Overseeding is the practice of adding grass seed to an existing lawn. This may be done only in spots where bare areas show, or over a larger expanse of lawn to improve the density of grass that has become thin.
Overseeding is a common practice in the transition zone, the geographical area between parts of the country where warm season and cool season grasses converge.
Overseeding a cool-season grass into an existing warm-season grass lawn will provide color and active growth during the cold-weather-related dormant period of the warm-season grass.
Seed selection should be based on the species and varieties of cool-season grass that will establish quickly and then transition out easily when temperatures rise.
Typically, with bare dirt or thinning grass, if 50 percent or more of the existing lawn is in good condition, overseeding can be a workable solution. If more than 50 percent of the area is in poor condition, you will want to consider a new lawn installation.
Bare or thinning problems may be due to damage from heat, drought, disease, weeds, insects, overuse, poor management practices or other factors. It’s best to identify the source of the problem and correct it prior to overseeding. This knowledge will ensure the lawn’s condition doesn’t continue to deteriorate after overseeding. It’s also important to review your long-term maintenance program and make adjustments if needed in how you mow, fertilize, and irrigate your lawn.
You will also want to reduce competition from the existing grass prior to overseeding. Cut the existing lawn to the lowest appropriate height for the variety. Do this gradually, if necessary, always following the one-third rule when you mow (see Mowing for Homeowners).
Select the seed varieties that will be compatible with your existing grass, but have specific performance and/or aesthetic qualities that will improve it. This may be cold, heat or drought tolerance, disease or shade resistance, or simply a deeper shade of green.
You will need good seed-to-soil contact for the new seed to germinate. Prepare small bare areas for overseeding by raking. Use a light touch, so you break up the soil surface without raking out the existing grass.
You can apply seed to these spots by hand or with a drop spreader. Use the recommended rate for your selected seed when overseeding. Rake the area again with the same light touch after you overseed to improve the seed-to-soil contact.
For helpful information on overseeding guidelines talk to the grass specialists at a local nursery, contact a local sod farmer, or visit a university turfgrass extension website for helpful information.