Interesting outcome. In February, we had 20-ish temps for a day or two. I thought that beets were pretty tolerant of that, but most of the foliage was killed. I figured I'd have to replant, but decided to wait a week or two to see what happened. They ALL resprouted leaves, and in a month or so had full foliage, and the beets were increasing in size. Now that I'm harvesting, I notice that the beets (while full sized, and delicious) are a bit odd. Instead of one big clump of foliage coming out of the top, the foliage sprouted out all around the sides of the beets, and trimming foliage takes a bit more work. So I guess the going-forward strategy in a very hard freeze is to protect them, and try to preserve the on-top foliage.