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Alfalfa winter injury: Weather and management effects

Quick facts

  • Weather factors, such as air temperatures, snow depth, and ice sheeting, affect winter survival.
  • Management practices can reduce the risk of winter injury, including variety selection, cutting schedules, and fall harvest dates.
  • Assess your risk of winter injury with the Winter Injury Calculator.

Many factors can contribute to winter injury of an alfalfa stand. There are uncontrollable factors, such as snow cover and air temperatures, but there are also management strategies to reduce the risk of winter injury.

Weather factors affecting winter survival

Winter air temperatures

alfalfa plots showing various levels of winter survival
Alfalfa variety trials showing  varying levels of winter survival.

Dormant alfalfa varieties can suffer winter injury at temperatures ranging from  5 to 15°F.   Winter injury occurs because ice crystals form within and among plant cells and damage cell membranes.

In contrast, periods of warm soil temperatures (more than 41 degrees) in later winter and spring can cause alfalfa to deharden and break dormancy. If followed by extreme cold or icy weather, severe winter injury may result.

Ice sheeting

Ice sheets can develop following snow melt or freezing rain. Ice sheets smother alfalfa plants by preventing air exchange to alfalfa crowns. When this diffusion is restricted, carbon dioxide accumulates around the plants. Normal pathways of aerobic respiration are disrupted and anaerobic respiration predominates. As a result, plants use energy reserves at an accelerated rate and toxic metabolites like ethanol and lactate accumulate. Alfalfa can tolerate up to four weeks of ice sheeting.

Soil moisture

Wet soils in the fall can affect alfalfa's dormancy reaction that reduces free water within and among plant cells. Cellular damage occurs when water freezes. 

Snow depth

Snow depth is critical for insulating the soil. Snow depths of 4 to 8 inches have been shown to provide effective insulation for alfalfa. Snow reflects solar energy and reduces energy absorption that can cause soil warming during the winter.  It can also protect alfalfa from very low air temperatures. As figure 1 illustrates, soil temperatures held steady during the very cold periods of December, 2022, when between 4 and 8 inches of snow covered the ground.  

line graph of air and soil temperatures during the winter at 2 depths.
Figure 1. Minimum air, 2- and 8- inch soil depth temperatures (°F) from November 2, 2022 to January 1, 2023 at St. Paul, Minnesota.


 

Alfalfa management to reduce winter injury risk

As shown in Figure 1, there are many interacting risk factors that affect alfalfa winter survival. Some of those risks can be minimized by management. The most important practices include the following:

Stand age

Older alfalfa stands often have plants with crown injury and disease. Younger stands are healthier and better able to stand winter stress.

Variety selection

Select varieties that are adapted to the soils and climate in a region to ensure the appropriate winter hardiness and disease resistance.

Soil fertility and pest management

Plants stressed pests or by low nutrient levels are weaker and more susceptible to winter injury. Soil test for potassium, phosphorus, and sulfur levels and follow University of Minnesota Extension fertilizer guidelines

Potato leafhopper and alfalfa weevil are the most important economic insect pests of alfalfa. Scout to monitor insect populations and use economic thresholds when treating with insecticides.

Soil moisture

Wet soils can lead to greater freeze-thaw action during the winter and decreases hardening of alfalfa during the fall. Alfalfa should not be grown on soils that retain water or in low-lying areas within a field. Avoid fall irrigation.

Harvest management to reduce winter injury risk

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Winter injury risk

Craig Sheaffer, Extension forage agronomist

Reviewed in 2023

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