Window for frost seeding a cover crop fast approaching

Colleen Kottke
Wisconsin State Farmer
While the ground is still frozen, farmers are able to take advantage of the small window and frost seeding a cover or forage crop.

While many farmers are looking forward to the spring planting season later this spring, agronomists like Ted Hoffman urge farmers to consider frost seeding a cover and forage crop in the coming weeks.

Frost seeding really mimics the natural system of the surface placement of seed in late winter or early spring. The process relies on help from Mother Nature by relying on the freeze-thaw cycle and spring rains to establish seed to soil contact as opposed to physically drilling the seed into the soil. Instead, the up and down movement of the freeze and thaw cycle causes tiny fissures or honeycombs in the soil which ultimately draw in the seeds.

Hoffman, who lead the webinar "Frost Seeding Opportunities for Cover Crop Establishment" hosted by Between the Lakes Demonstration Farm Network in conjunction with the Ozaukee County Demonstration Farm Network on March 2, says there are many reasons to consider frost seeding: spreading on frozen ground eliminates compaction, may be faster than drilling a cover crop, frost seeded covers have a jumpstart on drilled covers, and farmers can hire the job out.

Timing is everything

Just with any other seed application process, timing is everything. Hoffman cautions farmers to watch field and snow conditions carefully before proceeding. The optimum window of opportunity for frost seeding is short - late February to early March, when the ground is thawing during the day but temperatures remain below freezing at night.

"The best time for frost seeding is pre-dawn until 8 a.m., that's basically when the soil is going to be the coldest" Hoffman said. 

Spreading seed on top of snow if fine as long as it isn't a heavy packed layer.

"What you're looking for is to have maybe an inch and a half of really light fluffy snow where when you spread the seed it's going to make it at least halfway through that snow down to the soil surface," Hoffman said.

Steve Hoffman, president and managing agronomist at InDepth Agronomy, says farmers would do well to observe what's happening out in the fields as temperatures rise above freezing during the day.

"As we start to see some snowmelt, what's happening to that water that's coming off that snow? Is it actually running off the field, or is it a slow degradation where it's slowly soaking in," he said. "Watch the weather forecast. If you've had a significant amount of snow and temperatures are expected to be 50 degrees in two days, I would try to avoid those kind of situations where you're going to have some runoff occurring."

Although temperatures are expected to rise in the coming week, Hoffman said that even if the snow has melted, if there are nights when the temperatures dip down into the 20s, farmers should still be able to plant seeds.

Frost seeding

There three methods commonly used in frost seeding: spinner spreader, airflow fertilizer spreader, air seeder and a drill.

Those considering the use of a spinner spreader should consider applying at a half rate, going over the field twice in the opposite direction for even establishment. 

"If you try to apply a full rate in just one direction," Ted Hoffman said," it's pretty likely you will end up with some streaks, whereas an airflow spreader provide a nice, even spread pattern."

Hoffman says an air seeder is ideal as producers can dial in the application rates in order to put on light rates of small seeded cover crops. 

"If you don't have access to any of those spreaders, a drill can work too. You need to have the drive wheel engaged with the DD openers not penetrating the ground," he said. "A word of caution, don't skimp on seeding rates (with any type of spreader). Because we are spreading seed on the soil surface, we will probably get a bit lower germination."

Compatible crops for frost seeding include small seeded grasses, winter cereals, Italian rye grass, orchard grass, festulolium, some legumes such as clovers, birdsfoot trefoil and maybe vetch.

"There hasn't been a lot of work done using alternative cover crop species in a frost seeded scenario. That's one of those things we don't know unless we try," Hoffman said. "Don't be afraid to take a small field or take a strip in a field and try out a cover crop even if you're going to end up burning it off in the spring just to see if it's something that's going to work for frost seeding."

Soybeans emerge among the rye grass stubble.

Frost seeding systems for NE Wisconsin

Hoffman says that frost seeding a cover crop can help control weeds and build carbon for soil health. Adding additional seeding to winter injured alfalfa can also help provide additional forage as well.

Groups like Between the Lakes Demonstration Farm Network, NRCS, Great Lakes Restoration and Ozaukee County Demonstration Farm Network have experimented with frost seeding using different types of seed species - noting the results of success or need for improvement.

Some of the systems that have produced good results include: frost seeding rye into corn stubble in front of soybeans; red clover frost seeded into winter wheat; additional forages frost seeded into winter injured alfalfa; and clover frost seeded before corn.

Hoffman says benefits of the frost seeded crops were many. Rye planted in the corn stubble provided some shading for the soybean plants which allowed the soybeans to canopy quicker. The rye also had an allelopathic effect, which inhibited weed growth or helped to stop the germination of weeds. "Which basically seemed to act as a soil residual for us," Hoffman said.

Frost seeding clover into winter wheat provided a boost in forage production following the harvest of the wheat.

"The whole point of this system is that as soon as the wheat comes off, the clover is fixing nitrogen which then will be available for next year's crop," he said. "This really sets it up well for no till corn the next year."

A good way to increase tonnage on an aging stand of alfalfa is to seed additional forage into the existing crop.

"You can also get some emergency forage by doing this," Hoffman said. "In year where we have winter kill or winter injury, this is going to fill in those low areas with the most damage. The grass and clover will really thrive there and it will help reduce soil erosion."

Although it takes time, new plants clover plants begin to emerge in an established stand of hay.

Steve Hoffman warns farmers that it takes time for frost seeded clovers and grasses to really contribute after planting.

"The first, second and even third crop they're skeptical because they're not seeing a lot," Steve Hoffman said. "But by the fourth cutting, I've heard from several customers that the growth was very significant."

Ted Hoffman says the frost seeded crops also provide a boost of nutrition for the livestock that will eventually consume them. The results from a cutting of clovers and grasses were promising with protein, calories and sugar levels exceeding the values of straight alfalfa.

"And the people that we have out harvesting forages like this are making milk out of it," he said. "I have no worries that these frost seeded crops are going to negatively affect the forage value of your alfalfa."

Frost seeding red clover in front of corn still needs a bit of fine tuning Hoffman says.

"The success really depends on the winter annual pressures. Did you have a lot of dandelions or mare's tail in that field? If so, and you did nothing last fall, you're not likely to have great success with frost seeding clover in front of corn," he said. "If you have those winter annuals, maybe you need to consider doing a fall burn leaving some residual that's friendly to the clover next year."


Hoffman says it's important to consider what soil residual herbicides are still there from the previous crop of corn and soybeans.

"Did you use some soil residuals that have a very long half life or aren't friendly to cover crops? If you don't know that, ask your agronomist to read the label," he suggested.

If using a fertilizer spreader, Hoffman suggests using 100 pounds of carrier as a minimum. "The best spread pattern is achieved with 150 pounds of carrier total product to get that even pattern," he said. "Be sure to calibrate your drill or air seeders, especially for small seeded covers. Just setting it for alfalfa and hoping for the best is a recipe for failure."