Iris planted in the spring should have their roots fanned out around the sides of the mound. The rhizome itself should sit at about ground level. Growers differ as to whether it is best to cover the rhizome completely with a light layer of soil or to leave the tops a bit exposed. For the weekend gardener, soaker hoses make watering irises a breeze, providing deep watering slowly when they dry out. In Southern California I water once every week to ten days.
Irises multiply out from the center, which over time, becomes dry and dead.
Every three to four years, they need to be dug up, divided into new plants and replanted to provide the most flowers. May. Cut off dead blossoms and dead bloom stalks when the iris has stopped blossoming, but don't cut back the leaves until they begin to turn brown in the fall. The leaves are needed to produce next year's blooms. When you do cut, leave a fan shape about six inches long. Feed your irises a teaspoon of bone meal every fall and when you replant.