Grass seed grown in North America is generally divided into three types; cool season grass seed, warm season grass seed, and transitional zone grass seed.

Cool Season Grass Seed

Cool season grasses are those species which are adapted to cool summer growing conditions found north of the Mason-Dixon line which roughly divides the United States north and south. The primary cool season species are Kentucky bluegrass seed, perennial ryegrass seed, creeping red fescue seed, chewings fescue seed, hard fescue seed, and bentgrass seed. Cool season grass seed species will not persist under hot summer growing conditions and can be used in the southern US only at high elevations or for winter overseeding of dormant warm season grasses. Cool season grasses will survive snow cover that is fatal to warm season grasses.

Warm Season Grass Seed

Warm season grasses are those species which are adapted to the hot growing conditions found in the southern and southwestern US. The primary warm season species are bermudagrass, zoysiagrass, St. Augustinegrass, Bahiagrass, and centipedegrass. Zoysiagrass and certain bermudagrass varieties can be planted north of the Mason-Dixon line, but they are temperature sensitive and will lose their green color earlier in the fall and green up later in the spring than cool season grasses.

Transition Zone Grass Seed

Tall fescue is a species of grass seed that is best adapted to growing conditions in the transition zone, the broad area running east to west across the US that separates the warm season and cool season growing areas. Tall fescue seed is adapted from the costal areas of New York and New England south to northern Georgia and west to Dallas, St. Louis, and the coastal regions of California. Tall fescue seed is adapted to both full sun and partial shade growing conditions.

Grass Seed Growth Habit

Grass seed species vary in their ability to spread and thicken up over time. Some grasses spread by underground lateral shoots known as rhizomes. Most notable of these is Kentucky bluegrass, which is renowned for its ability to fill in a dinner plate sized dead spot in one growing season. Creeping red fescue spreads by weak lateral shoots which are not nearly as vigorous as bluegrass.

Bermudagrass and creeping bentgrass spread by above ground lateral shoots known as stolons. Both these varieties will eventually take over a lawn if they are adapted to the growing conditions.

Other grass seed species do not spread but will thicken up by putting out tillers, or additional leaf blades attached to the crown of the plant. These varieties include perennial ryegrass, chewings fescue, hard fescue and most varieties of tall fescue.