The type of grass you have growing in your lawn helps you determine how often to mow, how short you can cut the grass, and how much water or fertilizer the lawn needs. If you didn't plant the lawn, you'll have to take a good look at the grass to find out what species is growing there. Kentucky bluegrass and ryegrass are both cool-season grasses, but there are distinguishing characteristics to help you tell them apart. Keep in mind that there might be more than one species of grass in the lawn, because grass seed is often mixed to take advantage of the strengths of different types of grass.
Annual ryegrass (Lolium multiflorum) is typically planted in Southern states to provide green color on the winter lawn. This grass is not planted as part of a permanent turf, but will reseed itself and can come back if it was planted once and allowed to go to seed.
Perennial ryegrass (Lolium perenne) is hardy in U.S. Department of Agriculture plant hardiness zones 3 through 8, and Kentucky bluegrass (Poa pratensis) is hardy in zones 2 through 7. Both ryegrasses and bluegrass grow best in full sun locations that get plenty of water.
Cool-season grasses like ryegrass and bluegrass share a basic structure. Stems, also called shoots, grow up from the roots and leaves grow from the stems. The leaves consist of a sheath that wraps around the shoot, a grass blade and the collar region where the sheath and blade connect. Variations in the appearance of these parts helps identify the species.
- Auricles are short appendages growing from the collar region, which wrap around the lowest part of the leaf blade in certain grasses. Annual ryegrass has long, claw-shaped auricles, and perennial ryegrass has smaller auricles. Kentucky bluegrass does not have auricles.
- If you look at new growth on annual ryegrass, the leaves are rolled in the bud. Perennial ryegrass and Kentucky bluegrass leaves are folded while in the bud.
- The tips of the leaf blades for both ryegrass species have a tapered shape. Kentucky bluegrass has a boat-shaped leaf tip.
- Annual ryegrass has a lime-green color, while the perennial variety is a richer green. Kentucky bluegrass is dark green with some blue tones.
Both annual and perennial ryegrass are bunch-type grasses. They spread by stems called "tillers," or by seeds. These plants grow in a clump, and you'll see them sending out long stems rather than spreading from the roots. If allowed to flower, they form a slender spike-shaped bloom stalk.
Kentucky bluegrass, on the other hand, is a rhizomatous grass. You'll see it spreading from the root rhizomes as well as by tillers to form a thick turf. If allowed to flower, the bloom stalks have a loose, open shape that distinguishes bluegrass from ryegrass.