Over time, iris become crowded and they stop blooming, so it’s important to dig and divide iris about every 3-4 years in order to reinvigorate the plant.
Iris grow in clumps and the root of an iris is called a rhizome. It is the rhizome that we are going to lift carefully, using a garden fork. You can use a shovel, but be careful to not damage the rhizomes.
Once out of the ground, cut or break apart the rhizomes into sections, with a healthy set of leaves and firm, tan/white roots.
Get rid of rhizomes that are soft, mushy or have holes in them. Holes indicate the presence of iris borers, so you will want to treat the plants you choose to keep, with a garden dust such as Sevin or Eight.
Next, cut the leaves back to about a third of their length.
You are now ready to re-plant. Iris rhizomes grow away from the toe, in the direction of the heel, so keep this in mind as you plant. Iris need well drained soil, so take time to amend your soil with Sheep, Peat and Compost. Add some Bone Meal and place the rhizome in the hole, roots spread out and cover with soil deep enough to just cover the top of the rhizome. Water well and add more soil if necessary. Your iris will establish themselves through the fall and early winter and be ready to bloom for you next spring.