This winter’s weather harkens back to the days of my childhood when we used to get a lot of snow in Southern Wisconsin. We have had snow on the ground for two months already and we still have all of February ahead of us. It seems like every three days we have gotten a snowstorm with a few rains just for good measure. I’m sure there are growers out there wondering what this weather is going to do to their alfalfa. This might be a good time to review causes of and recovery from winterkill in alfalfa.

Winterkill is hard to predict because alfalfa can fail to survive winter for several reasons. The most common reason is alfalfa being killed when water in the plant freezes, causing the cell walls to rupture. Alfalfa can suffocate if it can’t clear toxic metabolites in the winter. Another cause of failure occurs if alfalfa comes out of dormancy in the winter and uses up its root reserves before spring comes. The last common failure is soil heaving, forcing roots out of the ground or damaging their structure.

Winter survival starts in the fall.  Having good root reserves is the first step.  At roughly eight inches of growth the alfalfa plant starts storing reserves in the roots and crown, reaching full reserve potential when the plant is at full bloom.  Target 25% bloom for that last cut (or after a hard frost) to provide sufficient root reserves. Also avoid cutting in September and early October to protect the plants from using up reserves needed for re-growth in the spring.  The last cut should also leave at least four inches of stubble; important for catching snow and allowing plant to discharge toxins.

Following proper management guidance can help prepare your alfalfa for winter, but there are things that are out of your control.  A wet fall will leave more water in the plants, making them more vulnerable to freezing injury.  Two weeks of 5-15 degree temperature will kill most varieties. Snow cover can do a lot to shelter your plants from this as it is a great insulator and will keep the temperatures at the soil level from hitting these lows. Snow by itself will not smother alfalfa as air will continue to flow through the

layers of flakes.

Sometimes high temperatures can be a bigger problem. Temperatures above 40 degrees can cause alfalfa to break dormancy, eating up root reserves and making the plant more vulnerable to freezing later in the winter. These spikes in winter temperature can bring rain and melt snow, which have the potential to turn into ice sheets covering large areas of your alfalfa. Ice sheets do and will smoother plants; this is probably where we have seen the most damage over the last several years.

Winterkill in young stands (following seeding year) is fixable by reseeding or inter-seeding new seed. With older stands you have two options: 1) living with what you have left or 2) rotating out of the alfalfa. The problem with older stands is that these plants will secrete autotoxins into the soil that will prevent new seedlings from establishing or severely stunt them. Based on soil structure, the autotoxins can remain in the soil for a year or more after the old stand is plowed up.

So how predictable is winterkill as we sit in the middle of the winter? I would say not very. Locally our biggest threat is ice sheeting. In your own area you can only look for the signs – extreme temperatures, lack of snow cover and saturated soils with ice. Hopefully will see all our alfalfa make it through to spring.