It is not generally recommended to overseed home lawns, but if it is performed, it should only be on a bermudagrass lawn. The extra irrigation, fertilization, and shading effects of the overseeding will severely retard or damage centipedegrass, zoysiagrass, and St. Augustinegrass in the spring and early summer and cause undesirable competition on the permanent turfgrass.
Perennial ryegrass (Lolium perenne) and annual ryegrass (Lolium multiflorum) may be used to overseed dormant bermudagrass lawns in South Carolina. They provide a green cover during the winter when this warm-season grass goes dormant and turns brown after frost. Alternatively, they can be used as a winter cover to help prevent erosion on new lawn areas where the permanent grass has not yet been planted. Keep in mind that overseeding may even retard the bermudagrass, unless it is managed correctly in the spring, because the ryegrass competes for moisture, sunlight, and nutrients.
Ryegrasses adapt well to either sun or shade. Although cheaper, annual ryegrass is a second choice to perennial ryegrass for lawn quality, since perennial ryegrass has more desirable turf characteristics and better disease resistance than annual ryegrass. In addition, annual ryegrass is lighter in color than perennial ryegrass, coarser in texture, and dies out more quickly in spring after a planted in fall. However, the problem is that perennial ryegrass cultivars usually live much longer into early summer than annual ryegrass, especially in the shade. It can even survive for years in some areas of the lawn, where it can become a nuisance. Perennial ryegrass is also not recommended as a permanent lawn because of its susceptibility to diseases during hot weather. In summary, ryegrasses only should be used in South Carolina for overseeding in the fall on bermudagrass lawns using good turfgrass management techniques, or for use as erosion control during the fall and winter, when permanent warm season turfgrass will be installed the next spring. For more information for proper bermudagrass care, please see HGIC 1216, Bermudagrass Yearly Maintenance Program.
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. For more information on aeration, please see HGIC 1200, Aerating Lawns. Dethatching by verticutting should be performed just prior to overseeding. Mow the lawn closely, catching all clippings or raking afterwards. For more information on dethatching, please see HGIC 2360, Controlling Thatch in Lawns.
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 early October in the Upstate and late October in the Midlands and Coastal regions.
When overseeding into an established lawn, apply 5 pounds of ryegrass per 1000 square feet. This should give the lawn a green cover without causing transition problems in the spring due to a thick stand of ryegrass. If the area is barren, and overseeding is used 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 permanent lawn establishment 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 overseeding an established lawn, brush the turf with a stiff broom to ensure that the seeds fall through the foliage and make contact with the soil.
Water the lawn lightly two or three times daily until the seeds germinate. The amount of watering during establishment will be determined by the soil type and evaporative potential of the atmosphere. During dry periods, poorly drained clay soils may not need as much irrigation as sandy soils.
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. Thereafter, mow to 1- to 1½-inches tall whenever the grass reaches a height of 2 to 2½ inches. Make sure the mower blade is sharp to prevent ripping the ryegrass blades. If the 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 fertilizer, such as 16-4-8 or 15-0-15 (this would be 3 pounds of fertilizer per 1000 square feet of lawn). Apply another one-half pound of nitrogen during mid-winter, if needed to maintain ryegrass color and growth. Pythium blight disease can be a problem on over-watered, over-fertilized ryegrass, especially during warm, humid weather; therefore, 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, fertilizer applications should be made no later than mid- to late January. If possible, allow the lawn to remain on the dry side. This will stress the ryegrass and allow the transition back to warm-season turfgrass. However, do not allow the permanent grass to suffer from lack of water at this time.
In the spring, mow the ryegrass down to one inch height, which will weaken it and allow the permanent grass to rejuvenate. Be sure to not scalp 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.
One last item should be mentioned about overseeding bermudagrass. Once a lawn has been overseeded, it will need to be overseeded the following years, because the ryegrass seed that did not germinate the previous year may germinate and grow into big clumps and look weedy. If lawn overseeding will be discontinued, then previously overseeded lawns will require a fall application of preemergent herbicide to prevent both winter weeds and any remaining ryegrass seeds from germinating.
Excerpted from Southern Lawns, Bert McCarty (editor) and the University of Florida Extension publication Florida Lawn Handbook.