Conventional wisdom has long held that it’s best to not harvest alfalfa during a critical period running four to six weeks before the first killing frost. But with more disease-resistant and winterhardy alfalfa varieties and current favorable hay prices, some growers are rethinking the old advice, notes Penn State University forage specialist Marvin Hall. He advises considering the following when deciding whether to take a fall cutting during the so-called critical period:

Age of stand. Older alfalfa stands are more likely to winterkill or suffer winter injury following a fall harvest than younger alfalfa stands.
Variety. Alfalfa varieties with moderate resistance to several diseases and sufficient winterhardiness have greater tolerance to stress from fall harvesting than less disease-resistant or winterhardy varieties.
Soil pH and fertility. Adequate soil pH and fertility minimizes the risk of fall harvesting by allowing alfalfa plants to develop properly and be healthier.
Soil drainage. Alfalfa on well-drained soils is less likely to suffer winter injury than alfalfa on poorly drained soils.
Harvest frequency. A harvest schedule that doesn’t allow the alfalfa plant to flower once during the season predisposes it to winter injury.
Dry conditions in August. Dry weather, especially in August, causes alfalfa to store excess root energy reserves, making it more winterhardy.
Fall cutting height. Leaving 6-8” of stubble when taking a fall harvest will reduce the risk of winter injury.