Answer: Perennial iris such as Siberian iris (Iris sibirica) and the bearded iris (such as Iris germanica) are left in place year round so you would not need to dig and replant them. Siberian iris can be left undisturbed for a number of years, however if you need to divide a clump it is best done in the fall. The bearded iris tend to become crowded after three to five years and will need periodic division. This is done in late summer. If you have a bulb type of iris such as Iris reticulata, these would be left in place in the ground from year to year. I hope this answers your question.
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