Some species and hybrids can spread rhizomatously rather vigorously :-) But I'd consider that to be a plus. I attempted several of the Asian species in my previous Shoreline garden but they never thrived and eventually petered out. Guess the conditions were not quite right even though it was a semi-shady site with excellent, organically rich and well drained soil that stayed nicely moist.

Far Reaches carries some of the best selections available. Whichever it is, I'm sure it's a stunner!

Yes, let them spread! Last year it had one purple flower that you had to get on your knees to see. it formed a fruit that I collected and when it had dried, I opened it up in hopes of collecting seeds. It was as empty as Al Capones vault. :o(. Maybe this year.