Frost Seeding Clover Into Pasture Without a Drill

A thin pasture in February and no drill in the shed is a common combination on small acreage. Frost seeding uses the freeze and thaw of late winter to work broadcast clover seed into the ground, and Penn State Extension describes the result as a honeycombing of the soil surface that improves seed to soil contact [1].

What Honeycombing Does to Broadcast Seed

Water in the top half inch of soil freezes overnight and thaws by afternoon, so the surface lifts, cracks, and settles again through the same cycle. Seed broadcast onto that pitted surface drops into the openings and gets covered as the ground settles back down.

Nothing else has to move it, which is the reason the practice works with nothing but a spreader and no tillage at all. The practice does depend on ground that holds water.

Frost seeding works well on loamy and clay soils, and it is not suited to sandy or shaley soils that dry out quickly [1]. Germination then waits on temperature rather than on the calendar, because seed sown in late winter sits in place until temperatures reach 45 F and above [3].

When Should You Broadcast?

The window opens while nights still freeze and days still thaw. Penn State Extension puts that at February to March, when the soil is going through freeze and thaw cycles [1], and in the upper Midwest most frost seeding happens during March [2].

Colder zones typically run later and milder ones run earlier, so read the ground rather than the date on the calendar. Time of day then matters about as much as the month does.

Broadcast early in the morning while the soil is still frozen and a thaw is expected later in the day, which also reduces the chance of soil compaction [1]. Penn State Extension notes that delaying until midmorning, when the soil surface has gone slippery, results in poor stand establishment [7].

Seeding on top of snow is possible when the snow is shallow, though a rapid melt may carry both water and seed off the field in runoff [2]. Shallow snow is the practical limit here, and a forecast warm spell is the reason to wait a day.

Which Clovers Work, and at What Rate

Small, dense, quick germinating seed does best on a frozen surface. Extension broadcast rates for renovating an existing pasture run as follows:

• Red clover, 4 to 8 pounds per acre, and the quickest of them to establish [1]
• White or ladino clover, 2 to 3 pounds per acre, low growing under grass [1]
• Alsike clover, 2 to 4 pounds per acre when it is seeded alone [2]
• Birdsfoot trefoil, 4 to 6 pounds per acre, slow out of the ground [1]
• Annual or perennial ryegrass, 4 to 6 pounds per acre [1], and only for a single season of forage [2]

Red clover and ladino clover make the common pair, using twice the seeding rate of red as white, from 2 pounds red plus 1 pound white up to 6 pounds red plus 3 pounds white [1].

Birdsfoot trefoil behaves differently, because it germinates slowly and grows slowly early on, and University of Minnesota agronomists add that its low seedling vigor may leave it establishing poorly [1] [3].

Ryegrass is the opposite case, often quick to establish and short lived, and ryegrasses do not overwinter well in the Midwest [2].

How to Prepare the Ground and Set the Spreader

Broadcast seed cannot reach the soil through a mat of dead grass, so graze or clip the pasture closely in fall or winter to open the stand and expose the soil [2]. Grazing down to two inches in the fall also slows the grass coming back in spring [2].

A thick thatch layer works against frost seeding, and turning livestock out shortly after broadcasting can tramp the seed in, though not on wet ground where hooves compact the soil [1]. Spreader work after that is mostly a question of swath width.

On a spinner type seeder, determine the effective seeding width for each seed type or mix, because the spread pattern varies between species [2].

A hand crank chest spreader throws light clover seed a short distance and suits a few acres at a walk, while an ATV mounted or a three point hitch seeder covers more ground and holds a steadier rate [2].

Do not mix grass and legume seed in one pass, since the denser legume seed throws farther than the grass seed and leaves the pattern uneven [1]. Halve the rate instead and cross the field twice at right angles.

What Goes Wrong

Four failures account for most thin results: seeding too late, herbicide carryover, skipped inoculant, and spring competition. The first of them is the easiest to see and the easiest to forgive.

Seeding after the last freeze and thaw leaves the seed lying on top of the ground. That seed is not necessarily lost, because clover seed left in the soil after the window closes stays viable and much of it grows when conditions turn right [1].

Residual pasture herbicides are the quieter failure. Picloram can leave a soil residual of up to 2 years, which University of Minnesota Extension flags for anyone planning to interseed legumes into a pasture [5].

Products containing clopyralid and picloram usually carry a crop rotation restriction of up to 18 months for sensitive broadleaf crops, and aminopyralid has begun to replace both while posing the same risk to broadleaf crops [6]. Clover is a broadleaf, so find out what was sprayed and when before ordering any seed.

Clover also needs the right bacteria in the ground. Inoculate with Rhizobium trifolii, the inoculant group B rhizobium for true clovers, meaning the bacterium that forms the root nodules where clover fixes its own nitrogen [4].

Every package of inoculum carries an expiration date, and past that date the bacteria may not be alive [4]. Store the inoculum in a refrigerator without freezing it, and plant within 24 hours of inoculating or else inoculate the seed a second time [4].

Competition from the established sod is the last of the four. New seedlings sit at a competitive disadvantage for light and moisture next to the established grasses already in the sod [3].

Short interval rotational grazing down to a 4 inch height, once the grass canopy reaches 10 inches, reduces that competition and helps the new seedlings get established [3]. Graze the frost seeded ground on that schedule and the sod stops shading the seedlings out.

What Should You Expect by June?

A full stand in the first season is not the normal result. University of Minnesota agronomists report observed seedling survival rates from 0 to 60 percent with frost seeding, and even where seedlings do establish, appreciable new forage growth takes 60 days [3].

Count plants rather than judging the field by its color. Expected established plants at the seeded alone rates run 2 to 5 per square foot for red clover, 2 to 3 for alsike clover, and 1 to 2 for ladino [2].

If the June count comes up short, the pasture can be frost seeded again next winter, or the thin spots can be no till seeded in late summer with single species pasture seed [1]. Either way the count in June is the number to write down and compare against next year.

If the pasture is thin and a drill is not on the place, Nature’s Seed carries clover and pasture mixes sized for small acreage, with a seeding rate chart on every product page. Order early enough in the winter to have the bag sitting in the shed before the ground starts to honeycomb.

Sources

[1] Penn State Extension. Frost Seeding for Cover Crop or Forage Establishment. https://extension.psu.edu/frost-seeding-for-cover-crop-or-forage-establishment

[2] University of Minnesota Extension. Frost seeding forages into established horse pastures. https://extension.umn.edu/horse-pastures-and-facilities/frost-seeding-forages

[3] University of Minnesota Extension. It’s time for frost seeding: Using legumes to meet nitrogen needs. https://blog-crop-news.extension.umn.edu/2022/03/its-time-for-frost-seeding-using.html

[4] Penn State Extension. Inoculation of Forage and Grain Legumes. https://extension.psu.edu/inoculation-of-forage-and-grain-legumes

[5] University of Minnesota Extension. Weed management for pasture and fence line systems. https://extension.umn.edu/agriculture/crop-production/weed-management/weed-management-for-pasture-and-fence-line-systems

[6] University of Minnesota Extension. Managing herbicides in ditch forages. https://extension.umn.edu/agriculture/animals-and-livestock/horse/managing-herbicides-in-ditch-forages

[7] Penn State Extension. White Clover. https://extension.psu.edu/white-clover