Interesting... I just read somewhere (I can't remember where, now... maybe on another forum) that they persist in Zone 9 and lower.
My sister lives in KS, currently listed as Zone 5, but she told me a few days ago that there is some discussion as to rezoning her part of KS to Zone 6. She stopped growing dahlias years ago because they die over the winter there, and she got tired of digging and storing the tubers.
