Perennial ryegrass (Lolium perenne) is a grass that has many uses but probably does not get the credit it should. Kentucky bluegrass is known as the ideal lawn grass, fescues are known for shade and low maintenance, and perennial ryegrass is typically known for speedy germination and not much more. Not that speedy germination is not a good trait to be known for, but perennial ryegrass is much more than a nurse grass.
It is very quick to germinate and is capable of going from scattered seed to mow-able lawn in about 21 days. Perennial ryegrass is considered a nurse grass because it is often included in grass seed blends mainly for its ability to germinate quickly and provide shade and protection to the other grass species like Kentucky bluegrass which can take up to three weeks to get started.
Perennial ryegrass is also a formidable lawn grass on its own. It is a hardy, low-maintenance grass that has elements of insect and disease resistance built in. It has a pleasant, pale green color and happens to be the main species of turf at August National Golf Club (home of the Masters) and Wimbledon Tennis Club. It is great for reclaiming construction areas and can prevent erosion quickly when used on steep banks like on roadways and ditches.
The main issue perennial ryegrass has against it is its growth habit. It forms clumps and cannot spread through stolons or rhizomes like other grass species. As a result, it can sometimes appear patchy and bare spots need to be regularly re-seeded as they will not fill in on their own. Perennial ryegrass can also struggle to thrive in shady areas preferring open, sunny locations.
It has been known to have a coarse texture and dull mowers have a tendency to shred the leaf blade rather than shear it, but newer improved cultivars have largely gotten rid of the problem. Perennial ryegrass does better in the transition zone and the less extreme areas of the north. The severe winters of the upper part of the northern states and Canada can kill perennial ryegrass.
Perennial ryegrass is ideally suited for seed blends, especially when rounding out the numerous qualities of Kentucky bluegrass and fescues. With some well-selected cultivars of all three types of grass, a thoughtful seed blend will thrive in a lawn and all the various micro-climates that can be within a yard. It makes the most sense to use a seed blend than to side with any one particular grass species, especially if there are shade trees coexisting with sunny areas and other extreme differences in the yard.
Perennial ryegrass is also popular in southern climates as a winter grass. In areas where warm-season species go dormant in the winter, perennial ryegrass is often over-seeded to provide color for the winter season. When the heat of the summer returns, so does the warm-season turf.
Things to Consider
It is important not to confuse perennial ryegrass (which returns year after year) to annual ryegrass, Lolium multiflorum, (which dies out after one season). Annual ryegrass is sometimes used as a winter green-up, but it is also used in cheap, inferior seed blends because it is cheaper than quality perennial ryegrass seed. It can be useful in a pinch or where it may not be wanted the following season, or even because it co-exists with centipede grass better than perennial rye, but it is also used to deceive unaware customers.
Overseeding With Ryegrass. Clemson University
Moore, Kenneth J. Forages - Volume 2 - The Science of Grassland Agriculture. Wiley-Blackwell, 2020