In much of the United States, spring is not the best time to sow grass seeds, but spring weather is beneficial to young grass plants in some parts of the country.
Spring Seeding in the North
In the northern United States, the ideal time to sow grass seeds is in late summer. When grass is seeded at that time of the year, the young seedlings that develop face relatively little competition from weeds, and they're not subjected to the stress caused by the heat and drought of the middle of summer. Seedlings also have time to establish themselves before winter weather arrives.
Spring seeding is unlikely to be successful in the North, but sometimes it's necessary, such as when a new home's construction is completed in the spring and a lawn must be established. If you can't avoid spring seeding, then do it as early as it's possible to work on the soil, preferably in March. Seeding in April or May is riskier.
Cool-season grasses that are most likely to be successful with spring seeding include tall fescue (Festuca arundinacea) and perennial ryegrass (Lolium perenne). Tall fescue is hardy in U.S. Department of Agriculture plant hardiness zones 2 through 7, and perennial ryegrass is hardy in USDA zones 5 through 7.
Spring Seeding in the South
Because the warm-season grass species that fare best in the southern United States are tolerant of midsummer heat, and because spring weather tends to be milder in the South, sowing grass seeds in spring is more likely to be successful in the South than in the North. Sowing in spring, in fact, takes advantage of the spring rainy season; the consistent moisture helps the resulting seedlings get established.
The best time to sow warm-season grass species is in late spring, after the danger of frost has passed, and the window for sowing continues through early summer. Planting too early in areas where frost is a danger risks subjecting grass seedlings to cold temperatures that may kill them.
Warm-season grasses that do well when planted in spring include zoysiagrass (Zoysia spp.) and centipedegrass (Eremochloa ophiuroides). Zoysiagrass is winter-hardy in USDA zones 6 through 9 and centipedegrass in USDA zones 7 through 8.
A seeding technique called "dormant seeding" allows gardeners in the North to take advantage of cool, wet, early-spring weather. In this technique, grass seeds are sown in winter or very early spring, typically between late November and March, when the ground is frozen. Because of the cold soil temperatures, the seeds remain dormant until the soil begins to warm. The seeds germinate early, getting a head-start on the growing season before temperatures start to rise.
Dormant seeding sometimes fails because warm periods in winter or early spring that cause seeds to germinate are followed by a return of cold weather that kills the young seedlings. Because of this possibility, dormant seeding is most likely to be successful in cold-winter climates where extreme temperature fluctuations are not common.