plants. I have three tough perennials that have lived well in this area, all of which are shade tolerant: ostrich fern, Canada anemone and gooseneck loosestrife. All three of these plants have aggressive rhizomes that have helped them to live in this difficult site. I believe all of these plants will grow well in USDA Plant Hardiness Zone 3. However, northern seaoats will only live as an annual, but it will self-sow enough to come back each year.

Ostrich fern (Matteuccia struthiopteris) is a tough native fern (photo 1). Some people may think the ostrich fern is too tough, with its rhizomes and substantial root system. I love the soft feathery fronds and the fact that it will tolerate standing water and survive droughts. In the driest years, the plants are shorter, the rhizomes do not spread, and the plants die back prematurely. In wet years, it begins very aggressively and grows into the adjacent lawn. I transplant it to other shady locations where I want it to grow. The fertile fronds are stiff, much shorter and still standing in the spring when I break them off and push them into the ground as a standing border for the sedge planting that is up the hill under the box elder. This acts as a border signaling my husband where to mow the lawn and not the sedges.

Canada anemone (Anemone canadensis) is another tough native that easily can be too aggressive due to creeping rhizomes. However, the tough conditions of this site keep it in bounds. It is a sea of 1-2 foot tall white flowers in the spring. The foliage is often confused with wild geraniums, but the single white flowers have a cluster of yellow stamens, typical of the buttercup family, and lack the beak-like style of geraniums. Canada anemone foliage makes a thick ground cover that competes well with other weeds, even buckthorn seedlings!

Gooseneck loosestrife (Lysimachia clethroides) is a 2-3 foot tall perennial native to China (photo 2). I am adding it anyway because it has lived in this tough situation as few other plants would. It also has aggressive rhizomes. In dry years the plants are short and do not spread at all, while In wet years it is tall and robust. I step on it to keep it in bounds as I go to the compost pile, or edge it with the lawn mower. The gooseneck flowers are fun to look at and a delight in floral arrangements. It is one plant that blooms regardless of weather conditions.

Other plants (grasses are my favorites!) that I could add in this site are:

Wood oats or Northern seaoats (Chasmanthium latiflium) (photo 3) are native to south central U.S. and marginally hardy in zone 4. This grass self-seeds and although one plant may die, another will likely come up on its own. This is a bunch grass, with no rhizomes. It has the best flowers for dried arrangements and will last for years if picked early before the seeds are fully developed. The pendulous flowers are flat and beautiful in the fall when they turn bronze and yellow. This grass is native in wooded areas along river banks and it prefers wet sites where it can grow to 4 feet. In drier sites it may only be 2 feet tall. A newer form 'River Mist' is yellow and white striped, much shorter e.g. 18 inches, and has only lived as an annual for me.

Prairie cordgrass or slough grass (Spartina pectinata) is a larger, 4-6 foot tall, long-leaved grass for wet sites that will tolerate standing water and lakeshores. Native to prairies and often found in roadside ditches, slough grass has creeping rhizomes ideal for binding lakeshores. This grass is large and coarse, good for larger sites. In areas containing only cattails or reed canarygrass, prairie cordgrass can be added to increase diversity. An ornamental form of prairie cordgrass ('Aureomarginata') has yellow stripes on the foliage and creeping rhizomes. Prairie cordgrass prefers full sun conditions, but can grow in light shade.

Native switchgrass (Panicum virgatum) is in almost every roadside ditch across Minnesota. Many ornamental forms are available; we are trialing 17 of these at the Minnesota Landscape Arboretum Grass Collection (Photo 4). Plan to come in September and pick your favorite. The 2014 Perennial Plant of the Year ('Northwind') was selected by the Perennial Plant Association for its 5 foot tall, stiff upright form and olive green foliage. 'Shenandoah' (4' tall) and 'Ruby Ribbons' (2' tall) both have red foliage and flowers. "Cheyenne Sky' is purple and red and grows to 4 feet tall. Most switchgrass plants will tolerate wet soils quite well. They are taller in wet sites and shorter under dry conditions. Switchgrass is a bunch grass and does not have creeping rhizomes, however, it can self-seed readily. Switchgrass prefers full sun conditions and will only tolerate very light shade.

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