Alfalfa Harvests in High Heat

Alfalfa Harvests in High Heat June 28, 2018

When the temperature is consistently above 90°F, many guidelines for alfalfa harvest, like cutting at one-tenth bloom, should be thrown out the window.

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 often 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—as they have much of this summer—alfalfa may start to bloom after only 25, 20, or even fewer days of regrowth. If it’s dry, it may bloom even sooner. Does that really mean it's ready to harvest?

The simple answer is "No." High temperatures can cause alfalfa to mislead us. 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 it's cut, it uses these stored nutrients to initiate new regrowth.  As regrowth develops, nutrient reserve levels 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.  It will take longer for reserves to return to the same levels as before harvest.

In addition, early blooming gives shorter, lower yields that are even worse during dry weather.

To get the most from your remaining alfalfa harvests, don't rely on blooms to determine timing. Give plants extra time between hot summer harvests to maintain healthy stands.

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