The end of 2025 brought early snowfalls, then January delivered extremely cold temperatures for an extended period. I’m sure there are growers out there wondering what this weather will do to the alfalfa. This is a good time to review causes and recovery from winterkill in alfalfa.
Winterkill can be hard to predict because alfalfa can fail to survive winter for several reasons. The most common is alfalfa being killed when water in the plant freezes, causing the cell walls to rupture. Alfalfa can also 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 8″ 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 leave at least 4″ of stubble, important for catching snow and allowing the plant to discharge toxins. Reflecting on these management guidelines, how well did you do setting up the alfalfa for overwintering success?
Following proper management guidance can help a lot in preparing your alfalfa for winter, but the weather is out of your control. A wet fall will leave more water in the plants, making them more vulnerable to freezing injury. Two weeks of temperatures between 5°F and 15°F will kill most varieties. Snow cover can do a lot to shelter your plants, as it is a great insulator and will keep soil temperatures from dropping to these lows. Snow by itself will not smother alfalfa, since air will continue to flow through the layers of flakes.
Following proper management guidance can help a lot in preparing your alfalfa for winter...
Sometimes high temperatures can be a bigger problem. Temperatures above 40° 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 temperatures can bring rain and melt snow, potentially turning it into ice sheets that cover large areas of your alfalfa. Ice sheets do and will smother plants; this is probably where we have seen the most damage over the last several years.
Winterkill in young stands (following the seeding year) is fixable by reseeding or interseeding new seed. With older stands, you have two options: 1) live with what you have left or 2) rotate out of alfalfa. Plants in older stands secrete autotoxins into the soil, which 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.
My concern in 2026 is for acres that lacked sufficient snow cover and were fully exposed to the harsh January temperatures.
How predictable is winterkill as we sit in the middle of the winter? I would say not very. In your own area, you can monitor the potential weather risks – extreme temperatures, lack of snow cover, and saturated soils with ice. My concern in 2026 is for acres that lacked sufficient snow cover and were fully exposed to the harsh January temperatures. Hopefully, we will see all our alfalfa make it through to spring!
