Lawn Grass: When to Seed and Which Grass to Grow

Cool-season and warm-season grasses

Lawn grasses fall into two groups that grow at opposite times of year, and the group decides when you plant.

Cool-season grasses include tall fescue, Kentucky bluegrass, perennial ryegrass and the fine fescues. University of Delaware notes they grow fastest in spring and fall, with best growth when daily average temperatures are around 68°F, and summer is their stress period. They stay green most of the year and are the lawns of the North, the Pacific Northwest and the higher parts of the transition zone. They are grown from seed or sod.

Warm-season grasses include Bermudagrass, zoysiagrass, centipedegrass, bahiagrass and St. Augustinegrass. They grow fastest in summer, best at 85°F and above (University of Delaware), and turn brown and dormant in cold weather. They are the lawns of the South. Some are seeded and others planted from sod, sprigs or plugs; each grass guide says which.

When to seed a cool-season lawn

Late summer to early fall is the best time. Illinois Extension explains why: the soil is still warm for fast germination, fewer annual weeds compete, and the young grass has fall, winter and spring to establish before summer heat. Its windows for Illinois are early August to early September in the north, mid-August to mid-September in the center, and September in the south. The dates on the grass seed guide count from your average first fall frost to give the same window for your ZIP code.

April is the second choice. Seeding from late spring through midsummer often fails, because heat slows or stops cool-season seedlings before they have roots to survive it.

When to plant a warm-season lawn

Warm-season grasses need warm soil. NC State recommends seeding Bermudagrass, bahiagrass, zoysiagrass and centipedegrass in late spring to early summer, once the soil stays at 65-70°F, and Illinois advises sowing them before summer starts. That gives them the full summer to spread before they go dormant in fall.

The transition zone

Across the middle of the country, between the cool-season North and the warm-season South, neither group is ideal. University of Delaware, which lies in the northern half of this transition zone, describes winters there as too cold for warm-season grasses to stay green and summers as hard on cool-season grasses. It recommends tall fescue for cool-season lawns and zoysiagrass for warm-season lawns in that region. Do not mix the two types in one lawn (Illinois).

Seeding rates and care

Illinois Extension’s seeding rates per 1,000 square feet are 1-3 pounds for a Kentucky bluegrass blend, 3-4 pounds for an 80:20 bluegrass-perennial ryegrass mix, 3-5 pounds for a 50:50 bluegrass-fine fescue mix and 6-9 pounds for tall fescue. Sowing more than that produces weak, spindly seedlings and invites disease. Rake the seed lightly into the surface, keep it moist until it is established, and consider a light straw mulch, about one bale per 1,000 square feet, to hold moisture and soil in place.

Where to start

Choose the grass type for your region first; each grass guide covers where it is adapted, its shade and traffic tolerance, and whether it is seeded or sodded. Then plant in that grass’s season using the dates for your ZIP code.