Published August, 2010

Overseeding horse pastures is a pasture management practice that helps ensure good ground cover, quality grazing, and an aesthetically pleasing pasture in the coming 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. This can be done over the entire pasture or it can be limited to trouble areas. The best time to overseed is in the fall, when weed competition is low and ideal growing conditions exist for cool-season grasses.

Weed control is an important step in overseeding. While herbicides are an effective way to control weeds, spraying might also hinder young seedlings and result in a failed establishment. Close mowing or grazing is usually best to help seedlings establish.

Proper seeding method improves the chance of a successful overseeding. The goal is to place the seed 1/4 - 1/2 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. Land owners also can harrow before and after seeding; however, this method is much less accurate and effective. Use a cultipacker or roller after harrowing to help improve the seed-to-soil contact. Frost seeding (spreading forage seed on existing pastures during the late winter or very early spring while the ground is still frozen) is another option. However, the success of this method greatly depends on environmental conditions and, therefore, is not usually recommended.

Allow time for seedlings to establish. Returning horses to an overseeded pasture too soon can wipe out any seedlings by grazing or trampling. Ideally, a pasture should have one year of rest after overseeding before heavy grazing resumes; however, seedlings can usually tolerate a few sessions of light grazing. Harvesting the pasture once for hay after the grass has reached maturity, before returning the pasture to full grazing, is also recommended. If it is not possible for animals to be removed from the pasture for a full year, consider using temporary fencing and overseeding half of a pasture one year, then the other half the next.

The following recommendations increase the chances of a successful overseeding:

• Apply any needed lime and fertilizer amendments. An up-to-date soil test will indicate the nutrients needed for both established and growing plants. For more information, contact your local county extension agent or consult the UK publication "Lime and Fertilizer Recommendations," AGR-1 (under Publications).
• Use high-quality seed of an improved variety. Use a variety that has proven to be a top performer under Kentucky conditions. The University of Kentucky forage testing program tests the survival of cool season grasses under grazing by horses and reports these findings in Forage Variety Trials. High-quality seed has high rates of germination and is free of contamination from weed seed. Remember, quality seed will produce a pasture that lasts for years; "cheap seed" will only lead to headaches.
• Plant enough seed. Seeding rates are determined by the grass mixture to be planted. See Table 1 for the recommended seeding rates for common forage plants.
• Use the best seeding method available. No-till drill seeding is recommended most for overseeding.
• Control competition. Close mowing or grazing prior to overseeding in the fall reduces weed competition.
• Allow immature seedlings to become established. In addition to limiting grazing of an overseeded pasture, also limit herbicide applications at critical times. Typically, seeding six weeks after spraying and waiting an additional six to eight weeks before spraying again is recommended. Always follow herbicide labels.

Other considerations when overseeding:

• Pastures grazed by pregnant mares should not be planted with endophyte-infected tall fescue. Check to make sure that you are planting endophyte-free 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 (greater than 25%) it will outcompete other grasses, which will result 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 endophyte-free perennial ryegrass should be seeded in broodmare pastures.
• Purchase seed well in advance of overseeding. High quality seed is in high demand in the fall and might not be available at that time.
• Store seed in a cool, dry area to maintain germination levels. Refrigerators are excellent storage sites if room is available. Always store in rodent-proof containers.

Ray Smith, PhD, forage extension specialist in the University of Kentucky College of Agriculture, provided this information. Assistance was provided by Krista Cotton, BS in animal science, Kentucky Equine Management Internship graduate, and pasture evaluation associate.