Bill,
I'm in zone 3 and my one Doyle Blackberry did survive its first Winter
here. It produced a few berries in its first season but most new
transplants tend to try to produce too late in the season for the fruit to
ripen. If it survives its second Winter here, I'll expect ripe fruit to
come from it. BTW, I didn't give that Doyle plant any protection other than
snow cover.