March is When Alfalfa Lives or Dies

Profile Picture of Post's Author Bill Powel-Smith | Posted March 19, 2023

“March is the month that alfalfa lives or dies”. Looks like 2023 is taking that challenge seriously.

There are a few things that can hurt alfalfa that get determined in March. Why March? Because in March we vacillate between warm thawing conditions and sudden cold, freezing periods. Let’s look at what is helping or hurting alfalfa:

  1. How did alfalfa go into dormancy last fall?
    • What stresses calves in the baking heat of summer and the frigid days in winter? A shortage of energy. Either calves don’t want to eat in the heat or we can’t get enough calories into calves in severe cold. Alfalfa is the same way. These plants need reserves of energy going into winter so they can come out of dormancy in spring and have energy to grow and begin photosynthesis with green up. But that green up is not a straight line. So, the more reserves we have, the more the plant can withstand spring days with clouds or cold and no photosynthesis to produce new energy. Cutting alfalfa in fall without enough time to rebuild energy reserves really sets the plants up for trouble in spring if we get rough weather. Six weeks of regrowth in fall is the rule of thumb. Across the upper Midwest we look at taking a last cutting no later than September 6-10. (Or take a mature late crop that has rebuilt energy reserves later in fall when chance of regrowth and energy draw down of reserves is very, very low.)
  1. What did we have for ground freeze and snow cover this winter?
    • Going into winter in 2022, many places had snow cover before the ground really froze hard. And into 2023 we see many areas with little or no frozen ground. We have seen some snow cover, even after periods of melting which has kept the soil warm enough not to hurt alfalfa. The goal is to keep soil temperature over 20 degrees at 4 inches deep. We did that. Cold temperatures can damage the crowns.
  1. Did we get a January thaw that created ponding and ice sheets?
    • We have had rain, snow, rain snow this winter. Most of this moisture is going down. This is a good thing. The risk of ponding has been low in many areas. And the ponding has been short lived for most. However, some places we have seen ice sheets. Alfalfa roots and crowns in winter still respire, albeit very slowly. Respiration uses oxygen and produces potentially toxic gases like carbon dioxide, ethylene, and methanol. Solid ice prevents the exchange of gases between the soil and the air. Alfalfa plants can die if oxygen can’t get into the soil and the toxic gases can’t escape. Late fall regrowth can help ice covered plant breathe.
  1. How are we emerging from winter; this means what games is the weather playing in March?
    • In March with really frozen ground, the roots get held by the frost while the surface thaws and refreezes. This can snap the root. Or rachet the roots out of the ground – which is called heaving. This heaving can break off tap roots or leave crowns too exposed.
    • In a wet spring like this year, the ground can become saturated. If spring is slow to warm up, we can see crown rot and other root diseases take hold. Roots turn from bright white to tan with blackened streaks. Given enough time, these root issues weaken the plants. You might get a green up but it fades before first crop. Or we get a first crop and the plants struggle after that.

Best course of action is to evaluate (dig) roots and crowns in late April and again in May. Be careful making your alfalfa stand health decision too soon. Things can turn on you based on how the plants weathered the last 6 months.

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