Why frost seedings fail

Frost seeding is one of the most economical ways to improve pastures. Avoid these pitfalls for better success.

March is the month when many landowners frost seed improved clover and other seed varieties onto pasturelands to improve the pasture quality and yield. Various research trials have shown that when done properly, frost seeding can be a very low-cost, environmentally friendly way to improve pastures. However, these attempts do not succeed every time. Let’s look at some of the reasons why frost seedings fail in order to avoid some of these pitfalls.

The primary reason for failure, and one that is totally unavoidable, is weather related. The lack of adequate rain in early summer is one of the most common reasons why the new seedings do not show up. In frost seeding we are putting the new seedlings into a very hostile environment. We have not killed, nor tilled back the existing forage base in the pasture and it quickly becomes survival of the fittest. If rain does not fall on a fairly regular basis in late May through June when the new young seedlings are trying to extend their roots down as deep as the established grasses, these young seedlings will quickly wither and die, especially if the weather turns hot and dry.

Attempting a frost seeding on sandy soils usually does not turn out well. For one, we need the late winter heaving action of the soil to help cover the seed on the soil surface. Sandy soils do not move enough for this action to occur. Add on to that the fact that sandy soils tend to dry out easier without adequate rainfall and it is easy to understand why sandy soils are not good candidates for frost seedings. On sand-based soils it is better to direct drill with a no-till drill or even a conventional grain drill seed into the sod in April when the sod is still moist and the tractor can still get safely across the field without excessive wheel track damage.

Frost seedings on well managed pastures also tend not to turn out as well, mainly because there is too much competition already there. Managed, intensive graziers sometimes say they use to get frost seeding to work, but have not had much success lately. Many have improved their grass sods enough that the thatch layer is thick and the grass is competitive enough that the broadcast seed may never reach the soil, or if they do they cannot compete with the strong sod base. These graziers have to determine if they really do need to improve their pasture more, and if so, either stress the stand a lot more with grazing the fall before, or else use a different seeding method.

Also, graziers with better stands may need to be a little more patient. Many of the legume seeds, especially in situations with strong thatches covering the soil, do not have all the seed germinate the first year. More may show up the second or third year after seed has finally gotten in contact with the soil. Some have seen this phenomenon occur and have trouble understanding why.

Seeding too early or too late can also have detrimental effects on seeding success. Seed too much before the 45-day window before grass growth begins, and you put the seed at risk for a longer period of time to be washed away. Snow melts or large rainfall events, especially on frozen soils, can wash portions of the seed long distances from where they were spread. Seeding too late with an early spring, extended warm period can leave the seed on the soil surface for too long, drying the seed out and potentially killing the inoculant bacteria on the seed.

Speaking of inoculants, not having the specific bacteria inoculant on the legume seeds of red clover, white clover, or birdsfoot trefoil can cause the seedlings to not produce enough nitrogen to survive the first summer. Normally these legumes come pre-inoculated at the seed mill, but they are living bacteria and if they are not handled properly they may not survive long enough to make a difference in the field. If the date on the seed bag tag is over six months old, the inoculant may not be viable. Also, if the seed bag were kept inside in warm temperatures (above 70 degrees F) for weeks, the inoculant again may have dried out and died. If you are ever unsure about the viability of the legume seed inoculant, it is cheap insurance to purchase an extra supply of appropriate inoculant and inoculate it again.

Once the new seedlings start to grow, proper grazing management is also important. All seedlings need a chance to grow free from grazing animals. They can compete with some grass pressure as the grass grows taller. But when this competition becomes too great (usually at 8 inches of grass height), the animals should be turned in and all forage, including the new seedlings, should be grazed down tightly. Then the animals should be removed and the seedlings allowed to grow again. This rest and then graze sequence is much better for the new seedlings than constant grazing pressure.

Finally buying cheap seed is another cause for some failures of frost seedings. Some feel that frost seeding is a risky proposition and do not want to invest any more money than they have to, so they buy the cheapest seed available at the local mill. This may be out-dated seed. Or it may be pasture mixes that have more grasses that will not frost seed well than legumes that will. Or they may be less hardy varieties that just will not compete well in a frost seeding environment. Often the decision is made to frost seed in mid-March as the window of opportunity for the season is running out and the only seed available locally is one of the cheap, less hardy varieties mentioned above. Our best advice is if you are going to make the effort to frost seed, purchase the seed that has the best chance to succeed and purchase the best you can find. It does make a difference.

Frost seeding, when it does work, is one of the most economical ways to improve pastures. Avoiding some of the pitfalls mentioned above can make it be successful more often.

For more information, contact MSU Extension Grazing Educator Jerry Lindquist toll-free at 888-678-3464, extension 6723, or at lindquis@msu.edu.

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