How to Separate and Thin Irises

Cut the leaves straight across the top with a pair of sharp shears. Make the cut 1/2 to 2/3 from the top of the leaves.

Place a garden fork on the soil 2 to 3 inches from the base of the plant, and press the fork down into the soil. Pull back on the fork to lift the rhizomes out of the soil.

Brush off as much of the dirt as possible from the iris rhizomes. Rinse off the rest of the soil with water.

Divide the rhizomes into sections by pulling them apart with your fingers or cutting them with a knife. Divide irises so that each root section has a set of leaves.

Feel the rhizome sections for soft spots. Soft, mushy areas indicate an infestation of iris borer or bacterial soft rot. Cut away and discard diseased roots.

Replant the irises in a sunny spot with loamy soil and good drainage. Space the plants 18 to 24 inches apart in groups of three to seven.

Dig a hole slightly longer than the rhizome, leaving a small mound in the center of the hole. Place the rhizome on top of the mound, with the long roots hanging down the side. Make the hole shallow, so the top of the rhizome is covered with only 1/4 inch of soil.

Replace the soil around the roots. Water the new transplants. Mulch newly planted irises with a 2- to 4-inch layer of straw for the first winter in cold climates.