September is traditionally the best time to overseed cool-season grasses such as tall fescue and Kentucky bluegrass. The young seedlings have ample time to mature before crabgrass germinates in the spring and the heat stress of summer sets in.
But with October's mild temperatures and sunny days, gardeners are still asking: "Is it too late to seed my lawn?" The answer is: "Yes and no."
With the threat of frost looming on the horizon, newly sprouted seed will be killed by a freeze. So if you have not planted your grass seed yet, you may want to hold off doing so for a few months because the next best time to overseed is right around the corner.
When the window of opportunity for fall seeding closes, the door for dormant seeding just begins to open. Dormant overseeding is best accomplished during the winter months December through February. Temperatures are too cold for germination, so seeds will lie inactive until spring. However, 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 prepare the soil 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 those areas that need thickening. 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 soil surface being moist followed by freezing weather. As moist soil freezes and thaws, small pockets form that are perfect for catching and holding seed. As the soil dries, the pockets collapse and cover the seed.
Slit seeding or a verticutter can be used as long as the soil is not frozen. Apply the recommended rate of 4 pounds to 5 pounds of seed per 1,000 square feet. 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 started to grow.
Cool-season lawns need to be rejuvenated every year or so. Typically, we do this by overseeding in the fall. However, if you have not been able to check this off your "to do" list, then wait a few months and overseed during the dormant period. The seeds will germinate and grow next spring and you will be well on your way to a healthy, lush green lawn.
Bruce Chladny is horticulture agent at K-State Research and Extension-Douglas County. For more information, call him at 843-7058 from 8 a.m. to 5 p.m. weekdays.