I've grown this plant for about 10 years in Switzerland and now 10 years in the Pacific Northwest. They do like moist but not necessarily...Read More wet or boggy conditions. Once establishes they will be just fine in average soil, preferably fertile. As far as hardiness I'd put them at least to USDA zone 5 or colder.
They can bloom as early as 6 years after sowing and will bloom the following year again if dead headed in time.
Eventually they'll grow into multiple stem clumps, very impressive.
I've grown this plant for about 10 years in Switzerland and now 10 years in the Pacific Northwest. They do like moist but not necessarily...Read More