When is it too late to frost seed?
In northern Missouri late February to early March is generally the best time to frost seed legumes into pastures. Weather, such as deep snow followed by prolonged cold, may interfere. Here is some advice from the Missouri Grazing Manual, courtesy of the MU Forage Systems Research Center, to help in planning around weather to get legumes seeded into established pastures.
The limiting factor regarding which species can be successfully frost seeded is tolerance to cold weather while in the seedling stage. Red and white clover can be frost seeded with very consistent success due to high seedling vigor and frost tolerance in the seedling stage. Although quite susceptible to freezing in the cotyledon stage, these clover species become very hardy after the emergence of the first trifoliate leaf. Alfalfa and birdsfoot trefoil are less tolerant of cold temperatures in the seedling stage and are thus more susceptible to stand failure when frost seeded.
Most successful frost seeding will occur if seed is broadcast late February through early March in north Missouri. The seed must come in contact with the soil for frost seeding to be effective. For this reason competition from established forages and weeds must be controlled.
Spring grazing will allow some of the seed to be trampled into the soil, if soil moisture is not excessive. If chemical suppression of the sod is to be used, it should be done the previous fall. Waiting until spring when green growth has begun to apply herbicides makes frost seeding much less effective.
Pasture burning to retard cool-season grass growth in the spring generally occurs too late as legume seedlings should already be up and growing by the optimum fire date. However, broadcast seeding immediately into the ash bed following a spring burn has been reported work with adequate rainfall after seeding.
Sod disturbance combined with frost seeding works quite well as the roughened soil surface is more conducive to good seed-soil contact due to freezing-thawing activity. If pastures are to be harrowed for manure dispersion, broadcast seeding at the same time often gives better results than simply frost seeding, particularly with birdsfoot trefoil and alfalfa. If a harrow is used, seeding is usually delayed until later in the spring after the risk of late frost is lessened. The success rate is generally high if slight sod disturbance is combined with broadcast seeding and harrowing in spring.
For more information on frost seeding legumes into pasture visit extension.missouri.edu, click agriculture, crops, forages and select the publication for the legume you are interested in seeding.
Source: Max Glover, Agronomy Specialist