Some varieties can come back from roots after 10 degrees F. When I lived near St George,SC, people were growing a purple variety for syrup that did fine. Harvested in Fall and often not even mulched and came back year after year.... From what I remember, some varieties are much more tender to frost than others ,you could just harvest before a hard freeze and replant some stalks in Spring. There are some types better for chewing and others for processing.