In most parts of the United States, the best time to sow grass seeds is in late summer or early fall. That's because grass seedlings don't fare well in the middle of summer, when high temperatures, scarce moisture and competition from weeds put significant stress on the young plants. Planting late in summer allows seedlings to establish themselves when temperatures are falling and rain is more frequent, and the seedlings will be well-established by the time cold winter weather arrives.
When late-summer seeding isn't possible, a technique called dormant seeding may be an alternative. This technique involves seeding in the winter when the soil and air temperatures are very cold, and it can be accomplished in many U.S. areas between late November and early March.
Advantages of Dormant Seeding
The goal of dormant seeding is to put seeds down when temperatures are cold enough to prevent their germination. The seeds will lie dormant until spring. As soon as the soil begins to warm, though, the seeds will sprout, giving them a good jump on the growing season and allowing them to become well-established before summer's heat.
Cold winter weather also can be advantageous because frost heaving can cause the soil to crack, which can help the seeds settle and achieve better contact with the soil. Snow cover on top of seeds may help to protect them and keep them in place as well.
Disadvantages of Dormant Seeding
Dormant seeding works well only when the seeds are sown during cold weather and when the weather remains consistently cold until spring. Soil temperatures must be below about 50 degrees Fahrenheit to prevent germination, and problems arise when temperatures rise temporarily during winter and then fall again. In those cases, the seeds may germinate during the warm spell only to die when the temperature falls below freezing again.
Because of this potential problem, dormant seeding works best in the northern United States, where winter temperatures are consistently low. It is less likely to be successful in the South. Even in northern climates, exceptionally mild winters with broad temperature fluctuations can cause the technique to fail.
Dormant seeding can be successful with any grass species, but cool-season grasses such as Kentucky bluegrass (Poa pratensis) and tall fescue (Festuca arundinacea) do particularly well when dormant seeded. Both of those species are winter-hardy in U.S. Department of Agriculture plant hardiness zones 2 through 7.