Dig a trench and fill it with well-rotted manure, which will feed the ground and hold water. If your soil is heavy, add sharp sand or gravel as well as manure, to improve drainage.
Plant the corms 4in (10cm) apart, 4-6 in (10-15cm) deep. At this depth, the plants are less likely to need staking.
In poor soils, plant five corms in a Gin (15cm) pot. Wait for them to shoot, and plant out in May, when they are established. The plants should flower three months after planting.