The long-standing recommendation has been to take the last harvest of alfalfa by early September in northern Ohio. The reason is to allow alfalfa plants 4 to 6 weeks growth before a killing frost to accumulate root carbohydrates. We have talked about a critical no-harvest period between early to mid-September and mid-October. Every year I heard comments from some alfalfa growers that the fall rest period is not necessary and fall cutting never harms their stands. So, has something changed that now makes the fall rest period unnecessary? The answer really comes down to degree of risk and risk management.
The fall cutting and rest period considerations developed from research 25-30 years ago are still valid. Cutting is always a stress to the plant. The recommendation to give plenty of time for recovery before winter is still a sound and very safe recommendation, particularly on soils that have less than ideal drainage or where the alfalfa is stressed. However, what has changed in that time period is alfalfa genetics. Today’s alfalfa varieties are better and often have been selected from aggressive cutting management, including fall harvest. Using these improved varieties can reduce, but not eliminate, the risk from a fall harvest before frost. Weather patterns have also changed compared to 25-30 years ago. We are seeing later killing frost dates and that reduces fall harvest risk.
There are other factors that affect the level or risk incurred with a fall harvest. These include overall stand health, variety disease resistance, insect stress on the stand during the summer, age of stand, cutting management, fertility, and soil drainage. Adequate fertility, especially soil potassium levels, and a soil pH near 6.8 will improve plant health and increase tolerance to fall cutting. Stands under 3 years of age are more tolerant of fall cuttings than older stands where root and crown diseases are setting in.
The cutting frequency during the growing season can affect the energy status of the plant going into the fall. Frequent cutting (30 day intervals or less) results in the plant never reaching full energy reserve status during the growing season. This makes the critical fall rest period more necessary for plants to accumulate adequate reserves before winter. So a fifth cutting taken in the fall carries more risk than taking a fourth or third cutting during the fall.
Soil drainage is a factor. Alfalfa stands on well-drained soils tolerate later fall cuttings better than alfalfa on moderately or poorly drained soils. Low plant cover going into the winter from late cutting increases the risk of winter heaving on many Ohio soils.
Finally, are you certain that it is not harming your stand productivity at all? Have you made a side-by-side comparison to see if there is a difference? If not, then try it this year. Leave some strips that you don’t cut when you take a fall cutting this year, mark those spots and look at them carefully next spring compared with where you did cut in the fall.