Should I Frost Seed?

As temperatures begin to increase following  winter, we are entering a period of warm days and cold nights. These conditions result in our soils going through freeze thaw cycles, which make for a perfect time for frost seeding. Frost seeding involves strategically broadcasting or overseeding legumes into pastures, hayfields, or small grains. It is a potentially cost-effective solution to revitalize a diminishing stand or introduce new legumes. However, success hinges upon assessment of the existing stand, proper timing and soil conditions.

Assessing the stand 

A thick thatch or dense stand of existing plants can pose a challenge, hindering optimal seed-to-soil contact and fostering competition for the seedlings. To mitigate this, it is recommended to closely hay or over-graze in the fall or winter to open the canopy in preparation for frost seeding. Ideally, visible bare spots are a good indicator of a pasture or hay stand where frost seeding is more likely to be successful.

Timing and soil conditions 

Two important factors to consider for the success of frost seeding are timing and soil conditions. Typically, frost seeding falls between mid-February and early March, coinciding with the freeze-thaw cycles. This past week has started to exhibit this cycle with cold nights and warm days, indicating the potential opportunity for implementation. However, checking future forecasts is crucial, as many parts of the state are experiencing warmer temperatures. We need to check the lows and highs for the freeze-thaw interaction. The rhythmic expansion and contraction of soil during freezing and thawing create a honeycombing effect (Figure 1), facilitating seed incorporation into the soil profile and ensuring good seed-to-soil contact. Looking for this honeycombing is a good indicator that the freeze-thaw cycle is occurring and can help determine when to frost seed. 

Additionally, attention is required to avoid soil compaction, which necessitates early morning operations while the soil remains frozen to prevent soil compaction when the soil is wet. Under some conditions, the use of animals can help incorporate the seed, ensuring seed-to-soil contact through their hoof action, but doing this when the field is too wet can lead to the pugging up of the pasture.

Other considerations

Seed selection plays a crucial role in frost seeding success. Red clover and birdsfoot trefoil are great options, as they establish fairly well with frost seeding and provide excellent forage quality. Other legumes, such as white clover and alfalfa, can also be considered depending on the pasture's needs and soil conditions; however, success is more variable with these species. Typically grasses are not good frost seeding options. 

The fate of the seeded stand hinges significantly on spring and soil moisture levels. Adequate moisture is vital for establishing a healthy stand, and soil moisture is necessary for the freeze-thaw cycle to occur effectively. In many parts of Iowa soil moisture or proper temperatures may not be appropriate for an effective freeze thaw cycle for frost seeding. Thus, while the potential benefits of frost seeding are high, timing, soil condition, and moisture play important roles in success. 

Evaluation of your stand, future weather forecast, and soil moisture conditions can help determine whether frost seeding is an appropriate option this spring.