By Jerry Lindquist
Improving pastures with late winter frost seedings of certain legumes and grasses can be successful. If the planning and preparation is not started until seeding time however the odds of success may be diminished.
Frost seeding of clovers, birdsfoot trefoils, and some grasses such as annual and perennial ryegrass can be a very economical way to improve pasture forage growth and nutritional quality. Frost seeding is usually performed in late winter typically 40 to 50 days before grass growth begins in the spring. Frost seeding works best on clay and loam soils that experience soil movement with the freezing and thawing action that takes place that time of year. Part of the popularity of frost seeding is its ease of implementation and low cost. Producers have to simply buy the seed, broadcast the seed and watch it grow. There is no spraying, tillage, stone picking, nor loss of grazing for a summer that comes with re-seeding a new pasture. And in many cases the end result can be almost as good as a new seeding.
The common practice is to add a red or white clover seeding to a pasture when the legume percentage in the pasture is less than 40 percent. The existing grass pasture is not tilled or sprayed, just the clover seed is broadcast over top with the hope that the clover seedlings will compete and grow with the grass in the summer. Even thin stands of grass can be very competitive in the spring of the year. These existing grasses can out-compete the new seedlings for moisture, especially during a dry period in the spring, and the frost seeding may fail.
To give the frost seeded plants a better chance in the spring, over-grazing the grass stand in the fall is advised. When frost seeds are planned, it is the one time that Michigan State University Extension forage educators will advise you to weaken, or hurt the pasture stand in the fall before seeding.
Over-grazing does two things to help the success of the frost seeding. First it reduces the root food reserves of the pasture stand that will cause the grasses to be less aggressive in the spring. Secondly, by taking the grasses right down to two inches of stubble in late fall it removes the thatch layer on the soil surface, exposing more soil, which will lead to better soil-to-seed contact in the spring. Erosion is a slight risk as a result of this practice but the live roots and stubble remain in place preventing the risk of serious erosion. The set back of the stand is only temporary in the spring and the grasses will recover as the frost seeded plants start filling in by June. The benefit of letting the grazing animal be the plant retardant versus tillage and/or herbicide is quickly realized as pasture grazing does not skip a beat in the spring. The additional stand diversity that the new plants provide will benefit the grazing herd, beneficial insects and soil microorganisms in the pasture environment as well.
Source:msu.edu