Bearded Irises are tall, lovely perennials that grow from rhizomes. They are hardy in zones 3 to 10 and require full sun. These plants need to be divided every three to four years so they don't get overcrowded which decreases flowering.
Irises should be divided in July or August when they are no longer flowering. With a spade, carefully dig out a clump of the root-like rhizomes.
Clear off the dirt and snip the leaves to about 6 inches with garden snips or shears.
With a knife, cut the rhizomes apart so you have one fan of leaves, a healthy section of the rhizome and good-looking roots. Discard any dead or diseased portions of the rhizomes.
Dig a new hole with the spade large enough for the rhizome and its roots. Create a mound of dirt in the middle and place the rhizome clump on top, spreading the roots into the hole. Cover the rhizome with soil. The rhizome should be just barely under the surface of the soil.
Space the divisions 1 to 2 feet apart. Groupings of three or four plants are ideal. After planting, water generously.