The best time to seed cool-season grasses such as tall fescue and Kentucky bluegrass is September because the turf has more time to mature before spring crabgrass germination and the heat stress of summer. However, dormant seeding of turfgrass is sometimes used to help fill in bare spots of lawns that weren’t overseeded in the fall. Dormant overseeding is done during the winter (December – February) when it is much too cold for germination.
As with any seeding program, good seed-soil contact is vital. Several methods can be used. One method is to seed when there has been a light snowfall of up to an inch. This is shallow enough that bare spots can still be seen. Spread seed by hand on areas that need thickening up. As snow melts, it brings the seed into good contact with the soil where it will germinate in the spring.
Another method is dependent on the surface of the soil being moist followed by some freezing weather. As moist soil freezes and thaws, small pockets are formed on the wet, bare soil that are perfect for catching and holding seed. As the soil dries, the pockets collapse and cover the seed. A third method involves core aerating, verticutting or hand raking and broadcasting seed immediately after. Of course, the soil must be dry enough and unfrozen for this to be practical.
With any of the above methods, seed germinates in the spring as early as possible. However, there will be some limitations on what herbicides can be used for weed control. Tupersan (siduron) can be used as a crabgrass preventer on new seedings even before they have come up. Also dithiopyr, found in Hi-Yield Turf and Ornamental Weed and Grass Stopper, can be used on tall fescue, Kentucky bluegrass and perennial ryegrass two weeks after germination. Dithiopyr is longer lasting and more effective than siduron. Other preemergence herbicides require that the turf be well established before application.