KUSA - Bearded iris are so easy to grow that we often neglect them. That's fine, they thrive on neglect. At some point, however, they need to be dug up, divided and re-planted. There's no strict rule as to how often this should be done, but after more than five years they start to decline and bloom less or not at all.
Early summer is the optimum time to divide iris, although it can be done at most any time of year. They have the entire summer and fall to settle in and put out new growth.
To start, lift the entire clump with a spade or digging fork. Pull the clumps apart into single "fans" of leaves. Discard the old, pithy, dried up parts of the rhizomes.
Trim the foliage back by half with scissors. This allows the roots to do their work of settling in without trying to support all that top growth. This is the only time iris leaves should be trimmed back. Never cut the foliage back unless you are transplanting them since this inhibits the plants' ability to renew themselves for the next year.
Work compost into the soil and replant the rhizomes about an inch deep and keep them moist for several weeks. You'll have plenty of extras to plant in other parts of your garden or to share with friends and family.
Bearded iris thrive in sunny conditions and are very drought tolerant once established. It will take the replanted iris a year or two to get back up to full speed. After that, you can go back to neglecting them.
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