Now is the time to be thinking about improving pasture stands by either the frost seeding method in February and early March or interseeding later in the spring months. Below are guidelines and considerations when it comes to frost seeding or interseeding.
Frost seeding involves spreading forage seed on existing pastures during the late winter or very early spring while the ground is still frozen. Freeze-thaw cycles then provide shallow coverage of the seed, which help shield the seeds from early spring rains. Frost seeding is the easiest method to add new forage legumes 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.
When it comes to frost seeding, don’t frost seed on top of a snow cover. The goal of frost seeding is to get seed on bare soil. If snow accumulates after you’ve frost seeded on bare ground, that is perfectly fine.
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 and Outreach publication Improving Pasture by Frost Seeding.
Interseeding offers an opportunity for improving pasture productivity too. Interseeding involves using a no-till drill to add additional forage species into an existing pasture stand. 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. While a number of drills are available for use in sod-seeding efforts, drills vary in their effectiveness based on ability to penetrate sod, provide uniform seed depth and metering, and the ability to cover the furrow. Equipment limitations for sod-seeding implements sometimes are overcome by operator experience and home shop modifications.
Clovers, alfalfa, and birdsfoot trefoil are legumes that have been successfully interseeded. Legumes interseeded into grass sod will help increase pasture yield, improve forage quality, and eliminate or minimize the need for nitrogen fertilizer. Perennial forage grasses can also be successfully established by interseeding. Thin, low-producing, grass sod might best be improved by interseeding a grass 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.
Interseeding success depends a lot on paying attention to details, timeliness, careful management of sod competition, 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 and Outreach publication Interseeding and No-Till Pasture Renovation for more suggested seeding rates and guidelines.
For more information, please contact your local Iowa State University Extension and Outreach field agronomist.