Cool-season grasses include tall fescue, perennial ryegrass and Kentucky bluegrass. These varieties germinate easily and are most often established by seed rather than installing sod. Seeds of cool-season grasses can be planted in late summer to early fall. Varieties other than bluegrass can also be planted in late winter to early spring, though fall is generally considered the better time period. Cool-season grasses planted in spring have a higher risk of injury from summer heat.
A few cool-season grasses, most notably tall fescue and hybrid bluegrass, can also be established as sod, which is more expensive but has the benefit of creating the appearance of an "instant" lawn. The best time to lay sod for these grass varieties is January through June or September through December.
Warm-season grasses are generally established as sod, but seeding works for varieties like common Bermuda grass, centepedegrass and Chinese lawngrass. If you choose one of these varieties, the best time to plant seeds is late spring into early summer.
Late spring and early summer are also the best time to lay sod for warm-season grasses, but timing is not as essential for sod as it is for seed. Sod can be established at any time during the growing season as long as the soil is neither frozen nor extremely dry. Warm-season varieties commonly established through sodding include zoysia, St. Augustine grass and hybrid Bermuda grass.