Alex, it gets down to -18C here in Nova Scotia, and my two "Cl. New Dawns" do just great, both over 8' high. I had trouble two years ago with one of them when I pruned it, to begin with too heavily, and of course pruned off over half of the following years' growth. I thought I had lost it. I will be very careful ever pruning them again, can bearly get near them anyway! LOL.
