Fall Harvesting Alfalfa - Frequently Asked Questions

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 Is there a critical fall period when alfalfa should not be harvested?
Alfalfa should not be cut 4-6 weeks before the first killing frost (about -5oC). Shorter days, cooler temperatures, and drier soils trigger the plant to slow growth and begin storing root reserves for the winter and growth the following spring. If alfalfa is cut during this period and begins to regrow it will need to use root reserves. If a killing frost occurs before root reserves are restored (10” or bud stage), then the plant may not have enough reserves for the winter and spring regrowth.

Will I injure my newly established stand if I cut it now? Wouldn’t it be better to cut the older ones?
Actually a newly established stand of alfalfa is less likely to be injured that an older stand (3 years and older). Younger stands are healthier and are free of the crown and root diseases. The available nutrients are also higher in younger stands and improve winter survival. However, if you do harvest a stand during the critical fall period, do not repeat this practice the following year.

Can fertility improve winter survival?
Fertility is a very important part of winter survival. Alfalfa can fix nitrogen, but it will still require large amounts of the other nutrients. Potassium (K) helps protect the plant tissues from freezing, plays a role in storing winter reserves, and improves resistance to diseases. Phosphorus (P) will help establish strong root systems and promote vigorous spring growth. The most efficient way to provide these nutrients is at the time of establishment.

What other factors affect winter survival?
Variety, fall moisture conditions, and soil pH will all have a role in winter survival.

Not all alfalfa varieties are the same with regard to winter hardiness. Remember that rapid growth and yield will usually come at the cost of winter hardiness.

Soil pH is also important. Alfalfa is best adapted to a soil pH of 6.5. Stands grown in slightly acidic soils (less than 6.0) will be at a greater risk for winter injury and should not be harvested during the critical period.

Wet field conditions in the fall will reduce the amount of dormancy and increase injury from ice sheeting and frost heaving. Dry soils are actually better insulated and hasten the onset of dormancy which will improve winter survival.

Which is the safest way to harvest alfalfa in the fall with out injuring the plant?
The best solution would be to wait until just before or after the killing frost. Alfalfa will be difficult to dry under these conditions so it is advised to ensile it. If you can, leave a 6 in. stubble and some uncut strips to help trap snow. Alternatively, you could try and move up your first cutting date (again you may have to silage it to beat the weather) so that your second cut will fall just before the critical period.

Prepared by Mark Johns, Ag-Info Centre, Alberta Agriculture and Forestry

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This document is maintained by Marie Glover.
This information published to the web on August 13, 2003.
Last Reviewed/Revised on February 6, 2018.