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.
Photo 1: High quality turfgrass. Bob Mugaas
Early May is usually when we see peak dandelion bloom. This often causes people to run out and buy some form of a weed control product to kill them off. However, the real preferred time to kill dandelions is in the fall of the year when the plant is moving food down to the root system to be stored over winter. Nonetheless, there are many available products to kill dandelions even in the very active growth of spring. Be sure to choose a product that is labeled for dandelion control in lawns. Do not use products that are designed to kill all vegetation as they will kill the lawns grasses as well as the dandelions.
Photo 2: Dandelion bloom usually peaks in early May. Bob Mugaas
Weed and feed products designed to apply fertilizer as well as put down a broadleaf weed control product can be effective. However, where there are only a few scattered broadleaf weeds such as dandelions in the lawn you will be applying a lot more product to the lawn than is necessary or effective. You must get the product onto the dandelion foliage as these products do nothing to prevent new dandelions from emerging that start from seed. Thus, if there are only a few scattered dandelions in the lawn, using a pre-mixed, ready-to-use product to spray onto the dandelion foliage is much more efficient and effective. This strategy also introduces far less herbicide into the environment thereby reducing potential pollution and exposure problems.
As soil temperatures begin to warm in the early part of May, we approach the time when crabgrass control products need to be put down. Unlike the broadleaf herbicides mentioned above, these products must be applied before the crabgrass seeds begin to germinate. As the seedling root and sprout emerge from the seed, it comes into contact with the preemergent herbicide and is killed. Frequently this type of herbicide is packaged as a weed and feed product. The fertilizer provides nutrients to help thicken up the lawn grasses, which in itself works to reduce the amount of crabgrass seeds that will germinate and grow. It is a good practice to water in these products with ¼ to ½ inch of water (or rainfall) as soon after application as possible, especially with liquid formulations. This moves the herbicide down to the soil surface where it is bound tightly to the soil particles and provides the desired weed control effect.
Photo 3: Crabgrass is an annual warm season weed that can compete with desired turfgrass species and die in late summer leaving lawns unslightly. David Zlesak
A relatively recent addition to our crabgrass control options is a product known as corn gluten meal. It is a by-product of the corn processing industry and acts like an organic weed-and-feed product. It contains about 9 to 10 percent nitrogen and its preemergent weed control properties were identified and documented through research conducted at Iowa State University. The recommended practice for using this product is to apply it at 20 pounds of product per 1000 square feet of lawn in early May and again early to mid-August. Like the above conventional preemergent products it should also be watered in as soon after application as possible. This product works best when the crabgrass seeds begin to germinate, they contact the corn gluten meal (which in turn damages the newly emerging root) and this followed by a slight drought stress. The inability of the damaged seedling root to supply water to the germinating seed causes it to die. Control usually improves after the first year as the number of seeds available to germinate is reduced plus the added benefits of the nitrogen to improve the turfgrass stand also begin to take effect.
While it may not seem like early spring is a time when we should think about watering our lawns, there are times when it is beneficial for our grass plants. When conditions are warm, windy and dry, both our soils and grass plants can dry out to the point where they can experience varying levels of drought stress. Since spring is a very active period of growth, the less stress encountered the greater the ability of grass to tolerate typical hot dry conditions during the summer months. At those times in early spring when we experience warm, dry conditions, applying about an inch of water to the lawn will be beneficial. If temperatures remain warm to even hot and there is no rainfall, then staying with about an inch of water every 7 to 10 days will help reduce plant stress and keep plants growing actively.