• Ryegrasses (Lolium spp.) is a genus comprising of nine species of grass used for turf, hay, and grazing applications. Not to be confused with the food grain rye, ryegrasses thrive in cool, moist weather, and are closely related to the large grass genus of fescues. Numerous named varieties of annual and perennial types of ryegrass are marketed throughout the United States.
  
  

Annual Ryegrass

• Annual ryegrass (Lolium multiflorum) has traditionally been presumed to have very little cold tolerance and is therefore is assumed to die off over the winter in much of the United States. The University of Wisconsin Extension advises that annual ryegrass is primarily used as a high-quality single-season forage crop for dairy cattle, taking advantage of its quick, lush summer growing habit. The University of Illinois Extension, however, advises that annual ryegrass has become a popular winter cover crop for corn and soybean farmers throughout the midwestern United States. A 2008 Illinois Extension report found marked differences in cold hardiness between the 19 named varietals of annual ryegrass tested over the course of 3 years' field study, with varieties such as King and Bounty demonstrating near-perennial overwintering tendencies. Annual ryegrass is also used in turf and lawn applications; the University of Texas Extension advises that annual ryegrass reseeds naturally in the south, emerging in the fall as cooler temperatures and autumn rains descend.
  
  

Perennial Ryegrass

• Perennnial ryegrass (Lolium perenne L.) is best adapted to cool, moist growing conditions. There are several varietal names of perennial ryegrass on the market. According to the Wisconsin Cooperative Extension, the primary use of perennial ryegrass is grazing for cattle and sheep. However Richard Dubie, Turfgrass Specialist for the Texas Cooperative Extension, notes that newer varieties of perennial ryegrass bred for turf applications are increasingly popular for overseeding southern ballfields, golf courses, and residential and commercial lawns in the winter, when local heat-tolerant summer-grown grasses go dormant.
  
  

Short Rotation Ryegrass

• According to the University of Wisconsin Extension, short-rotation ryegrass (Lolium hybridum) is a cross-breed of annual and perennial ryegrass varieties, currently marketed under the varietal name "Bison." The Wisconsin Extension advises that short-rotation ryegrass is less cold-hardy but more productive than perennial ryegrass; they recommend its use for livestock grazing and hay in the north-central United States.