Fall Maintenance for Cool-Season Grass Lawns

by Wyatt Miller, Agronomy Specialist

Recently the weather has become milder and fall seems to be just around the corner. With these cooler temperatures, cool-season grass lawns will start to pick back up. Summer tends to be the most stressful time on cool-season grass lawns. Excessive heat, pests and poor management often result in thin stands. Early September is typically the ideal time for aerification, fertilization, and overseeding.
Fall is the true beginning of the growing season for cool-season grasses (tall fescue, Kentucky bluegrass, etc.) and is the ideal time to rebuild a lawn after a stressful summer. The disease potential of summer is past and, with summer annuals at the end of their life cycle and perennials preparing for winter, weed pressure is low. Cool-season grasses are ready to go, they just need the nutrients and space to grow. Now is the time to determine what needs to be done to help the lawn recover.
Before any fertilization, seeding and chemical application is made, homeowners need to know the size of their lawn. Determining the square footage is relatively simple, but there is a tool available to help. The Missouri Lawn Fertilizer Calculator – http://agebb.missouri.edu/fertcalc/, provides a link to a map application that can assist in determining your lawn area.
Fertilization the most important fall maintenance practice. Feeding the grass helps it put on “muscle mass” and really start to compete. Fall is the ideal time for fertilizer because there is little concern of increasing warm weather diseases such as brown patch and Pythium blight. Established lawns need at least 1 Ib N/1000 sq ft, with newer lawns needing a little bit more (see the tool mentioned above). Soluble (quick release) forms like urea work, but may be best split into two applications for more constant feeding and should be watered in. If overseeding, a balanced fertilizer maybe be needed at a rate determined by a soil test.
Fall is also the best time for controlling perennial broadleaves with an herbicide. This is because the plants are naturally moving nutrients to the roots for storage and will translocate herbicides to the roots as well. If overseeding is planned this fall, spot applications of glyphosate may be best for small areas since there is a short reseeding restriction time. If using a 3-way mix or triclopyr, it is best to seed now, asses the stand establishment, and apply in mid-October or next spring because of the longer reseeding restriction interval. Always read (and follow) the label of the intended product carefully to determine the potential effect on seeding efforts.
If overseeding is planned, aerification is a great practice to help prepare the seedbed. Aerification creates pathways for water and nutrients to reach the rootzone, as well as, open up the canopy to enable good seed to soil contact. Ideally, a power rake should be used over the area prior to seeding. A core or spike aerifier may be less effective but can also be used if readily available.
Thin stands and bare spots should be overseeded now as fall is the best time for reseeding cool-season grasses. This will also help reduce weed pressure the following year. The only time a lawn should be mowed short is just prior to overseeding. After a low cutting, aerify, spread the seed, lightly rake seed in, fertilize, and irrigate.
Irrigation to establish tall fescue seed in the fall is likely more important than irrigation used in the summer to keep it green. September rain can be variable from year to year, so supplemental irrigation may be needed. Irrigation for establishment should be light and frequent, just opposite of irrigation on established lawns.
For more information on maintenance or renovation of cool-season grass lawns, see MU Guides:

Cool-Season Grasses: Lawn Maintenance Calendar – https://extension2.missouri.edu/g6705

Cool-Season Grasses: Lawn Establishment and Renovation - https://extension2.missouri.edu/g6700