Q. Please advise on the correct time and procedure for dividing iris.
A. If you want to divide bearded iris, do so after it flowers, but before August. With a sharp, sterilized knife, cut the rhizome into pieces containing a set of leaves and healthy roots. Plant the pieces 1 inch deep, and cut the foliage down to a 6-inch fan that faces away from the planting circle. Siberian iris (I. sibirica) can be divided in July by digging up the entire clump with a sharp shovel and then separating the clump into as many sections as you want. For an established clump, this might require a pruning saw. Replant the sections in full sun at the same planting depth as the original clump. Early or spring-flowering little irises (I. danfordiae, I. reticulata) can be lifted, separated and replanted in fall, although this is often not necessary since they tend to naturalize by themselves.