The best time to plant most varieties of iris is usually September. The best way is to plant as a rhizome, just below the surface of the soil. They can be grown from seed but they may take a few years to flower. They like full sun or partial shade, and the soil conditions should be moist but well drained, although some varieties like conditions so moist that they will grow in a container of water.
Irises need watering well through the dry weather, especially when they are still establishing and will benefit from a slow-release fertiliser too. To create a bigger display or stop them looking congested you can divide the rhizomes of the Iris. About 6 weeks after the flowering season cut the leaves down to about 15 cm, dig up the rhizome and pull or cut apart the fans and re-plant at least 12cm apart.