Bearded irises put on a floral display in late spring or early summer. By July, after they've bloomed, it may be time to tidy up the clumps, which get congested after four or five years. Dig up and divide their rhizomes, cutting away rot and weak growth and trimming leaves. For optimal growth and display, replant them with the leaves forming the three points of a triangle and the roots pointed toward the center.
Martha Stewart Living, July 2004