Chris Torres, Editor, American Agriculturalist
(Previously published online with American Agriculturalist: March 16, 2021)
Clover 
species are your best bet, as is seeding in more loamy, clay soils.
While nights are still chilly, the days are getting warmer, making it the perfect time to do some frost seeding.
Frost seeding is an economical way to establish cover crops in winter in standing wheat or barley, or to supplement a thin forage stand. And even though it’s not as foolproof as drilling, it’s a reasonably successful practice.
Penn State Cooperative Extension has seven tips to ensure frost seeding success:
#1.
Do it in loamy, clay soils. Frost seeding works well on loamy and clay soils that hold water, but it is not suited for use on sandy or shale soils that dry out quickly.
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.
Clovers work best. 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.
Yellow sweet clover can cause animal health problems because of coumarin content — a blood thinner — but it is not likely to cause livestock health issues if it’s 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.
#3.
Don’t mix grasses and legumes. If you’re broadcast seeding, the legume seeds will throw farther than the grass seeds because of their greater density, which leads to nonuniform seed distribution.
#4.
Make sure coverage is uniform. The best way to do this is by knowing the width of spread and spacing between passes. Here are some recommended species and seeding rates:
Seeding rates into small grains are higher because no repeat application is possible. 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 are 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 red plus 1 pound per acre white clover, up to 6 pounds per acre red plus 3 pounds per acre white clover.
Frost seeding is more successful in pastures with bare spots or those that are overgrazed.
#5.
Animals can help. 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 is 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 that could cause soil compaction.
#6.
Opportunities past frost seeding. 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.
#7.
What to use. Nancy Glazier, a small farms and livestock educator with Cornell Cooperative Extension, says broadcasting is best for frost seeding.
“I would not suggest using a drill,” Glazier says. “The goal of frost seeding is getting on the pasture or small grain field before the ground is ready for a drill and preventing ruts. Broadcasting the seed on ground in the freeze-thaw cycle works the seed down into the soil. A cyclone spreader works well. If a drill is used, one would need to wait until conditions are drier. It might need to be a no-till drill to get through living plant material.”