Published August, 2011

Overseeding horse pastures that contain cool season grasses can help improve pasture production and forage quality and ensure a good ground cover the following year without major pasture renovations.

Overseeding consists of planting seed in a field with existing grass cover to fill in bare patches and thicken the stand. Property owners can overseed the entire pasture or just the trouble areas. The best time for overseeding is the fall when weed competition is low and ideal growing conditions exist for cool-season grasses. The ideal time for overseeding in Kentucky is Sept. 1-15. Seeding dates might be earlier in northern regions and later in areas south of Kentucky. In areas with long cold winters, overseeding should occur in early spring. Note: In this article we will not discuss overseeding bermudagrass pastures with annual ryegrass.

Controlling competition from weeds is an important first step in overseeding. While herbicides are an effective way to control weeds, spraying can also hinder young grass seedlings, resulting in a failed establishment. Check your herbicide label for the recommended waiting period before seeding. More important than spraying weeds is mowing or grazing pastures close before seeding. This not only knocks back weeds, but reduces the chances that the existing pasture “shades out” the young seedlings that are just getting started.

Proper seeding method is also a key factor in overseeding success. The goal of any method is to place the seed ¼- to ½-inch into the soil and cover it to achieve good seed-to-soil contact. Use a no-till drill for the best chance of success. Make sure the drill is set correctly to keep seed at the correct depth. Harrowing before and after broadcast seeding is another method; however, it is much less effective than drilling. Using a cultipacker or roller after the harrow method can help improve seed to soil contact. Finally, frost seeding is an option for overseeding clovers. Frost seeding involves broadcasting seed onto the ground during mid to late February and relying on the freeze and thaw cycle to work the seed into the soil. Frost seeding works well with red and white clover, but success is limited with grasses and alfalfa.

Allowing time for seedlings to establish is another critical step in overseeding. Returning horses to an overseeded pasture too soon can wipe out any seedlings by grazing or trampling. Ideally, a pasture should have six to eight months of rest after overseeding before normal grazing resumes; however, seedlings can generally tolerate a few sessions of light grazing. Another option is to take a cutting of hay in the spring before returning to full grazing. If it is not possible for animals to be removed from the pasture for six to eight months, consider using temporary fencing and overseeding half of a pasture one year and the other half the next.

The following recommendations will increase your chances of success when overseeding pastures:

1. Apply lime and fertilizer amendments as needed. An up-to-date soil test will indicate both established and growing plants' nutrient needs. For more information, contact your local County Extension Agent or consult the UK publication Soil Sampling and Nutrient Management in Horse Pastures. A low rate of nitrogen at seeding (30-40 lbs/acre) will improve the chances of successful establishment.
2. Use high-quality seed of an improved variety. High-quality seed has high rates of germination and is free of contamination. Use a variety that has proven to be a top performer under local conditions. The University of Kentucky forage testing program tests the survival of cool-season grasses and legumes under grazing and reports these findings in Forage Variety Trials. Many other states also have Forage Variety Trial data.
3. Plant enough seed. Seeding rates are determined by the grass mixture to be planted. See Table 1 (below) for the recommended seeding rates for common forage plants.
4. Use the best seeding method available. We recommend using a no-till drill for overseeding.
5. Control competition. Close mowing or grazing prior to overseeding will reduce existing grass and weed competition.
6. Allow immature seedlings to become established. In addition to limiting grazing of an overseeded pasture, also limit herbicide applications at critical times. Typically, seeding should not occur until six to eight weeks after spraying. After you have overseeded you should also wait approximately two months before spraying a newly overseeded stand (the new grasses should be 4 to 5 inches tall). With clovers the waiting period for seeding after spraying can be six or more months with some herbicides, so always follow herbicide labels.

Other considerations when overseeding:

• Do not plant endophyte-infected tall fescue in pastures grazed by pregnant mares. Check to make sure that you are planting endophyte-free or novel endophyte tall fescue in broodmare pastures.
• Perennial ryegrass is a short-lived, cool-season grass that has exceptionally high seedling vigor and is often used to thicken troublesome areas. If perennial ryegrass is seeded at high rates (above 20%) it will outcompete other grasses, resulting in bare spots as perennial ryegrass dies out in two to three years. Perennial ryegrass can be infected with an endophyte similar to that of tall fescue; therefore, only use endophyte-free perennial ryegrass.
• Purchase seed well in advance of overseeding. High-quality seed is in high demand in the fall and might not be available if you try to purchase right before your seeding date.
• Store seed in a cool, dry area to maintain germination levels. Always store in a rodent-proof container.

Kelly Prince, an MS candidate, Krista Lea, MS, and Ray Smith, PhD, professor and forage extension specialist, all within the University of Kentucky Department of Plant and Soil Sciences, provided this information.