A friend in Hay River Northwest Territories is growing this for some years, and says its on the verge of weed status!! Such a weed I could use...
Wow! Is that midnight sun the secret? :o ???
I dunno--he does grow some pretty impressive stuff up there in zone 1--tons of species lilies, for example..
he does have- long summer days, as you mention,
-a fairly warm summer, at least in recent years, its often warmer than ours here next to the foothills!
-deep persistent snow cover for those plants that may be partial to that!