Andrew you could ask that question on the "chat" forum, that way Lynn and Twit and Chris, the main "experts" will probably have an answer! I think its totally odd that they have them marked like that, were they from the same growers? (did the labels look the same?) because it could be that different growers label different temps. Personally I'd be surprised if they really can survive at 40 below without snow or some other protection!! One problem in southern areas with regarding these plants is that they can take drought but not full sun, so when deciding where to plant them you should consider this. They like full sun in winter and can take quite a lot of shade in summer. Its funny because even though we're in the same zone, I have a feeling that your temps and humidity are far hotter than mine ever get. These guys prefer cooler temps but can do okay with heat, just shaded.
