Overseeding is the practice of putting more turfgrass seeds on an existing lawn. This may be done only in spots where bare areas have occurred, or over a larger expanse of lawn to improve the density of turfgrass that has become thin.
Within the transition zone, overseeding a cool-season turfgrass into an existing warm-season turfgrass lawn will provide color and active growth during the cold-weather-related dormant period of the warm-season turfgrass.
The same preparation and application procedures are used in this type of overseeding. The seed selection will be based on the species and varieties of cool-season turfgrass that will establish quickly and then transition out easily when temperatures become warmer and re-energize the warm-season turfgrass.
Typically, with bare or thinning turfgrass, 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 starting again with 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, so the lawn’s condition doesn’t continue to deteriorate.
Follow standard Integrated Pest Management (IPM) procedures if weeds, insects or disease are involved. Take steps to rejuvenate the turfgrass to help it weather drought or excess heat. Review your long-term maintenance program and make adjustments if needed in how you mow, fertilize, and irrigate your lawn.
You want to reduce competition from the existing turfgrass prior to overseeding. Reduce the height of cut to the lowest appropriate height for the variety or varieties of your turfgrass species. Do this gradually, if necessary, always following the one-third rule when you mow.
Select the seed varieties and species that will be compatible with your existing turfgrass, 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.
Make sure you understand how to read a turfgrass seed analysis label, so you can make the best choice of high-quality seed for your specific lawn conditions.
You will need good seed to soil contact for the new seed to germinate. Prepare small bare areas for overseeding by hand raking with a leaf rake. Use a light touch, so you break up the soil surface without raking out the existing turfgrass.
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.
There are several options for overseeding larger areas.
You can break up the thatch layer with two or three passes with a power rake or vertical mower. Remove the debris after each pass. Apply the seed with a drop or broadcast spreader; then make one more pass with a dethatching machine to improve the seed to soil contact.
You can use a slit seeder which will cut thin grooves into the soil surface, deposit the seed into the slits, and push the soil down over them.
You can core aerate in three or four different directions, creating multiple holes in the soil for the seed to fall into. By using core aeration you also reduce compaction and allow better nutrient, air and water infiltration and penetration. This will improve growing conditions for the existing turfgrass as well as the new seed.
After aerating, apply the seed with a drop or broadcast spreader. Then cover the area pulling a piece of chain link fencing or an old cocoa mat door mat to break up the plugs of soil you removed and improve seed to soil contact.
Whichever overseeding process you use, follow the management practices for installing a newly seeded lawn, the seed establishment procedures and recommended post-installation management practices.