They bloom from late spring to early summer. I lived in Connecticut at the time when we had one, but they are native to eastern Asia from Siberia south to Japan. It's perennial so it will die back in the autumn and winter, but they usually come back in spring. So if you are still living in Japan, it should do well there since it is a native plant.
Hmmmmmm, I haven't seen it growing wild. But, I live in a city-like area...so... (yes, I'm in Japan for at least another year and a half. ) Thank you for sharing your knowledge!
But I met a monk at a local temple who told me about it in Japanese-- maybe he knows where some are on display in a local garden. I'm not sure i could take care of one-- I have this tiny little plot of earth, and I can barely be bothered to weed it. *grins* I like art more than weeding.