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FEATURED ARTICLE: Considerations When Overseeding Warm-Season Grasses

September 1st, 2007

by Dr. Charles H. Peacock
NC State University

Despite the miserably extreme summer temperatures this year, after Labor Day there will be a change in the climate and thoughts will turn to fall overseeding especially for golf course fairways. This practice has been routine for almost 50 years in the southern US, but it always seems to have controversy. If overseeding is an option that is chosen for whatever reason, there are some considerations that should be made.

Bermudagrass usually stops growing and turns brown after the first hard frost. It remains dormant until temperatures consistently reach 60 F next spring. Overseeding provides color, uniform surface conditions, and wear tolerance. While the overseeding process is usually conducted in mid to late fall, preparing bermudagrass for overseeding is a year-long process. Bermudagrass must be healthy to withstand the harsh cultural practices and turf competition associated with overseeding.

Seeding Date

Successful overseeding can be done two to three weeks before the expected first frost date or when the soil temperature declines to 75 F. Overseeding in the Raleigh area is usually done between September 15 and October 1. Western and northwestern areas of the piedmont may be seeded one to two weeks earlier, whereas the south central and southeastern areas of North Carolina may be seeded one to two weeks later.

Overseeding Preparations

Close mowing just before overseeding is essential. Hybrid bermudagrasses should be thinned using a dethatching mower, and clippings and thatch should be removed with a sweeper. It may be possible to skip the dethatching process with common bermudagrass. Any coring should have been completed several weeks in advance and the cores dispersed by dragging. This prevents spotty germination.

Postseeding Care

Irrigation two to three times daily until the seedlings begin to emerge is critical. If water restrictions prohibit this, then whether to try overseeding at all should be questioned. Irrigate just enough to moisten the surface while preventing lateral movement of the seed. As seedlings emerge, reduce irrigation frequency to daily, and eventually irrigate only as needed. Begin mowing the grass at a height of 1/2 to 3/4 inch. Weekly mowing is often sufficient in late fall and winter, but mowing twice a week is the spring norm.

Fertilization

Do not fertilize with nitrogen during the initial time of overseeding because this may encourage the bermudagrass to compete with the young plants. Adequate levels of phosphorus and potassium should be maintained for good plant rooting. A soil test in the summer should have been done to determine if additional starter fertilizer is required. If not, applying these at the time of fertilization can help in the establishment process. Using a 0-10-20 at 1.0 pound of potassium per 1000 square feet (44 pounds per acre) can be beneficial. Begin to use nitrogen fertilizer shortly after shoot emergence and continue until cold weather halts the overseeding growth. This normally requires the application of 1/4 to 1/2 pound of nitrogen per thousand square feet every two or three weeks, or 1 pound of controlled-release nitrogen per thousand square feet every four to six weeks.

Entry Filed under: Turfgrass Care & Maintenance