February is the time to frost seed existing pastures to add to or improve forage species. But if you prefer interseeding to achieve the same results, you should plan to drill the seeds later in the spring.
"Producers wanting to add to or improve the forage species in their existing pastures should consider using either the frost seeding method in February and early March, or interseeding later in the spring months," says Steve Barnhart, Iowa State University Extension forage agronomist. He offers the following explanation and seeding guidelines.
Frost seeding is the easiest method, and likely less expensive
Frost seeding involves spreading forage seed on existing pastures during the late winter or very early spring while ground is still frozen. Freeze-thaw cycles then provide shallow coverage of the seed, which help shield from early spring rains. Frost seeding is the easiest method to add new forage legumes or grasses to pastures, and is likely the least expensive method, as well.
To increase this method's success, spread seed on the thinnest pasture sod areas first and on areas where bare soil has been exposed due to heavy grazing or disturbance. One common misconception about frost seeding is that spreading the seed on top of snow works best. The goal of frost seeding is to get seed on bare soil. This is more effective and more safely done without snow cover.
Red clover has been the Iowa forage species of choice for frost seeding. Other legumes, such as white clover and birdsfoot trefoil, also can be frost seeded but with less success than red clover. In general, frost seeding does not work as well with grasses. A few well researched steps will improve the success of frost seeding. Those steps, seeding rates and guidelines are available in the ISU Extension bulletin Improving Pasture by Frost seeding .
Interseeding can also be used to boost pasture productivity
Interseeding offers an opportunity for improving pasture productivity, too. It is a little different approach. Interseeding involves using a no-till drill to aid in the incorporation of a legume or a more productive grass into an existing pasture sod. Interseeding is normally done from mid-March through early May, when soil moisture and temperature are more suitable for rapid seedling establishment.
Interseeding can be accomplished with relatively few field operations. Opening of the grass sod, shallow seed placement, and seed coverage are required. A number of drills are available that can be used in sod-seeding efforts.
Some of these drills may have improved features related to sod penetration, depth control, seed metering, or coverage that improves their effectiveness in sod seeding situations. Equipment limitations for sod seeding implements sometimes are overcome by operator experience and home shop modifications.
Legumes interseeded into grass sod should increase pasture yield, improve forage quality, and eliminate or minimize need for nitrogen fertilizer. Clovers, alfalfa, birdsfoot trefoil have been successfully interseeded.
Drills place seed more precisely to improve low-producing sod
The more efficient and more precise seed placement provided by a no-till drill allows many of our more productive perennial forage grasses to also be successfully established by interseeding. Thin, low-producing, grass sod might best be improved by interseeding a grass and legume mixture.
A seeding delay into late spring to improve growing conditions often also leads to a greater competition from the existing grass sod. Close grazing in the fall or spring, ahead of interseeding, will help to reduce sod competition. Contact herbicides are sometimes also used to temporarily further reduce competition from plants present in the stand. Use only labeled herbicides for sod suppression --and follow label instructions.
Success with interseeding requires attention to details, timeliness
Interseeding success depends a lot on paying attention to details, timeliness, careful management of sod completion, controlling seeding depth to no deeper than one-fourth to one-half inch, and a little bit of luck with weather.
Interseeding research has been conducted in many parts of the U.S. and around the world. It shouldn't come as a surprise that the conclusions from these efforts all point to several very important issues that must be met for successful interseedings. See ISU Extension bulletin Interseeding and No-Till Pasture Renovation for more information, suggested seeding rates and guidelines.
Interseeding a pasture is done with a no-till drill in the early spring.