Answer: The typical first frost date in your area is the end of September, so you should divide and replant your iris as soon as possible, so they'll have a chance to settle in before winter comes. Carefully dig the rhizomes out, cut or break off the ends to replant, and discard the old centers. Cut the foliage and the roots back to about six inches. Then amend the bed with plenty of organic matter and place the tops of the rhizomes so they're just a the soil surface. Water them in well. To help keep weeds down, lay 3-4 inches of mulch over the top of the soil surface.
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