How to Divide Bearded Irises
Division is the easiest method of making new plants.
Step 1: Split and Trim
Split the rhizomes into sections, so that each has healthy shoots and good roots. Trim off the older sections farthest from the leaves with a knife, and dust cut surfaces with fungicide.
Step 2: Cut Back Leaves
Trim long roots back by one-third, and cut leaves to about 6 in (15 cm). This will reduce rocking by the wind, keeping the replanted section stable until it develops strong, anchoring roots. Replant the sections at the same depth as before in well-prepared ground, spaced about 5 in (12 cm) apart. Firm in, level, and water well.