The best time to plant grass seed is at the beginning of its growing cycle. Grass is very weed-like in its determination to grow, but different strains of lawn grass have different growing cycles. Another factor is the climate where you live. Some grasses grow best in cool weather while other strains like it hot. In general, grass grows best with moderate temperatures (between 55 and 80 degrees Fahrenheit), full sunlight and lots of water.
Cool Weather Grasses
Cool-weather grasses, such as Kentucky bluegrass, fescue, buffalo grass and ryegrass, are meant for the cooler northern climates and do best when seeded in the spring or fall. Planting in those seasons ensures moderate temperatures and plenty of gentle rainfall. A spring seeding in April or May will give grass a couple of months to establish strong root systems before the heat of summer arrives. Fall seeding in late August and early September works nearly as well, allowing grass to develop a full root system before winter sets in. The soil is warm from the summer, most weeds have completed their life cycle, and people are less likely to be running around outdoors on the new turf.
Warm Weather Grasses
Warm weather grasses, such as bahiagrass, centipede grass and Bermuda grass, are meant for warmer southern climates and do best when seeded in late May and June. These grass types grow best in hot weather, provided they get plenty of water. To keep tender shoots from scorching in the hot sun, spread a light straw mulch to create a sort of shade trellis over your new lawn, or mix the seed with soil before spreading. Be sure to keep the ground moist but not soaking wet.
Seeding and Cultivation
For new lawns, the top 4 inches of soil should be tilled and then leveled with a rake. Then evenly spread a lawn-starting fertilizer with timed-release nutrients over the area. Use a drop spreader to sow your grass seed over the area, according to the rate specified on the seed label. Then go over the seeded area with the backside of a rake to cover the seed. Apply a light straw mulch and sprinkle water to moisten the soil. After germination, water daily until grass reaches about 2 inches tall, making sure the grass gets at least an inch or two of water per week. You never want the soil to dry out completely, nor soak the lawn to the point where you have standing water.
Filling Bare Spots
If you need to fill in bare spots on an established lawn, mix your grass seed with commercial topsoil, one large handful of seed to a 20-pound bag of topsoil, in a wheelbarrow or garden cart. When thoroughly mixed, use a shovel to sprinkle a thin layer of the seed/soil mixture over the bare spots. Water thoroughly with a garden-hose sprinkler and keep moist until the grass sprouts.