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Fall is a great time of year to consider renovation or over-seeding of the lawn. Cooler weather helps keep the soil from drying out and seeds germinate and establish quickly. Renovations are the replanting of seed or sod into an existing lawn that is thin or died out. It is usually recommended if the current turf is a variety that is frequently attacked by insects or diseases, the landscape has become increasingly shady over time, the turf has been mostly killed out by disease or drought, or a person wants to convert to a new turf species.
Not all thin lawns require renovation. Some may need to have the irrigation system repaired or replaced to improve water delivery to the lawn, or the fertilization schedule may need adjusting to promote better plant growth. If a bunch grass lawn, such as tall fescue or ryegrass, is more than 20 percent thin, it may need reseeding. Bluegrass and other sod forming types that have thinned out to 50 percent of the lawn can be revived with good irrigation and fertilization, but the lawn will fill in more quickly with overseeding.
When starting to renovate the lawn, remove thatch and weeds from the area. After closely mowing your lawn, core aerate the lawn with an aerator and make several passes over it to punch holes not more than 2 inches apart into the soil. Usually, this requires several passes over the area in different directions. Core aeration creates holes into which the grass seed will drop and germinate, unlike weed seeds, which do not germinate well in the aeration holes. As an alternative to using a core aerator, homeowners can use a machine called a slit seeder to sow the seed into the lawn. All of the machinery mentioned above can be found at local hardware stores or equipment rental stores.
If you can, have a soil test to determine if the lawn needs nutrients prior to renovation. After core aerating and before seeding, apply recommended nutrients to the lawn. In the absence of a soil test, use a slow-release fertilizer with an N-P-K ratio of 3-1-2. (Look on the fertilizer bag to find these numbers.)
Apply the seed. Select a blend or mixture of named, improved varieties of lawn grasses. A critical part of successful renovation is to overseed with modern, improved grasses that are insect and disease resistant, and have drought tolerances and sufficient vigor to crowd out weeds. Improved varieties of grass seed will cost less to maintain when you follow proper mowing, watering and fertilizing practices.
Watering the new seeding requires patience. Grass seed may take up to two weeks to germinate, and the seedbed must be kept moist, but not soaked, until the new seeds begin to grow and develop a root system. After 4 to 6 weeks, treat it as a reestablished lawn.
Many lawns will benefit from overseeding now that we have cool, moist weather. A full, lush lawn next spring can be achieved with a little effort and patience now. For further information on lawn renovation and care visit the Colorado State University turf Web site, or contact the Colorado State University Extension office in your county. In Boulder County, the Extension office can be reached at (303) 776-4865.
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