With a week of warmer-than-average temperatures displayed on my weather app following a sub-zero cold snap, I’m a little concerned about alfalfa injury and winterkill. This isn’t the first time temperatures have dipped and risen in my area this winter, nor has there been significant snow cover to protect plants from the fluctuations.
The same concern seems to exist in other parts of the country where similar patterns of extremely cold temperatures have been interrupted with periods of warm weather. In a recent article from Ohio State University Extension, a team of field specialists say this type of variation is what instigates alfalfa heaving.
The authors explain that when rain or melted snow infiltrates the soil profile, it expands as it refreezes, lifting the upper layers of soil and established plants along with it. This is the same phenomenon the causes potholes to grow larger on paved roads during the winter.
When alfalfa is forced above the surface with expanding soil, exposed crowns are subject to damage, especially if temperatures tank after heaving occurs and there is no snow cover to insulate the ground. Deep-rooted taproots may also be broken since they can’t move upward with heaved plants.
When taproots break, alfalfa can be slow to green up in the spring, as these are the storage systems for the energy that initiates early season growth. The authors add that the breaking of crucial fine roots can inhibit alfalfa’s ability to take up water. In many cases, heaved plants may start to green up, but when the top couple inches of soil dries out as the season progresses, alfalfa may start to die after a few weeks.
Recovery or reseed
Alfalfa heaving, and alfalfa winterkill in general, remain somewhat of a mystery. Even under the defined conditions, heaving and winterkill may not occur. On the other hand, taking preventative measures — like leaving ample stubble after fall harvest to retain snow cover and reduce standing water — might not be enough to protect plants in the long run.
The authors note well-drained alfalfa stands typically have less incidence of heaved alfalfa. Seeding well-adapted varieties and optimizing soil fertility may also help mitigate heaving; however, there is no way to completely ward off the risk.
With that said, if heaving occurs, assessing stands and identifying affected areas sooner than later will allow more time to determine the next steps this spring. Where mild to moderate heaving occurs, the authors suggest delaying first cutting to give root systems a longer recovery period. Then, raise the cutting height to protect the crowns of the heaved plants. They add that spring rains can help settle plants back into the soil, although this can disguise taproot damage.
Do not attempt to push heaved alfalfa back into the ground with a roller or cultipacker. In severe cases where more than 20% of plants in a stand are damaged, the authors recommend terminating the stand and planting annual forages.
