The best time to sow grass seed is when temperatures are moderate and frequent rainfall reduces the need for irrigation to keep soil consistently moist. Planting too early in summer subjects new grass seedlings to the stress of summer's temperature and drought extremes, and planting too late introduces the risk that seedlings will not be established well enough to survive winter.
Ideal Seeding Conditions
In Ohio, that generally means grass should be planted in late summer or early fall, after summer temperatures have peaked and the fall rainy season is about to begin.
Summer and Fall Seeding
The ideal planting time varies. It depends in which part of the state you live. In northern Ohio, where summer heat peaks a bit earlier than in other parts of the state, seeding between mid-August and mid-September is ideal. In the southern part of the state, seeding any time in September will work. Don't seed after Oct. 15 in northern Ohio or after Oct. 30 in southern Ohio.
When conditions don't allow for seeding in the late summer or fall, it may be tempting to seed early the next spring, but spring-seeded lawns are unlikely to thrive. Seedlings will struggle to survive as the weather turns warm and dry, and they'll have a hard time competing with the weed seedlings that will emerge in the middle of summer.
If you must seed in spring, sow seed as early as possible so that seedlings can get established early in the growing season. Seeding before April gives you the best chance of success.
When fall seeding isn't possible, an alternative to spring seeding is winter seeding, which is also called dormant seeding. In this seeding technique, grass seed is sown after the soil temperature has cooled below 40 degrees Fahrenheit so that the seed will not germinate as soon as it's sown. Instead, it remains dormant just until the soil warms in spring, allowing the seedlings to establish themselves very early in the growing season. The time for dormant seeding is typically after Nov. 15 in northern Ohio and after Dec. 1 in southern Ohio.
A common reason for the failure of dormant seeding is a mid-winter warm-up that causes the seed to germinate and is followed by a return to cold temperatures that kills the new seedlings. This situation can lead to seeding failure during exceptionally mild winters with inconsistent snow cover, and it's more likely to happen in the southern part of the state than in the northern section.