This is amaranthus - specifically, "love lies bleeding." What a horrible name! I ordered a packet of amaranthus seeds a few years ago and there will never be a need to plant it again. It re-seeds liberally, lots of "weeding" the seedlings. I grow this for the birds - they eat the seeds right off the plant through the winter - and for a friend who uses the spectacular flower sprays for dried flower arrangements. This plant does require staking towards the end of the season. I've read in some countries, this is treated like a grain.