It's now clear that the one I tried is from the same source as the ones you are now all trying. They are saying it is incredibly hardy, even to north scandinavia. But mine didn't survive even a mild winter. But I notice on their website they say it may fail due to cold in its first winter, and needs protection for its first winter in the ground. It was not at all a cold winter that year, the one before the recent two cold winters. So be warned to protect it in its first winter - it doesn't take much to kill it in its first winter.