You can divide an iris any time after blooming is completed. But, for best results, divide the plant in late summer and early fall. Fall is the best time to plant the rhizomes to allow for adequate root growth and establishment before winter. During late summer, the buds for next year’s blooms are formed.

Before dividing an iris, cut the leaves to about one-third their full height. Dig up the entire clump of rhizomes. It may be necessary to wash away some soil to see just how the rhizomes look. The most vigorous rhizomes will be those on the outer sides of the clump. Carefully cut the clump apart, saving the vigorous ones and discarding the inner, leafless ones. Be sure the new rhizome has some roots, 3-4 inches of rhizome, and a fan of leaves. When separated from the clump, each division is ready to plant.

For maximum display of flowers, irises need to be dug and divided every three to four years. If iris plants have not flowered well, look for a new location during renovation.