Prepare your alfalfa for winter

As summer comes to an end and temperatures cool, it is time to start preparing the stand for winter.

How an alfalfa field enters winter can have a major influence on its ability to survive cold temperatures and produce forage the following spring. Fall management is especially important in the Upper Midwest, where alfalfa can be exposed to freezing temperatures, ice formation, snow cover, saturated soils, and rapid temperature changes. The goal of fall management is not simply to produce one more harvest. It is to balance the value of late-season forage with the need to allow plants to build reserves and develop adequate winter hardiness.

Why does fall management matter?

Alfalfa stores carbohydrates and other reserves in its crown and roots. These reserves help the plant survive winter and support regrowth in the spring.
As plants approach dormancy, they gradually allocate resources to their crown and root systems. Management practices that repeatedly remove plant tissue late in the season can interfere with this process.

Consider the timing of your last harvest

One of the most important fall decisions is whether to take a final harvest and, if so, when.

When deciding whether to make another cutting, consider:

How much regrowth is currently present?

Alfalfa needs sufficient leaf area to photosynthesize and replenish carbohydrate reserves below ground (crown and roots) before the first killing frost. 

How much time remains before the first killing frost?

The recommendation is to allow at least 5 to 6 weeks, or more than 900 growing degree days (GDDs, base 41ºF) between the last cut and the first killing frost. This interval allows plants to regrow and replenish crown and root carbohydrate reserves needed for winter survival and spring regrowth. Alternatively, harvesting within approximately two weeks of the expected killing frost (less than 360 GDD remaining) is another option, as the plant will not have enough time to regrow and will conserve reserves for winter maintenance and spring growth. 

What temperatures are expected over the next several weeks?

Monitor local weather forecasts and historical frost dates to estimate how much growing time remains. A frost occurs when temperatures drop below 32ºF, but for a killing frost, the temperature must drop below 24ºF for a few hours. Actual temperatures and the timing remaining before a killing frost are important considerations when evaluating whether another cutting is worth it.

You can check the weather data for your area with the Minnesota Climatology Office.

Newly established and older stands are generally more vulnerable to winter injury when harvested late in the fall. Assess stand vigor and overall health before deciding whether another cutting is worthwhile.  

Are other factors increasing the risk of winterkills?

Poor drainage, ice formation, and limited snow cover can increase the risk of winter injury. Poor drainage can contribute to ice formation, creating a barrier between the soil and the atmosphere that restricts gas exchange. This can cause carbon dioxide to accumulate belowground, reduce oxygen availability, and contribute to plant asphyxiation. 

When is the first killing frost likely to occur, and what temperatures can alfalfa tolerate?

A killing frost is generally associated with temperatures below 24ºF for a few hours, although the actual impact depends on the duration of freezing temperatures, plant acclimation, and field conditions. The number of hours below freezing and the severity of the cold can influence plant responses. Therefore, consider both the expected minimum temperature and the duration of exposure when assessing the risk of late-season harvest. Consult the Minnesota Department of Natural Resources Fall Freeze and Frost Date Probability and local weather forecasts to help estimate frost timing.

Does the field have a history of winter injury or winterkill?

Previous stand information can help identify where late-fall harvest should be approached cautiously.

It is worth noting that not all alfalfa fields enter winter with the same level of risk. Several factors can increase the likelihood of winter injury or stand loss, including young or poorly established stands; older stands with declining plant density; alfalfa variety winterhardiness score; soil drainage; pH; and soil fertility. 

Fields with multiple risk factors deserve particular attention during the fall. Calculate your risk of alfalfa winter injury.

What about snow and ice?

Snow can provide insulation and protect crowns from extremely low temperatures.

Leaving an unharvested stubble height of 4 to 6 inches can help trap and retain snow, providing additional insulation. However, prolonged ice encasement can create additional challenges because it can restrict gas exchange and contribute to winter injury. Because winter conditions cannot be controlled, the best strategy is to enter winter with a healthy, well-established stand with adequate reserves.

The goal is a healthy stand next spring

Fall management is ultimately an investment in next year’s crop.

The decisions made now can influence how well alfalfa survives the winter and how quickly it resumes growth in the spring. We cannot change the weather, but we can change the stand management.