To divide the iris, lift the clump of iris plants out of the ground with a spade or fork. If possible, lift out the mass as a whole. If that is not possible, carefully break the clump into smaller parts and lift them out.
Brush of as much dirt as possible from the iris rhizomes to make it easier to see where to break the clumps apart.
Divide the iris rhizomes into pieces that are 3 to 4 inches long and have at least one fan of leaves on the rhizome. Do not remove the roots from the rhizomes.
Closer to the center of the clump there may be large sections of rhizomes that have no leaf fans. These can be discarded.
Check all of the divided iris rhizomes for iris borers and disease. The iris rhizomes should be firm, not soft. If a rhizome feels soft, throw it away.