With forage supplies tight in some areas this year, getting one more cutting from an alfalfa field may be tempting. While that extra hay can be valuable, we also need to think through what a late harvest may mean for stand health this winter and productivity next spring.
Traditionally, we’ve recommended giving alfalfa roughly six weeks of uninterrupted growth before a killing freeze. The problem with a calendar recommendation is that every fall is different. Growing degree days, or GDD, give us another way to look at that decision.
There has also been an important correction to numbers I’ve shared in the past. Previous recommendations used 500 and 200 growing degree days with a base temperature of 41 degrees. A review of the original research found those values were based on Celsius GDD and weren’t properly converted to Fahrenheit.
Using base-41 Fahrenheit, the numbers we should be using are about 900 and 360 GDD.
If more than 900 GDD remain between harvest and a killing freeze, alfalfa should have enough growing weather to regrow and replace the reserves it used. Once fewer than 360 GDD remain, there generally isn’t enough time for much regrowth to occur.
That leaves 360 to 900 GDD as the window we want to avoid. Cutting during that period can trigger regrowth and use stored energy without leaving enough growing season for the plant to fully replace it.
Stand condition also needs to be part of the decision. Older or thinning stands, or fields stressed by drought, insects, disease, poor fertility, or frequent cutting, would benefit from more conservative management.
So how do we know where we stand?
For eastern Nebraska, the University of Wisconsin’s Alfalfa Cutting Tool can help. Select the Upper Midwest map, choose your location, and click the Season Planning tab. Right now, coverage only extends into roughly the eastern quarter of Nebraska.
Farther west, the High Plains Regional Climate Center’s CLIMOD tool can be used to look at historical base-41 GDD and killing-freeze dates for nearby locations.
Remember, these tools are still based on historical weather, so they should be used to evaluate risk rather than as a guarantee.
Getting the crop cut is only part of the challenge. Cooler temperatures, shorter days, and heavier dew can make getting hay dry increasingly difficult as we move further into fall.
If you do take a late cutting, consider leaving four to six inches of stubble. A higher cutting height can improve airflow under the windrow and help with dry down while also leaving more residue to catch snow and provide some winter protection.
There may be a few secondary pest-management benefits to removing late-season growth, but I wouldn’t take a late cutting simply to clean up a field. Stand health and timing should still drive the decision.
If you need some extra feed this winter, don’t just look at the calendar. Look at stand condition and the growing weather we have left. Ideally, cut with more than 900 GDD remaining before a killing freeze, or wait until fewer than 360 remain and very little regrowth is expected.
Ben Beckman is a livestock systems Extension Educator based out of the Cedar County Extension office in Hartington, serving northeast Nebraska. You can reach him by phone: (402) 254-6821 or email: ben.beckman@unl.edu.
