I have been getting questions about seeding forages, both frost seeding and drilling, and this year’s weather pattern needs to be considered when making a seeding decision. Generally March is a good time in our area to consider frost seeding. Frost seeding works better some years than others. Successful frost seeding is dependent upon several factors:
- The broadcast seed can actually get down to the soil surface. For this to happen you have to be able to see bare soil when you look down upon your sod base. This will not work if there is a thick sod base that covers the soil. Bunch types of sod, composed of orchardgrass and/or tall fescue, work better to frost seed into than sod-forming grasses such as bluegrass. To prepare for frost seeding the recommendation is to “rough up” or “open up” the sod by grazing down tight or mowing very low in the late fall or in the early spring. If livestock are used to do a grazing pass the hoof action can also help to open up the sod. Light tillage may also work.
- Freeze/thaw action. This happens when we get night-time temperatures in the 20s and day-time temperatures in the 40s, preferably for at least several days after broadcasting the seed. These type of days have been very limited to date. If you read any of the fact sheets about frost seeding you typically will see the phrase “broadcast seed on to frozen soil.” We do not have frozen soil this year, thanks to the unseasonably warm temperatures we have experienced in February. This may be another strike against frost seeding success this year.
- Forage species. Frost seeding works best with heavier seed that has a better chance of getting down to the soil surface. Legumes such as red and white clover work well and have good seedling vigor. Birdsfoot trefoil is also a good candidate for frost seeding but it is a slower establishing species and it may need two to three years after seeding before it makes much of a contribution to the pasture mix. Grasses do not establish as well with frost seeding, but there has been some limited success with perennial ryegrass and orchardgrass when frost seeded. I believe that for the dollars spent for seed, drilling grasses is the preferred method of establishment. Broadcast legume and grass seed separately because the difference in seed weight between the legume and grass seed results in the grass seed not being thrown as far as the legume seed.
- Soil pH and fertility are conducive to good seedling establishment and growth. Soil pH should be at a minimum above 6.0 and preferably at 6.5 if legumes are being sown. Phosphorus is an important element for new seedling growth and soil phosphorus level should be at 25 ppm or higher (Bray P1 extractant). Soil potassium should be in the 120 ppm range.
- Management after frost seeding. The new legume seedlings need sunlight to develop. This means that the grass plants in the sod mix can’t be allow to shade out the new seedlings. It will be necessary to do either a quick “flash” grazing pass to take off the top of the grass plants and leave a four- to 4.5-inch residue or a mowing that leaves the same residual height. Once the seedling is established regular grazing or mowing passes can be practiced.
With regard to establishing a new forage stand with a drill, I think we have to look at this year’s weather pattern and what it is doing to soil temperatures. The third week in February we had 50-degree plus soil temperatures at a two-inch depth. As I write this article in early March we have 40-degree plus soil temperatures at a two-inch depth. We are ahead of our average. Seed placed in the soil now is likely to germinate and emerge more quickly this year. That may be okay, but it is early March and we could very well get some low to mid 20 degree temperatures yet. Legumes, especially alfalfa, are susceptible to getting that young seedling killed or damaged by these temperatures because their growing point is above the soil surface. Grasses have a little more protection as their growing point is at the soil surface. So, even though you might be able to drill seed now, from a risk management point of view, it may be best to wait until late March or early April.