lilylu, if you put them up against a structure, like your house, you can create a "micro
zone" that will be warmer, and then if you mulch them, or cover them with plastic and straw, you can probably overwinter them there.
i was going to say (but was at work and not supposed to be posting) i had mine in a bed that was north east facing, and they bloomed great. i didn't do anything to them and they came back year after year. of course, i am in a warmer spot than you, but...
with a carefully planned (or happily accidental) micro climate, you can gain 2 or 3
zones sometimes.