Frost seeding is an economical way to establish cover crops in standing wheat or barley, or to supplement a thin forage stand.

Right now is the time to perform this practice as the soil is going through freeze-thaw cycles. This causes a “honeycombing” of the soil surface that helps improve seed-to-soil contact. Frost seeding works well on loamy and clay soils that hold water, but it is not suited for use in sandy or shaley soils that dry out quickly.

Here are four tips:

1. Do it early. The best time to perform frost seeding is early in the morning when the soil is frozen and a thaw is expected during the day. This reduces the chance for soil compaction while providing the desired soil heaving that improves seed-to-soil contact.

2. Choose small seeds. The best species for frost seeding generally are small-seeded, germinate quickly and grow well in cool conditions. Red, white and sweet clover are the most successful species, while birdsfoot trefoil can also be used for pasture renovation despite slower germination and early growth.

And although yellow sweet clover can cause animal health problems because of coumarin content (a blood thinner), it is not likely to cause livestock health issues if it is only a percentage in a pasture.

When seeding legumes, be sure to inoculate them with the appropriate rhizobium so the symbiosis will take place to fix nitrogen. In pastures, some nonfluffy grass species such as annual or perennial ryegrass may also be frost seeded.

Do not mix grass and legume seed for broadcast application as the legume seeds will throw farther than the grass seeds because of their greater density, which leads to nonuniform seed distribution.

3. Know seeding rate. Make every attempt to guarantee uniform coverage by knowing the width of spread and spacing between passes.

Recommended species and seeding rates are in the table below. Seeding rates into small grains are higher because no repeat application is possible, while with pasture renovation, frost seeding complements an already established stand and can be repeated next year if not successful.

Heavier seeding rates for pasture renovation would be used in thinner stands. It is common to mix clovers for pasture renovation. Red and ladino white clover make a good combination, where you use twice the seeding rate of red clover as white clover — for example, 2 pounds per acre of red clover, plus 1 pound per acre of white clover, up to 6 pounds per acre red, plus 3 pounds per acre white clover.

4. Use animals to help. Frost seeding will likely be most successful in pastures with bare spots or those that are overgrazed. Besides relying on the freeze-thaw action at seeding, you can also use grazing animals to tramp in the seed shortly after broadcasting. This practice may be especially helpful for improving seed-to-soil contact if a thick thatch layer that would compromise frost-seeding success is present. 

However, don't turn out animals in wet conditions as this can cause soil compaction. If you miss the best “window” for frost seeding, clover seed will remain viable in the soil, and much of it will likely grow when the conditions are right. 

If you notice your stand is not adequate in summer, you can selectively no-till legumes or grasses in late summer to fill in thin spots to resolve any lingering issues.

Duiker is a professor of soil management and applied soil physics at Penn State; Larson is a Penn State Extension field and forage crops educator; Hartman is a Penn State Extension educator for livestock.

Source: Penn State Cooperative Extension, which is solely responsible for the information provided and is wholly owned by the source. Informa Business Media and all its subsidiaries are not responsible for any of the content contained in this information asset.