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: http://soiltest.cfans.umn.edu/. 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: https://www.revisor.leg.state.mn.us/statutes/?id=18C.60.
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.
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.
Photo 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 (http://www.extension.umn.edu/gardeninfo/) .