You can make your lawn healthier and more attractive by overseeding, which for a cool season lawn involves sowing seeds over existing lawn to cover spots where the grass is patchy. If at least half of your lawn is fairly healthy and strong, overseeding is a good way to revitalize it. In fact, you may want to overseed your cool season lawn every year to keep it looking great. However, if more than half your lawn looks worn out and weak it’s best to start over with a new lawn.
Preparing Your Lawn for Overseeding
If you haven’t had your lawn soil tested in few years do that before you overseed. The test results will give you recommendations for fertilizer or amendments for growing a healthy lawn. Cooperative extension services all over the country provide inexpensive and convenient soil testing.
Grass seed needs sunlight and good contact with soil to germinate and grow. When you sow grass seeds over a lawn the blades of the existing grass shade them, plus thatch and clippings create a barrier between the seeds and the soil. You can help the new seeds by mowing lower than usual before overseeding to reduce shading. Even if you don’t usually remove grass clippings, bag or rake the clippings before overseeding so they don’t interfere with the seeds.
Work the soil lightly with a verticutter or power rake to loosen 1/4 inch of soil. Or use a core aerator to remove plugs of turf and give seeds places to germinate.
If you have protruding roots or rocks you may need to add a layer of topsoil before overseeding. By raking in a 1/4-inch layer of screened loam or topsoil you can increase the depth of the topsoil.
Overseeding cool season lawns in September gives the new seeds time to grow before winter sets in. Tall fescue and Kentucky bluegrass are good turf grass seed choices, either on their own or in mixes. Sow 6-8 pounds of tall fescue or 2-3 pounds of Kentucky blue grass per 1,000 square feet of lawn using a rotary seeder or drop seeder. The tall fescue will germinate in 2-3 weeks, with the bluegrass following a week later.
Apply a slow release nitrogen fertilizer when you overseed. Six-eight weeks later apply a quick release nitrogen fertilizer. Water at least daily to keep the seeds moist until they sprout, then reduce watering after about three weeks.
When the grass is three inches high mow it to two inches and keep mowing it to this height for the rest of the season.
Long after the blades of grass stop growing the root systems of the turf grass will continue to get stronger, in preparation for a lush, green lawn in the spring.