July 12, 2012

When temperature is consistently above 90°F, many guidelines for managing alfalfa harvest can be thrown out the window. "Always cut at one-tenth bloom." Gone.

Alfalfa is one of our most reliable crops. We cut it several times each year and it keeps coming back for more. In fact, the plant even tells us when it is ready to be cut. When it begins to bloom, it has recovered from the previous harvest and is ready to be cut.

Or is it? When summer temperatures exceed 90°F every single day like it has much of this summer, it isn't unusual to see alfalfa start to bloom after only twenty-five, or twenty, or even fewer days of regrowth. If it's dry, it may bloom even sooner. Is it really ready to harvest?

The simple answer is "No." High temperatures can cause alfalfa to mislead us about when it is ready to be harvested. Although plants bloom more rapidly when it is hot, it actually takes them longer to recover from the previous cutting than when temperatures are more moderate.

Alfalfa stores nutrients it doesn't need for growth, like extra carbohydrates and protein, in its crown and roots. When alfalfa is cut, it uses these stored nutrients to initiate new regrowth. As regrowth develops, nutrient reserves decline until plants develop enough leaf area to support themselves. Then and only then can extra nutrients be sent into storage. High temperatures, especially at night, reduce the amount of extra nutrients available for storage. So, it takes longer for reserves to return to the same levels as before harvest.

As an added insult, early blooming gives shorter, lower yields that are even worse during dry weather.

Be prepared to break the rules this summer. Even if alfalfa is blooming, be sure to give plants extra time between hot summer harvests to maintain healthy stands.

Bruce Anderson
Extension Forage Specialist