I had one short stem once. I don't know if this applies to amaryllis or not, but with other bulbs, if the dormant period get interrupted by a warm spell, or is too short, that can happen. Not sure if that is what happened to mine or not, I did not pay too much attention. I always compost by coffee grounds, banana peels, and egg shells and add that compost to the soil - they seem to like that.
