DIVIDING OLD IRIS CLUMPS

Although your iris bloom should be fairly good the year after transplanting, your best bloom will occur in the second to fourth years, so do not divide your clumps too soon. However, after three to four years the rhizomes will become crowded and should be dug, divided and replanted. This is also the time to revitalize your soil by adding humus and fertilizer as recommended for new plants. Dig up the clump and remove and discard the old, bare center rhizomes. Cut the foliage back into an inverted V about 4 to 5 inches above the rhizome. Then replant the best of the remaining rhizomes. If Iris are allowed to become too overcrowded the bloom will suffer, some varieties may crowd others out and disease problems may be aggravated. Excess rhizomes make wonderful gifts for family and friends.. The closer the rhizomes are planted together the sooner you will have to divide them.
There will be 3 or more increases each year from each “mother” rhizome. It is recommended that the mother rhizome be removed from the new increases as-soon-as they are old enough to develop on their own. Use a sharp knife to lift the mother rhizome and out of the clump. This separation should be done every year to help prevent soft rot.