I live in zone 5b, and have alot of basjoos which I've protected under straw piles for the winter. Howeve, as an experiment, I transplanted a 2 1/2' pup in september, (late) and didn't mulch it when winter came on. When it frosted, It blackened, and toppled. I just left it laying there, and the stalk shriveled up and looked dead. Lo and behold, this morning I noticed a fresh shoot sticking up out of the ground at it's base. I'm kind of impressed by this thing's pluck.