I'm buying some for my food forest in zone 4a. I'll put them in a protected place. The nursery I'm getting them from is in zone 5a and they are curious how they'll do for me. They said that they get some tip die back on theirs when it gets to -20F. If you're interested, their name is Reeseville Ridge Nursery.
"Hundreds of years from now it will not matter what my bank account was, the sort of house I lived in or the type of car I drove... But the world may be different because I did something so bafflingly crazy that it becomes a tourist destination"