It’s Time to Start Thinking about Frost-Seeding Legumes

Victor Shelton, Victor Shelton, NRCS State Agronomist/Grazing Specialist
(Previously published in On Pasture: January 18, 20120)

Frost seeding is one of the least expensive ways to enhance the stand of legumes in your pastures. It is basically the process of broadcasting the legume seed onto the soil surface during the winter dormant months and letting nature do the rest of the work.

Frost seeding relies on the freezing-thawing action of the soil, which is honeycombing the soil surface with ice crystals. The soil surface expands and contracts, allowing the small seed to find a route into the ground. During warmer winters, you might not always get enough action, leaving the seed uncovered. The seed lying on the soil surface can be warmed enough by the sun to initiate germination, only to be killed by the next freeze. When the seed is protected by the soil it is not as likely to be impacted by the sun and is more likely to wait until the proper time to germinate.

In our area of Indiana, the ideal time is usually somewhere between Christmas and Valentine’s Day. And, if I really had my choice, I’d wait for a light snow on the ground and then do the sowing. The snow serves two good purposes. One, it helps “catch” the seed and transport it to the ground and two, it serves as a great marker for the tractor or ATV.

Competition is probably your next worst enemy for planting survival. Broadcast seeding or frost seeding into a heavy stand of grass usually results in less success. So, if you know you are going to be frost seeding legumes into a pasture, wait until after the forage has become dormant and then graze it down to about 3-4 inches to remove any excess growth. This will help the seed find its way to the soil surface and wait for that freezing action. Grazing closer to the soil surface also helps slow early spring growth of the grass so the legume seedling has a fighting chance.

That reminds me to mention, don’t hit those newly seeded fields with nitrogen in the spring either.  All this does is promote the grass growth in the sward and reduce those new legume seedlings’ chances. They won’t have the root base or energy stored up to compete with established grass, especially with grass that has a boost of nitrogen!

What should you plant? Consider Clover
Clovers are probably the easiest legumes to frost-seed. The seed is small and slick and easily moves down through the residue/residual to the ground. If you already have some clover and are just enhancing what you have, then utilize improved varieties for the best results. If you don’t have any clover presently, then you should inoculate the seed with the appropriate rhizobium. The seed may germinate and thrive without it, but it will do so much better if it is present, especially if one of the goals for planting the legume is as a nitrogen source for the grass component of the stand

It is best to get a seeding recommendation and rates for the legumes from your local soil and water conservation district office or extension office. Some legumes do better with particular types of livestock over others, some do better depending on the type of soil and drainage, and there are some differences depending on management. Red clover for example is better suited for hay than most white clovers because it dries better. There is also a huge difference in seed size which highly influences the amount of seed that is needed. Most white clovers have over three times more seed per pound than red clovers. It is easy to seed too much white clover and seed size is part of the reason.  That can be a problem because white clovers (Dutch whites, Ladinos, Alsike, etc.), can cause bloat issues when they dominate a stand.

You can buy clover seed coated too. Coated seed has a coating of clay material surrounding the seed which actually helps you be able to sow very small seed more accurately. It does change the pounds of bulk seed you are planting. Most coating adds about 33-34% inert ingredients to the bag of seed. So if you are wanting to plant six pounds of red clover, you are actually going to have to increase the amount of bulk seed you plant per acre to about nine pounds per acre to get your planned six pound rate. Most legumes have good germination and purity rates normally, but that does vary some. The inert ingredient percentage needs to be accounted for with the purity. For example a lot with 98% germination and 97% purity with 33% inert (the coating) .98 x .97 x (1-33% or .67) = .63 (or 63%) of the lot is live seed. So if the desired pure live seed rate is six pounds per acre, 6 / .63 = 9.5 pounds per acre. When it comes to something like a Ladino clover and you are wanting to seed only about a pound per acre in some cases, coated seed makes it a lot easier to do.

Coated seed can also be the carrier of the inoculant if needed and occasionally has other things included. If you really need the inoculant, the seed needs to be used the same year it was coated. Quite a bit of legume seed has a calcium carbonate coating which can create a slightly better environment pH wise for the sprouting seed, but for the plant to thrive and do well, low pH soils should be limed at least six months in advance to create the environment best suited for the legume being present. Most clovers like a soil pH of 6.2 to 6.8 with preference on the upper end of that range.

And About that Residue/Residual
Earlier I included residue/residual in a statement and there is a reason I did that. Just recently, Jim Gerrish’s article last week in On Pasture noted that we need to be more careful of the use of these two words in regards to the forage left in the pasture after a grazing episode. I totally agree and thought this statement was excellent! I try to stick to these same definitions and if I have ever deviated from this, I apologize.

So, with that said, how is the residue and residual in your pastures today?

Keep on grazing!