Long proven effective through the natural reseeding of birdsfoot trefoil along with the “volunteer” appearance of red clover and white clover, frost seeding can provide an easy and inexpensive way to renovate a pasture during the winter months. The freezing and thawing of the ground and early spring rains provide coverage for the seed and reduce the need for additional input rendering frost seeding a cost-effective and efficient solution to establishing legumes in an existing pasture.
Frost seeded stands are most successful when the seed is broadcast on either bunchgrass sod (such as orchardgrass), in very thin sods of Kentucky bluegrass, or into smooth bromegrass. Bare and disturbed pasture areas work well due to the lowered competition during establishment.
One of the pivotal determining factors for a successful frost seeding is that competition with seedlings needs to be reduced in contrast to the increased competition seen in vigorous stands of sod-forming bromegrass and bluegrass. Thinner stands allow for increased rain splash coverage from early rains and the freeze-thaw effect that provides coverage for the seed is more pronounced the thinner the original stand is. Abnormally dry springs and early summer weather will hinder rather than help with your frost seeding, and can ultimately cause a frost seeding to fail. When frost seeding fails, carryover for germination later in the season will be limited.
Options for frost seeding include alfalfa, red clover, birdsfoot trefoil, and sweet clover if seeding into established switchgrass and other tall, warm-season perennial grass stands.
Alfalfa seedlings are less vigorous when in competition with pasture grasses than they would be in a more traditional new hay or pasture seeding. If a pure alfalfa or trefoil stand is used for frost seeding, the stand during the year of seeding usually appears thin. By the second and third years, the stand will fill out and improve. When alfalfa is used, it should be frost seeded into soils that are well-drained, near neutral in pH, and adequately fertilized with phosphorus and potassium. In optimum soil and growings conditions, these frost seeded stands may last four years or more of rotational grazing.
Red clovers, alsike clover, and white clovers offer the benefits of increased seedling vigor. When dealing with soils that are poorly drained and use less lime, these clovers are recommended for the greatest chance of success. While clover vigor is helpful when frost seeding, the clovers are also a shorter-lived solution than other types of frost-seeded species. Red and alsike clover stands often persist well for two growing seasons, while Ladino and white clover stands may last three years or more.
Birdsfoot trefoil has provided the greatest success in frost seeding of a single species due to its relatively slow spring growth and low level of competition when compared with alfalfa and red clover. Although birdsfoot trefoil is slower to establish, it is bloat-free, longer-lived, and does well under a wider range of soil conditions than the aforementioned clovers and alfalfa.
To ensure a successful frost seeding, a mixture of trefoil and red clover will provide the best overall situational coverage and give the very best chances of success. The mixture of trefoil and red clover will provide long-term success through the complementary strengths of the two species. While the red clover will establish quickly and produce well for one or two years, it will eventually die out. During this time the red clover is the predominant species, the trefoil stands will be improving, and eventually replace the red clover as the dominant legume in the stand. The longest-term solutions for a single species planting will be birdsfoot trefoil, followed by red clover, and finally, white clover as these legumes will persist in pastures, spreading as volunteer plants in later years by natural reseeding.
Grasses can be frost seeded as well if desired. Perennial species in order of success are timothy, orchardgrass, and tall fescue. Even though annual and perennial ryegrasses contain rapid establishment potential, their summer dormancy and erratic winter hardiness make them less desirable candidates for perennial pasture stands. Genetic improvements could make grasses more suitable alternatives in the future.
Many producers approach frost seeding with the attitude they are attempting to establish the legume or grass species as a new component in a mixed stand. As a result, seeding rates are usually just a fraction of what is used to plant a pure stand of that species in a tilled seedbed. To be successful, seeding rates for frost seeding should be equal to the seeding rate used on a prepared seedbed. The use and cost of additional seed will be partially offset by reduced costs in labor, tillage operations, and seeding equipment. The higher seeding rate in the tables below leads to greater chances of success and improved stand density, while the lower numbers indicate the minimum that should be used when frost seeding.