Harvesting Alfalfa Hay
The time to cut Alfalfa has traditionally been recommended to be at 1/10th bloom, meaning when only 1/10th of the blooms have opened. Jim Shroyer, K-State Extension agronomist, says "cutting should be based on crown regrowth rather than bloom."
It is difficult to know when the Alfalfa is 1/10th in bloom. Most people want to wait until the field looks purple before cutting. 1/10th bloom will be reached before the field looks purple. By the time the purple color shows the regrowth may already be high enough that it will be cut when the hay crop is harvested and the plant will need to start growth again for the next cutting. This will deplete the alfalfa food reserves and delay the next cutting.
Shroyer says crown regrowth is a more accurate gauge than bloom.
After the first cutting, the timing of cut can be based on 1/10th bloom, or 25- to 32-day intervals, unless disease or insect damage causes leaf loss.
"If lodging, insects, disease or drought causes excessive leaf loss, you may have to make an unscheduled cutting." If so, make a cutting to salvage the hay crop and maintain the stand, and then delay the next cutting until the plants have recovered and replenished their root reserves.
From the Kansas Forage Publications Database: - Timely Cutting of Alfalfa