Rye grass is one of the most widely grown grasses in the world. It establishes easily and grows quickly, and is most suited to cooler, temperate climates. It is often called "winter rye grass" because it is used to overseed lawns with warm season grasses that die back in cold weather. Rye grass is also a very nutritional animal feed that is grown in pastures.
Annual Rye Grass
Annual rye grass (Lolium multiflorum), also called Italian rye grass, originated in Europe. According to the University of Wisconsin Cooperative Extension, there are over 1.2 million acres of annual rye grass grown in the United States. It is commonly used for lawns and turf, and it is also used in mixtures for pasture plantings, particularly when establishing a new pasture because it can survive very wet conditions and cold weather where there is good snow cover. In temperate climates, annual rye grass can behave more like a biennial or perennial and continue growing up to five years. It isn't tolerant to extreme temperatures, however. In the southernmost regions of the country, it can be sown in the winter on top of warm season grasses like Bermuda grass, while in northern regions it is more often grown in the summer and fall months.
Perennial Rye Grass
Perennial rye grass (Lolium perenne) is native to Asia, North Africa and Europe. In temperate regions, it grows year round, though it might die back in very hot or cold weather. In lawns, it's often mixed with fescue or bluegrass because their growing cycles are slightly different and the rye grass stays green and strong while other varieties are re-establishing after the cold weather. Perennial rygrass is widely used as forage or pasture grass for livestock because it's digestible, nutritious, and palatable for the animals. Because its roots are shallow and extensive, rye grass can also be used as a cover crop to prevent erosion in fallow fields. The Oregon State University Extension Service warns that perennial ryegrass sold for turf or lawns has a fungal endophyte added to it to increase its insect resistance, which can harm livestock if used for food.
Intermediate Rye Grass
Intermediate rye grass is hybrid rye grass. Rye grass does not self-pollinate well, but annual and perennial varieties cross pollinate very easily amongst themselves and with fescue varieties. There are dozens of cultivars of intermediate rye grass. Some are grown for increased yield while others might have better cold, heat, or drought tolerance. Some varieties are chosen for their color and texture, and some types are more insect and disease resistant.