Fall Harvest Management of Alfalfa

Fall harvest management of alfalfa can affect winter survival of alfalfa stands. Harvesting alfalfa between August 15 and the first killing frost results in depletion of root reserves and increases the chance of winter injury.

After alfalfa is cut, root reserves are used to initiate top growth. Root reserves are at their lowest when plants reach 6 to 8 inches tall and are fully replenished at the point where the plants are in the full bloom stage. If killing frost occurs at the 6 to 8 inch height replenishment of root reserves is curtailed and winter injury can be expected.

Sometimes there is an opportunity to take a second or third cut after killing frost has occurred in late September or early October. There is little growth after a killing frost and removal of forage will have little effect on the level of root reserves, provided that plants have become dormant.

For stands cut in the post frost period, leaving strips of uncut alfalfa to catch snow and insulate crowns from cold winter temperatures can improve winter survival. Leaving a small strip of standing alfalfa every 40 to 50 feet will usually allow enough snow to accumulate and insulate the crop from cold winter temperatures.

Other factors influencing the chance of winter injury include potash fertility, age of the stand, fall dormancy rating of the variety, and soil moisture levels. Where soils test lower than 120 ppm in potassium, alfalfa winter survival will improve if potash fertilizer is added. Potash fertility and fall cutting management are the largest management factors that allow long term productivity of alfalfa.