I have to admit that I have a clump that has defied all rationality. It has grown in a damp spot on the west side of a garage under a medlar tree. So it gets very little direct sun. There are large beech trees overhead and I leave all the beech leaves in place as well. I planted the bulbs first then forgetting where the bulbs were planted the medlar. They have flowered reliably for twelve years and have increased nicely. Can't tell you all why but they come back as reliable as April 15 ( tax due day here in the US). Arnold