If you're looking to rejuvenate pasture or hay fields, applying seed to the ground and allowing the freezing and thawing of soil in February and early March will provide seed-to-soil contact, allowing germination of seed.
There is a little more risk of the seed not germinating than a traditional seeding, but the cost and time is a lot less. The secret is to have exposed soil. Pasture and hay fields that have thin stands and exposed soil are good candidates for frost seeding.
Medium red clover is the cheapest seed and works well. Other clovers will also work.
Some steps to improve germination include mixing fertilizer with the seed, as the fertilizer will scratch the seed coat and improve germination. If the ground can withstand heavy equipment, seed can be mixed with fertilizer at a bulk plant.
Keep in mind that when you apply this mixture with a “spinning seeder,” fertilizer will travel twice as far as the seed, so you will want to cut the application rate in half and overlap by half when applying the fertilizer and seed.
Some have had success letting livestock tramp in the seed with their hooves.
A light grazing of fields when grass starts growing will keep down grass competition as the clover starts. Don’t worry about hooves tramping and killing the new seedlings as the increased sunlight will provide added growth and vigor of the remaining plants to become established in the stand.
A heavy, round seed like clover has a better chance of making soil contact than a light, flatter seed. Garry Lacefield, Extension forage specialist from University of Kentucky, says clovers, seeded in the right conditions, will germinate most years.
Grasses are more “hit or miss,” germinating about half of the time.
With alfalfa, the odds are even less. Frost-seeding alfalfa into an alfalfa stand rarely works, as existing alfalfa is toxic to new plants.
If an alfalfa field is starting to thin out, an option to extend the life of the stand would be to frost-seed red clover.
Another reason to plant clover, especially red clover, is the high seedling vigor. It's tolerant of a wide range of soil pH and fertility conditions and is more drought tolerant than white clover.
The advantage of frost-seeding a legume like red clover is that legumes “fix” nitrogen typically in excess of their own needs, providing added fertility to other plants, and improving stands.
Once legumes become established in a stand of grass and compose 25% to 30% of the stand, there is no need to provide additional nitrogen, which reduces fertility costs.
Other legumes that can be frost-seeded are birdsfoot trefoil and annual lespedza. Birdsfoot trefoil is a persistent perennial once established, but is slow to do so. Some have had success mixing it with red clover.
Annual lespedza, especially in southern portions of the Midwest, is an option. It's nonbloating, drought tolerant and will tolerate poor soils. Expect growth in July and August and do not graze after early September to allow the plants to produce seed for future crops.
A final note on legumes. When seeding a legume that has not been grown in a field for years, it's important to include the proper inoculum with the seed to ensure that the bacteria responsible for fixing the nitrogen will be present.
If you choose to frost seed grass, which will do best? Studies by Dan Undersander, forage specialist from University of Wisconsin, indicate that perennial ryegrass will do best, followed by orchardgrass, then timothy.
Other studies note that annual ryegrass will work good compared to other grasses. Several have had better success with grasses by no-tilling into the sod, and the more you can suppress the existing stand (grazing, herbicides, etc.), the better the odds of a successful establishment.
Finally, no matter what you choose to plant, use improved varieties. Numerous studies confirm that those varieties will last several years longer in most conditions. Recent forage trials at Ohio State University show there are several red clover varieties that have high yields and stand percentages of 60% or greater after 4 years.
These are more expensive varieties than some of the common, shorter-lived varieties, but it may be worth it to some growers.
If you are seeding on much of a slope, avoid frost seeding where there is snow cover because the seed may move during the melt. As a result of snow conditions in many areas, this may leave us a small opportunity to seed.
One of the most common reasons of failure is waiting too long to seed. If you get into late March and do not have damp soils and frosts and an early growth of grass, success will be greatly reduced.
Frost seeding is a low-cost seeding method that can allow farmers to renovate pastures and hay fields by increasing the legume content and moving some improved genetics into the mix. The end result can be a low-cost, more-productive, higher-yielding stand that requires less nitrogen fertilizer.