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Predicting alfalfa winter survival?

Craig Sheaffer, Extension forage agronomist

Alfalfa variety trials showing varying levels of
winter survival.
This winter has been remarkable in many ways. In contrast to the 2022-2023 winter, much of the state has received 50% or less of the normal snowfall, and each month we have had record high air temperatures. There have also been wide swings in air temperatures.

But most importantly for alfalfa, the 2-4 inch soil temperatures have been in the mid- 20’s to mid-30’s throughout the winter. Even on 28 February, when morning air temperatures plunged to near 0 F, 2- 4 inch soil temperatures were near 30 F, nowhere near the temperatures of 5-15 F that can injure alfalfa. 

For more details on Minnesota weather and soil temperatures, visit 

Alfalfa winterinjury

A diversity of winter conditions can cause a significant risk to alfalfa persistence. We have therefore over time written several articles about winter injury and its effects. This includes an article written in 2023 where we raved about the importance of snow cover for alfalfa winter survival. But that was last year, and this year is really different. For more insight on winter injury and its evaluation see:

How’s alfalfa doing this winter?

Energy reserves and cold resistance of winterhardy alfalfa varieties are normally greatest in December to January and then slowly decrease till March when dormancy is broken as soil temperatures climb. Several days of soil temperatures of 41F and above are required for dormancy to break. Once broken, overwintering crown buds that formed become vegetative and elongate. We typically begin to see regrowth during April.

This is a different year, and we will likely see alfalfa shoots by mid-March. Some south facing stands that warm up sooner will like to emerge earlier. But so far alfalfa should be in great shape throughout most the state. There are several factors to consider:
  • Alfalfa had a long fall dormancy reaction period that lasted from September to nearly December. During this time, until air temperatures reached >22F for several days, some small leaves were visible near the soil surface and the plant had potential to continue to store energy.
  • Dry soils during the fall and winter in major producing regions decrease free water in the plant and enhanced winterhardiness.
  • Soil temperature in the top 2-4 inches remained in the 20- 30’s for most of the winter. Even with warm air temperatures, soil temperatures in the top 2-4 inches have not reached 41 F in many parts of the state. Because of the day-night fluctuations, we have not accumulated enough growing degree days or heat units above 41 F to break dormancy and awaken crown buds.

The biggest risk to alfalfa winter survival: fluctuating air temperatures.

If warming air temperature trends continue and alfalfa breaks dormancy, there is a risk of significant frost damage, should we have minimum air temperatures of 24 F or less. New regrowth would then need to come from newly formed buds. Spring damage to alfalfa is described in  Frosted alfalfa.

Another risk associated with fluctuating temperatures is from heaving of the roots and crowns of alfalfa’s tap root. Heaving is a volumetric expansion of the soil caused by the segregation and expansion of frozen water (ice) in the soils. Heaving injury results in breaking of the tap root, shearing of lateral roots, and exposure of crowns above ground. For more details, see Winter hazards to forages: Heaving 

Decreasing risks of winter injury:

There are several management strategies applied in 2023 that reduce the risk of winterinjury this spring. These are detailed at:
The most important of these this year are fall cutting and variety selection.
  • Unharvested stubble. Alfalfa stems and leaves remaining in the field are valuable to buffer the soil against winter soil warmup when air temperatures rise. In recent measurements we have taken, soil temperatures under unharvested stubble were 5 F less than bare soil where fall harvests occurred. This is beneficial in delaying premature breaking of dormancy.
  • Variety winterhardiness and fall dormancy. Varieties are characterized for winterhardiness, fall dormancy and disease resistance. Varieties grown in Minnesota should have a winterhardiness of 1 or 2. This year fall dormancy reaction may be especially important in protecting alfalfa from late season winterkill because varieties with greater fall dormancy are slower to emerge from dormancy in late winter than less dormant varieties. Therefore, although some marketed varieties are FD5, there is less risk with varieties of FD2, FD3, FD4. For information on alfalfa varieties see the National Alfalfa & Forage Alliance's: Alfalfa variety ratings.

Should we do early spring seedings this year?

With the higher-than-normal air temperatures and dry soil conditions, there may be opportunities to seed earlier than normal this year. We have been proponents of early spring seedings to maximize seeding year forage yields. Early planting allows seedlings to take advantage of spring moisture conditions, compete better with weeds, and provides a longer growing season with the possibility of three harvests in the seeding year. Seedlings from cotyledon to unifoliolate leaf stage are tolerant of air temperatures as low as 24 F but are killed at 20 F, because they have not developed crown and root systems. Normally air temperatures of 24F or less are unlikely after early May, but there is still some risk given the extreme air temperature fluctuation we have seen.

For more information, see Alfalfa seedling tolerance to freezing temperatures.

Some key points:

  • There is potential for no alfalfa winter injury this year. Even with lack of snow cover, because of above normal air temperatures, 2-4 inch soil temperatures have consistently been in the 20-30 F range, above the 5-15 F temperatures associated with winterkill.
  • Residue left in the fall plays a significant role in reducing early soil warmup and premature breaks in dormancy which is stimulated by soil temperatures above 41 F.
  • The greatest risks to alfalfa survival are due to fluctuating air temperatures. If alfalfa breaks dormancy, there is a risk of significant frost damage to herbage, should we have periods of minimum air temperatures of 24 F or less.

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