Although irises are easy-care plants that require little maintenance once they're established, the plant should be split every three to five years to keep it vigorous and blooming its beautiful best. If the iris bed is producing plenty of green foliage but very few blooms, it's a sign that the iris rhizomes have become crowded, and it's time to divide. Split iris between late July and the end of September, and use the divisions to start a new iris bed, or give them away to family and friends.
Use a clean pair of scissors to trim the iris leaves down to about a third of their height.
Insert a garden fork or a straight-edge shovel near the iris plant, and lift the clump carefully out of the soil. Inspect the rhizomes, and discard the old rhizomes in the middle of the clump, along with any that appear soft, spongy or diseased or don't have leaf fans.
Clean the iris rhizomes with a clean, sharp knife. Each rhizome to be transplanted needs to have a healthy root system and at least one fan of leaves.
Dig a hole for each newly divided rhizome, with the top of the rhizome just barely visible above the top of the soil. Pack the soil down firmly with your foot, and water the soil until it's damp, but not soaked. Iris appreciates soil on the dry side, and will rot in soil that's too wet. The newly-transplanted iris may not bloom much the first year, but will be back to normal by the second and third years.