The best time to over-seed cool-season grasses such as tall fescue and Kentucky bluegrass is September. The young seedlings have ample time to mature before crabgrass germinates in the spring and the heat stress of summer sets in.
However, dormant seeding of turf grass can still be done after the fall.
Here are some pointers to help you get started with the dormant seeding of your lawn.
Dormant over-seeding is best accomplished during the winter, any time between December and February. Temperatures are too cold for germination to take place, so seeds will lie inactive until spring. Once warmer temperatures arrive, seeds will jump to life and begin their growth cycle.
As with any seeding program, it is vital to have good seed-to-soil contact. There are several methods that are commonly used to prepare the seed bed for dormant seeding.
One method is to seed when there has been a light snowfall of up to an inch over unfrozen soil. This is shallow enough that bare spots can still be seen. Spread seed by hand on areas that need thickening up. As the snow melts it brings the seed into good contact with the soil where it will germinate and grow next spring.
Another method is dependent on the surface of the soil being moist followed by 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.
Slit seeding or using a verticutter can also be used as long as the soil is not frozen.
Apply the recommended rate of four pounds of seed per 1,000 square feet of area. Do not apply seed starter fertilizer at this time. The grass is dormant and the nutrients are wasted. Wait to apply the fertilizer in May after the grass has begun its growth.
With any of the above methods, seed germinates in the spring as early as possible. Begin mowing the lawn as soon as the existing grass needs it.
The only major limitation to dormant seeding is what herbicides can be applied for weed control. Tupersan (siduron) can be used as a crabgrass preventer on new seedings but is relatively short-lived. Other preemergence herbicides require that the turf be well-established before application. Turf that has been mowed a couple of times is usually considered mature enough for herbicide application.
Bruce Chladny is horticulture agent at K-State Research and Extension-Douglas County. For more gardening information call the Master Gardener Hotline, 843-7058, between 9 a.m. to noon and 1 p.m. to 4 p.m. Monday, Wednesday or Friday.