July's the perfect time to do it for a glorious display of blooms next summer.
Bearded iris make a lovely display in the garden in June with their attractive flowers on tall stems. They thrive in a well-drained soil and sunny position so that the sun can bake the exposed rhizomes. This is essential to promote flowering the following summer. After being planted in the same spot for a few years the thick, fleshy rhizomes can become over-crowed and very often the oldest parts in the centre of the clump dies out. This often coincides with a lack of flowers. As soon as this happens you need to dig up the clump, divide and replant the outer, healthy rhizomes to rejuvenate the clump. Most perennial plants are divided in the dormant season, but bearded iris is done now, in July. The plants don’t mind being disturbed in the middle of the summer, in fact it’s the ideal time because bearded iris naturally has a growth spurt in late summer and produces new roots and foliage. When dividing, you can replant in the same position as long as you fork over the soil and add a little organic matter. If planting some of the divisions elsewhere in the garden, remember that it needs to be a sunny position that isn’t shadowed by any overhanging trees and shrubs. Done now you should get a glorious display next June.