Frost seeding can be an inexpensive way to establish legumes in existing grass pastures. The process, says Iowa State University Agronomist Steve Barnhart, involves broadcasting legume or grass seed on existing pastures in late winter or very early spring when the ground is still frozen. Freezing, thawing and early spring rains provide the only seed coverage.

Dr. Barnhart suggests the following steps for successful frost seeding:

Select a suitable site. Chances of success are greater on thin grass stands than on thick, vigorous stands because there is less competition for legume seedlings. Clovers and trefoil are better suited than alfalfa on soils that need lime and to soil with inferior drainage.

Control weeds. If possible, plan a year ahead and spray weeds with 2,4-D. Weeds reduce stand establishment and can be controlled only by clipping once legumes are established.

Soil test and apply needed lime and fertilizer. Adequate plant nutrients aid establishment and increase yields. If possible, apply needed lime one year ahead of seeding. Nitrogen should not be used the season before or the year of frost seeding because it stimulates grasses and weeds, making them too competitive. Phosphorus and potassium, however, are needed by legumes.

Graze closely the fall before seeding. This reduces grass competition and aids establishment. Although it is not considered necessary, disturbing the soil lightly with a disk in the fall before seeding may help legume establishment.

Broadcast seed in late February or March. Seeding should be done when the ground is still frozen. Avoid seeding on heavy snow since a fast melt may wash off seeds. Probability of success decreases with the onset of spring due to higher surface soil temperatures and lower moisture.

Manage grazing after seeding. Control of grass and weed competition during the first two or three months of the growing season is critical for the establishment of adequate legume stands. Use moderate periodic grazing after the grass starts growing, but avoid close grazing. Some mowing may be necessary to help control grass and weeds. After the seeding year, maintain fertility and manage grazing to encourage a productive and long-lived forage stand.
For more information, refer to the Iowa Beef Center Web site at www.ibc.iastate.edu/