March is the month across much of Michigan to improve pastures by frost-seeding legumes like clovers or some grasses into them. Frost-seedings are most successful when the seed is broadcast approximately 45 days before grass growth begins in your area.

Frost-seeding is the practice of broadcasting seeds of improved varieties of red clover, white clover, birdsfoot trefoil or some grasses in late winter across grasslands. The freezing and thawing action of the soil surface over the following weeks helps to incorporate the seed into the top soil layer, thus providing good soil-to-seed contact and stimulating early germination.

Both research and farmer experience has shown frost-seeding with legumes to be a simple, inexpensive and environmentally-friendly method of pasture improvement. It can also be used on hayfields if spring grass competition is controlled. Field demonstrations conducted with red and white clover by Michigan State University Extension show that an investment in seed, inoculant and starter fertilizer at $35 to $45 per acre can increase the yield of unimproved pastures by 0.8 to 1.5 tons per acre dry hay equivalent for a $12 to $15 per acre annual cost, assuming three-year clover longevity. Frost-seeding is so much more economical than applying nitrogen fertilizer that even if one year’s frost-seeding fails because of weather conditions, you can afford to do it again next year and it will still be cheaper than applying nitrogen every year.

However, frost-seeding is not foolproof. It must be done properly to have a high degree of success. Below are guidelines to make frost-seeding successful.

  • Frost-seeding works best on loam or clay-based soils; sandy soils will not work as well because there is not enough soil movement during freeze-thaw cycles on sands. For sandy soils, use a no-till or conventional grain drill to apply the seed into the pasture sod in April.
  • Because it requires freeze-thaw action in the soil, frost-seeding is less effective in areas where snowpack does not melt before night temperatures are consistently above freezing.
  • Graze the pasture short in late fall to weaken the grasses present so they will not be as aggressive next spring, and to expose more soil to provide better soil to seed contact next spring.
  • Soil test the pasture to make sure fertility is adequate, paying special attention to phosphorus as young seedlings need phosphorus for good seedling root growth.
  • Shoot for a 60% grass, 40% legume mix in the final pasture stand as this balance will provide optimum pasture growth and forage quality without raising the risk of animal bloat too high.
  • To attain these mix percentages, frost-seed 8 pounds per acre of red clover or 1-2 pounds per acre of white clover; do not apply both red and white clover in the same year because of the competition they give each other and, combined, they raise the risk of bloat.
  • If the legume choice is birdsfoot trefoil, seed 10-12 pounds per acre as bloat is not an issue with trefoil and it does not establish as easily as the clovers.
  • Use improved varieties of these seeds (the best variety the seed company has) as these varieties seem to be more aggressive and catch better than cheaper bin run varieties, and they usually last longer in the stand.
  • Frost-seeding is better done on a little snow cover as it is easier to see the spread pattern on top of the snow—usually mid- to late March is good for much of Michigan.
  • Let the pasture grow up to 8-10 inches tall and graze it down tight. Let it grow up to this level again and graze it tight again. Clover tolerates shade from the competing grass for a while, but if the grass gets too thick and tall, which most grass stands do in spring, the young clover seedlings need some chance to receive sunlight to catch up. If frost-seeding on a hayfield, take first cut as early as possible to reduce shading on the new clover seedlings.
  • Continuous grazing is not good for new clover seedlings. After grazing, the seedlings need a chance to grow, so rotating the animals to another pasture is advised.
  • Do not fertilize the frost-seeded pasture with nitrogen fertilizer the first spring of seeding as it will create too much grass competition for the clover seedlings. Usually by mid-summer the clovers are visible and can handle the grass competition, so small amounts of nitrogen could be applied, if needed, at that time.
  • Red clovers will last two to three years normally in a stand. White clovers will persist two to four years. Evaluate pastures in late summer to early fall, if rainfall is adequate, to determine if a frost-seeding of legumes will be needed next spring.
  • Grasses that can be frost-seeded include annual and Italian ryegrass, perennial ryegrass and festulolium. Keep in mind that frost-seeding with grasses has lower success rate than with legumes because lightweight, irregularly shaped grass seeds do not work into soil as easily.
  • If weeds are a problem in a pasture, think about soil testing, applying necessary lime or fertilizers, and spraying a labeled herbicide for weeds, if necessary, a year before frost-seeding. Most herbicides that control pasture weeds will also kill clovers that you frost-seeded.

Frost-seeding pastures with improved legume and grass varieties is a very economical way of improving pasture yield and quality. When done properly and followed by adequate summer rains, it can be successful.

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