To divide iris, dig up the crowded clump using a shovel or garden spade. Gently separate the individual rhizomes by hand, or by using a fork or hand spade. Discard shriveled, hollow, lightweight, or rotten rhizomes, and keep the firm rhizomes with good root fibers and one or two leaf fans attached. Replant the individual rhizomes about 12 inches apart. Plant them shallowly, with root fibers facing down, and splayed apart, with a bit of the top surface of the rhizome visible in the planting hole. If planting in a new area, prepare the bed with soil that drains well.
It’s a good idea to clip the top growth 4 or so inches above the root, so that the individual plants don’t become top heavy, and pull out or tip over during the root re-establishment phase. Cutting back the foliage encourages the plant to send energy to the root system, and discourages overwintering pests and disease.
Water well at planting time, but do not overwater. Rhizomes, like bulbs, are easily susceptible to rot, if the soil is too wet.
Share any extras with neighbors, and friends. Dividing iris is a cost-effective way to spread beauty throughout your garden!