By Ray Smith

Overseeding of pastures is an excellent management tool that improves pasture production, forage quality, and ensures a good ground cover the following year without major pasture renovations. Overseeding consists of planting seed in a field with existing grass cover in order to fill in bare patches and thicken the stand. It can be done over the entire pasture or limited to trouble areas. The best time for overseeding is the fall when weed competition is low and ideal growing conditions exist for cool-season grasses.

Controlling competition from weeds is an important step in overseeding. While herbicides are an effective way of controlling weeds, spraying may also hinder young seedlings, resulting in a failed establishment. Carefully check the label for the recommended waiting period before seeding. In general, weeds are less aggressive in the fall, making it the best time to overseed. Usually, close mowing or grazing can help seedlings establish.

Many overseeding applications fail to establish due to grazing the pasture too soon after seeding and grazing too heavy the first 6-8 months.

Proper seeding method is also an important factor in overseeding success. The goal of any seeding method is to place the seed ¼ to ½ inch into the soil and cover it to achieve good seed to soil contact. Using a no-till drill is recommended to provide the best chance of success. Harrowing before and after broadcast seeding is another seeding method; however, it is much less accurate and effective than a no-till drill. 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 is 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 livestock 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 heavy grazing resumes; however, a few sessions of light grazing can generally be tolerated by seedlings. Another option is to take a spring hay cutting 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, then the other half the next.

The following recommendations will increase the chances of a successful overseeding application:

• Apply any needed lime and fertilizer amendments – An up-to-date soil test will indicate the needs of many nutrients needed for both established and growing plants. For more information, contact your local County Extension Agent or consult the UK publication AGR-1: Lime and Fertilizer Recommendations. A low rate of nitrogen at seeding (30 to 40 lbs/acre) will improve the chances of successful establishment.
• 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 and legumes under grazing 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 – Using a no-till drill is recommended for overseeding, as discussed previously.
• Control competition – Close mowing or grazing prior to overseeding will reduce existing grass and 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 grasses should not happen until six to eight weeks after spraying and wait an additional six to eight weeks before spraying a newly overseeded stand. With clovers the waiting period for seeding after spraying can be six or more months with some herbicides. Always follow herbicide labels.
• Allow immature seedlings to become established – In addition to limiting grazing of an overseeded pasture, also limit herbicide applications at critical times. Typically, seeding grasses should not happen until six to eight weeks after spraying and wait an additional six to eight weeks before spraying a newly overseeded stand. With clovers the waiting period for seeding after spraying can be six or more months with some herbicides. Always follow herbicide labels.
• Other considerations when overseeding – Perennial ryegrass is a short-lived, cool-season grass that has exceptionally high seedling vigor and is often used to thicken up troublesome areas. If perennial ryegrass is seeded at high rates (above 20%) 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.

Purchase seed well in advance of overseeding. High quality seed is in high demand in the fall and may not be available at that time.

Store seed in a cool, dry area to maintain germination levels. Always store in a container that is rodent proof.

Table 1. Common seeding rates and optimum seeding dates for pasture plant species

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