A few cultivars actually bloom again in late summer or early fall. Gardeners can choose from several thousand named varieties. If not divided, the plants become overcrowded and flower production decreases. Crowded plants also are more prone to disease problems. The best time to dig, divide and transplant bearded irises is in July and August.
Irises grow from thick, fleshy, underground stems called rhizomes.
Carefully dig up the iris clumps with a spade. Cut the leaves back to one-third their original height. Wash the soil from the rhizomes with a stream of water. Then cut the rhizomes apart with a sharp knife. Each division should have a fan of leaves, a healthy rhizome and several large roots.