Frost seeding is a low cost option to renovate a pasture or hay field. It involves broadcasting seed on to the soil surface and letting natural freeze/thaw cycles work to increase seed to soil contact. Fields roughed up by livestock grazing and/or are overgrazed are candidates for frost seeding. In some cases, a light tillage pass can open up the sod canopy enough to allow broadcast seed to reach the soil surface. Thin alfalfa stands can be renovated by frost seeding red clover into the stand.
Timing is important, and every winter is different, but generally, mid-February through March is a good period for frost seeding. This winter we seem to be in a pattern where we have cold temperatures and snow followed by a few days of above average temperatures and melted snow cover. Some of those transition zone temperature ranges combined with little or no snow cover provide opportunities for frost seeding.
Successful frost seeding is dependent upon several factors:
- Seed to soil contact. You must be able to see areas of bare soil looking down into the sod. Frost seedings fail where a thick sod base that covers the soil. Bunch types of sod, composed of orchardgrass and/or tall fescue, work better to frost seed into than sod-forming grasses such as bluegrass.
- Freeze/thaw action. This happens when we get nighttime temperatures in the 20’s and daytime temperatures in the 40’s, preferably for at least several days after broadcasting the seed.
- Forage species. Frost seeding works best with heavier seed that has a better chance of getting down to the soil surface. Legumes such as red and white clover work well and have good seedling vigor. Birdsfoot trefoil is also a good candidate for frost seeding but it is a slower establishing species and it may need 2 to 3 years after seeding before it makes much of a contribution to the pasture mix. Grasses do not establish as well with frost seeding, but there has been some limited success with frost seeded perennial ryegrass and orchardgrass.
- Soil pH and fertility are important. A soil pH of 6.5 is desirable for legume plants. Critical or base level soil test recommendations for phosphorus and potassium are 25 ppm or higher (Bray P1 extractant) for phosphorus and 120 ppm for soil potassium.
- Management after frost seeding. The new legume seedlings need sunlight to develop. This means that the grass plants in the sod mix can’t be allow to shade out the new seedlings. It will be necessary to do either a quick “flash” grazing pass to take off the top of the grass plants and leave a 4 to 4.5 inch residue or a mowing that leaves the same residual height.