By Katie Winslow, U of M Extension
Although we often think of spring as the time for lawn improvement practices, autumn is actually a better time for fertilizing, seeding, and weed control in lawns. Fall is also the time to determine if dethatching and aerating your lawn is needed. From mid-August through September, assess your lawn’s needs to keep it in tip-top shape.
Early September is the best time of the year to plant grass seed. The grass seed will germinate readily, and the cooler soil will encourage it to develop a good root system that will carry it through the winter. Seeding in the fall allows for grass to establish better than in the spring when grass seed is competing with weed seeds.
When seeding, the soil must be worked up so that the grass seed has contact with receptive soil. If you are seeding small patches, work it up with a garden rake. Larger areas may require the use of a tiller to prepare the soil. After seeding, create a firm seed bed by leveling the soil with a roller or, in small areas, by walking over the seeds.
Next, it is important to water newly seeded areas lightly but frequently. For best germination, be sure there is moist soil to a depth of four to six inches. After seeding, water only as needed; it is not necessary to keep the soil constantly wet. Keep the surface soil moist by watering lightly a couple of times a day and then, as seeds germinate and begin to grow, gradually shift to deeper, but less frequent watering. Stop watering when puddles begin to appear as overwatered, saturated soil leads to root rot and other lawn problems.
It may be advisable to fertilize at the same time you plant the seed using a starter fertilizer. Keep in mind that a soil test should be done before you plant the grass, so that you know exactly what nutrients you will need for continued growth. This is especially important if you have been having issues with your lawn where you plan to plant grass. Do not use any weed-and-feed products where you plan to seed, or on young grass seedlings until the following spring.
When newly planted grass reaches a height of three and a half to four inches, it can be mowed. You can gradually decrease the mowing height as the temperatures cool, but never cut the grass shorter than two and a half to three inches. If you have seeded over an existing lawn, mow whenever the older, established grass needs it.
Early- to mid-September is the time to apply a fall fertilizer to the lawn. If your lawn has a pale green color or is otherwise showing low nitrogen levels, use a standard lawn fertilizer for the September application instead of one of the winterizing formulations.
Remember, September is an excellent time to apply a weed control product to kill perennial weeds that have germinated over the summer. The dandelions that germinated this summer will be your blooming plants next spring. Fall provides an excellent opportunity to control perennial broad-leaved weeds such as common dandelion, creeping charlie, and plantain.
In the fall, perennial weeds move the sugars produced in the leaves to underground roots or rhizomes for the winter and to fuel next year’s growth. This movement of sugars continues as long as the plants are not killed by frost and 50-75% of their leaves are still green and actively growing. Herbicides that are systemic and move within the plant are carried with the sugars to effectively kill the plants in the fall. Although the death of weeds may not be obvious in the fall, most of them will not come back next spring.
For an improved lawn in the spring, use the autumn months to take care of fertilizing, seeding, and weed control. Take caution when using chemicals, and always read and follow the label. For a full lawn care calendar, you can visit www.extension.umn.edu. If you have questions or would like more information about fall lawn care or any other horticultural questions, please call (320) 255-6169 ext. 1.