They are planted by the thousands all over Japan. In Autumn, pretty much every riverside all over the country will turn red. I post some photos of it every year—it's quite something to see. They are also planted around rice field as a small protection against field mice since they are poisonous. Over 1000 years ago Japan didn't cremate their dead as they do today, so the flower was also planted around cemeteries for the same purpose, to deter pests. Because of that, even today they use the flower in funeral ceremonies and you still seem them dotting cemeteries.