Successfully growing a thick, healthy lawn from seed requires an understanding of the needs of different grass species and careful attention to maintenance once the seeds are in the ground.
Turf grass species are categorized as either warm-season or cool-season types, and it's important to choose the type that will grow best in your region. Warm-season grasses flourish in warm weather and do well even when summer temperatures rise above 90 degrees Fahrenheit; they are, however, sensitive to cold and are unlikely to survive in climates with harsh winters. Cool-season grasses are cold-tolerant, but they grow best during cool springs and autumns; they typically go dormant during the hottest part of the summer.
Commonly planted cool-season grasses include Kentucky bluegrass (Poa pratensis), tall fescue (Festuca arundinacea) and fine fescue (Festuca spp.), all of which are winter hardy in U.S. Department of Agriculture plant hardiness zones 2 to 7. Common warm-season grasses include zoysia grass (Zoysia spp.), which is hardy in USDA zones 6 to 9; St. Augustine grass (Stenotaphrum secundatum), which is hardy in USDA zones 8 to 10; and centipede grass (Eremochloa ophiuroides), which is hardy in USDA zones 7 to 8.
In a band across the middle of the United States called the transition zone, which extends from north Texas to southern Pennsylvania and New Jersey, neither warm-season nor cool-season grasses grow particularly well, and lawns in this region may need to incorporate a blend of species for year-round success.
Grass seedlings are most likely to survive and establish themselves when they're protected from the stress caused by heat, lack of water and competition from weeds, and the best way to protect seedlings is to sow seed at the correct time.
When you're planting a cool-season species, the ideal time to sow seed is in the late summer and into the early fall, after the worst of the heat has passed and autumn rains are about to begin. Depending on your specific region, the planting window can extend from the middle of August through the middle of October.
Because warm-season grasses are more tolerant of heat, they can be planted through the summer, but they are most likely to succeed when they're planted early enough in the spring or summer to take advantage of early-season rain.
It's important to prepare the area where you're going to sow seed so that the seed has good contact with the soil. Till the soil to a depth of about 3 inches and rake the area to loosen any clumps of soil. If your soil has a poor texture or is lacking organic matter, incorporate topsoil and compost at this stage. Finish the preparation by going over the planting area with a weighted lawn roller.
After the seed bed is prepared, sow the seed using a garden spreader to ensure that the seed is spread evenly and thoroughly -- spread it in both north-south and east-west directions. The appropriate seeding rate will depend on the particular cultivar you're sowing; some older Kentucky bluegrass cultivars, for example, need to be seeded at a rate of 6 to 8 pounds per 1,000 square feet, while some improved cultivars need only 2 to 3 pounds for the same area.
After the seed is spread, rake to lightly cover the seed with soil; most grass seeds germinate best when they are planted 1/8 to 1/4 inch deep. Roll again to smooth the soil surface and then cover the area with a light layer of straw mulch.
Watering the Seed
Water the seed thoroughly after planting and keep the soil consistently moist until the seeds germinate; during hot, dry weather, this may require watering twice a day or more. When the seedlings are 1 inch high, reduce watering to once a day.
Overseeding is the process of sowing new grass seed over an already established lawn in order to rejuvenate thinning turf or repair bare spots. To prepare turf for overseeding, mow the existing grass to a height of 1 inch and aerate the area with a core aerator.
For best results, use a slice seeder to sow the seed over the turf. This type of seeding machine makes a small furrow into which it deposits the seed, thus ensuring better contact with the soil. The device also allows you to set the planting depth and seeding rate.
After the seed is sown, top-dress the area with a light layer of compost and keep the area moist until the new seed germinates.