According to the National Climatic Data Center, the average date for the first frost in the area is October 13th. The Washington Extension Office and ISU Extension and Outreach is advising that frost injured alfalfa, clovers and perennial cool-season forage grasses are not considered toxic and do not form hydrodynamic acid. They can be grazed or harvested following frost, and there is a slightly higher risk for bloat in the first few days after a frost.
It is also advised to leave alfalfa plants uncut and standing through the winter if not needed. Although, if the forage is needed, harvest as soon as possible following a killing freeze, a 23-degree freeze that lasts for 4 to 6 hours.