Perennial ryegrass (Lolium perenne) and annual ryegrass (Lolium multiflorum) are generally used to overseed dormant warm-season lawns in South Carolina. They provide a green cover during the winter when the warm-season grasses go dormant and turn brown after frost. Also, they can be used as a winter cover to help prevent erosion on new lawns where the permanent grass has not been established. However, overseeding may retard the warm-season grass unless managed correctly in the spring, because the ryegrass competes for moisture, sunlight and nutrients.
Ryegrass adapts well to either sun or shade. Although cheaper, annual ryegrass is a second choice to perennial ryegrass, since perennial ryegrass has more desirable turf characteristics. Annual ryegrass dies out in late spring after being planted in the fall. Perennial ryegrass usually lives somewhat longer than annual ryegrass, especially in the shade. It can survive for years in some areas of the lawn where it can become a nuisance. It has better disease resistance than annual ryegrass. It is not recommended as a permanent lawn, however, because of its susceptibility to diseases in hot weather. Ryegrasses should only be used in South Carolina for overseeding in the fall.
It is important to prepare the turfgrass for winter. As temperatures begin to drop in the fall, water demands of turfgrass decrease. Take care not to overwater, as disease problems may increase. Remove any excess thatch so the seed can make good contact with the soil. A heavily thatched lawn tends to result in irregular patches of overseeded grass. Dethatching by verticutting or aerifying will assist overseeding heavily thatched lawns. If core aeration is necessary, overseed thirty days after aeration to allow the holes time to heal and provide an even turf in the winter. Dethatching by verticutting should be performed just prior to overseeding. Mow the lawn closely, catching all clippings or raking afterwards.
Overseeding should be done when the days are warm enough for the seed to grow and the nights are cool enough to reduce the incidence of disease. Thirty days before the first frost, when daytime highs are near 70 °F and nighttime lows are usually above 50 °F, is generally a good time to overseed. This usually corresponds to mid-September in the Upstate and late September in the Midlands and Coastal regions.
When overseeding into an established lawn, apply 5 pounds of ryegrass per 1000 square feet. This should give you a green cover without causing transition problems in the spring due to a thick stand of ryegrass. If the area you are overseeding is barren, and you are overseeding to reduce soil erosion, then apply 10 pounds of ryegrass seed per 1,000 square feet. This will produce a thicker ryegrass cover that can be removed before renovation in the spring.
Sow half the seed in one direction and the other half in a direction perpendicular to the first. This method will help establish a uniform stand of turf. Use fungicide-treated seed to reduce the chances of disease. If you are overseeding into an established turf, after seeding brush the turf with a stiff broom to ensure the seed falls through the thatch and makes contact with the soil.
Water the lawn lightly two or three times daily until the seeds germinate. The amount of watering, or syringing, during establishment will be determined by the soil type and evaporative potential of the atmosphere. Syringing is a very light spray of water over an area to moisten the seed. Clay soils that do not drain well may not need as much syringing as overseeding on sandy soils during dry periods.
Do not overwater, as this will wash seed away and encourage disease development. When the lawn is established, and has been mowed several times, water only as necessary to prevent ryegrass wilt.
An established winter lawn requires the same maintenance as a permanent lawn. Mow when the grass is tall enough to cut, about 1 to 2 inches. Mow to 1 to 1½ inches thereafter whenever the grass reaches 2 to 2½ inches. Make sure the mower blade is sharp to prevent ripping of the ryegrass. If ryegrass is properly fertilized, weekly mowing may be necessary.
After the second mowing, apply one-half pound of nitrogen per 1000 square feet using a complete fertilizer, such as 16-4-8, 10-10-10 or others. Apply another one-half pound of nitrogen mid-winter if needed to maintain ryegrass color and growth. Pythium blight disease can be a problem on overwatered, overfertilized ryegrass, especially during warm, humid weather, so it is important to monitor the nitrogen applications and to not over- fertilize or over-water.
Reestablishment of the Permanent Lawn
Ryegrass normally dies out in late spring, but if cool weather prevails, it can become persistent. To discourage the ryegrass, fertilize the ryegrass no later than January. Allow the lawn to remain on the dry side if possible. This will stress the ryegrass and allow transition back to your warm-season turfgrass. However, do not allow the permanent grass to suffer from lack of water at this time.
Mow the ryegrass as close as possible in spring by lowering the mowing height each week. This will weaken the winter grass and allow the permanent grass to rejuvenate. Be sure to not scalpe the permanent lawn as this could also cause a delay in transition (i.e., green up in the spring). When the permanent grass resumes growth, begin regular maintenance, especially fertilization.
The following is one last item to mention on overseeding warm-season turfgrasses. Once a lawn has been overseeded, it will need to be overseeded the following years because ryegrass seed that did not germinate the previous year may germinate and grow into big clumps and look weedy. If a lawn that has been previously overseeded with ryegrass will be left fallow, then a preemergent herbicide application will need to be made to prevent both winter weeds and grasses from germinating.