I adore alliums and have quite a few varieties. One variety of the big ones (Ambassador) failed to return, but my supplier suggested planting them quite deep (4 times the depth of the bulb). I tried that and they have returned for the last 3 years, although I don't actually know that the reason they regrow is the deeper planting. Purple Sensation seems indestructible here, keeps seeding itself all over to the point where it's almost attained weed status.
