There's more than one kind of ryegrass; in fact, three different types of grasses contain "rye" in their names. It's easy to be fooled, so it's best to distinguish between the three types as they have different uses.
Understanding the Differences Between the Three Kinds of Rye
When the use of common names causes confusion, it's helpful to turn to the scientific names of the plants for some clarity. Here are the botanical names for the three grasses in question (along with their most commonly-used common names):
- Lolium multiflorum (annual ryegrass)
- Lolium perenne (perennial ryegrass)
- Secale cereale (winter rye)
When speaking informally, however, people sometimes refer to all three as " winter rye." That's all the more reason to insist on the use of the botanical name when a positive ID is needed.
Another noteworthy difference is that winter rye (Secale cereale), unlike the other two, is a grain. Thus another common name for it: "cereal rye." So think of this one in the way that you would think of wheat or a similar grain, not a lawn grass. Another difference is that winter rye is a more robust plant than either annual ryegrass or perennial ryegrass.
Despite these differences, they all share one thing (besides having similar names): They're cool-season grasses.
Uses for Annual Ryegrass
The best-known use for annual ryegrass is in overseeding lawns, specifically, in overseeding lawns that are composed of warm-season grasses in the South. When the warm-season grass goes dormant in these lawns during the months of cooler temperatures, overseeding with a cool-season counterpart (annual ryegrass) provides a way to enjoy a green expanse for a longer duration. By the time this annual grass dies out, the weather will have become suitable again for the warm-season grass to take over.
Annual ryegrass is also used in emergencies to cover bare ground temporarily until the landscaper has a chance to get a perennial grass established. "Nurse crop" is the name for this role. An example would be to fight erosion in a pinch. The seed is cheap so people sometimes turn to this grass when they can't afford a better option; annual ryegrass also germinates quickly, making it ideal for such stop-gap measures.
A simple experiment can prove its rapid germination. Sow seeds of creeping red fescue, Kentucky bluegrass, and annual ryegrass in small containers on August 21, for example. By August 25, the annual ryegrass will have already germinated. The next one (the fescue) will not germinate until August 28; the Kentucky bluegrass will germinate shortly thereafter. Even after germination, the three patches will be markedly different, with the annual ryegrass being by far the thickest and tallest of the three.
This vigor is a double-edged sword. Its tolerance to a variety of conditions and its ability to reseed quickly mean that annual ryegrass is potentially an invasive plant. If you decide to use it as a nurse crop and don't want it to spread, try to keep it from going to seed by mowing faithfully until it runs through its natural life cycle and dies out.
Uses for Perennial Ryegrass
Perennial ryegrass is used extensively in lawns. It is commonly found as part of a grass seed mix. Such mixes are composed on the principle that a weak point of one type of grass (lack of shade tolerance, for example) in the mix can be offset by a strong point of another. In the case of perennial ryegrass, a strong point is that it holds up well to foot traffic.
Like annual ryegrass, another strength of perennial ryegrass is that its seed germinates rapidly, making it a good nurse crop. It's often made part of grass seed mixes because it's so effective at affording shade to a grass-like Kentucky bluegrass until the latter can get established. A weak point, though, its clumping growth habit, which some people don't like because it makes a lawn look patchy. Perennial ryegrass is different in this respect from many lawn grasses, which possess the ability to spread via stolons or rhizomes, allowing them to fill in better.
Uses for Winter Rye
Winter rye is the best known of these three grasses to the general public. That's because it is enjoyed as an edible not only by livestock but also by people. Its grain is used for the flour that gives us rye bread. Others will be more familiar with the use of the grain in producing whiskey. Here we'll concern ourselves with the use of winter rye as a "cover crop," in which capacity it offers several benefits.
One of those benefits is weed control, which winter rye excels at due to that horticultural superpower known as "allelopathy" (the ability to inhibit the germination of the seeds of competing plants). The potential drawback, as mentioned by the University of Vermont extension, is that "allelopathic compounds may suppress germination of small-seeded vegetable crops as well if they are planted shortly after the incorporation of cereal rye residue."
Nonetheless, winter rye managed properly, is very effective as a cover crop, boasting good cold-hardiness, a deep root system (to prevent erosion and loosen the soil), and good drought tolerance compared to other cereals.
Many rural homesteads sow winter rye seed in fall. The exact time for sowing will depend on your region (ask your local extension), but the idea is to get your cover crop established before winter settles in. All you have to do thereafter for a while is wait for winter to end and let the cover crop do its job of "covering for you" until spring returns.
In spring, you mow the winter rye, then use a garden tiller to turn it under. Some gardeners, rather than rototilling every last bit of this biomass underground, save some to use on top of the ground as a mulch, in which case you're essentially growing your own mulch.
Either way, the real question becomes when to mow winter rye. If you don't want your cover crop to outstay its welcome, the timing for mowing is critical, because you face the challenge of something termed "grow-back."
Its annual life cycle doesn't preclude winter rye's sometimes growing back. A cold-hardy annual such as winter rye will keep growing until it achieves its goal in life, which is to bear flowers so that it can produce seeds. So if you mow too soon, it may make a comeback and put on more growth in an attempt once again to bloom (which you don't want). On the other hand, if you wait too long to mow, the plants will, indeed, go to seed and live on through a second generation. You don't want that, either.
A Goldilocks solution is called for (mowing not too early, not too late). While you can often get away with mowing at a height of 12 to 18 inches (this is what the University of Vermont recommends) without experiencing grow-back, a surer way is to keep an eye out for flowering and mow at that time.