Bearded irises are beautiful perennials that bloom in spring, providing a kaleidoscope of delicate, flag-like color. In order for them to continue blooming to their full potential each year, they need to be divided to avoid “choking” themselves out. The bearded iris should be divided in late summer when the weather starts to cool. The following step-by-step guide shows the correct process for dividing these hearty plants for a healthy bloom each spring.
Step 1: Dig around the bearded iris
The bearded iris grows its leaves, flower stems and roots from a thick structure called a rhizome. As a plant matures, the original rhizome produces “baby” rhizomes and eventually dies off, producing less and less blooms.
Carefully dig into the ground around the iris using a garden fork or spade. Take care to avoid chopping into the rhizomes.
Step 2: Pull the rhizomes apart
Pull the rhizomes apart with your hands. Thicker, more stubborn rhizomes may require cutting with a sharp knife. If this is the case, dip the knife in a 10 percent bleach and water solution between cuts. Healthy rhizomes will be about as thick as your thumb, have a good root system, and have one or two leaves. Bigger, older rhizomes with no leaves can be thrown out.
Step 3: Wash the rhizomes off
Gently wash the soil off the rhizomes so you can inspect them for the iris borer (a fat, white worm commonly found in iris beds). If you see any, destroy them immediately and inspect for any signs of rotting. You may also wash the rhizomes in a 10 percent bleach and water solution to help prevent disease, but this will not help rhizomes that already show signs of rotting. Discard any soft, smelly or rotting plants that feel lightweight or hollow.
Step 4: Clip off the leaf blades
To allow the new plant a chance to focus on growing new roots rather than maintaining long leaves, clip off the leaf blades to about four to six inches long. This reduces the stress on the plant as it establishes itself in its new home.
Step 5: Replant the rhizomes
Replant the divisions, placing the rhizomes higher in the holes than the fine roots. Fan the roots out and make sure the top of the rhizome is just visible at the surface of the soil.
Step 6: Keep the distance
Bearded iris plants should be planted about 12 inches apart. If they are of the dwarf variety, plant them a little closer together, or if they are the large variety, plant them further apart. For an eye-pleasing display, position the rhizome so that the fans of leaves all face the same direction. Water your new bearded iris divisions well at planting but do not continue to water unless the weather is dry.
Dividing bearded irises is easy and should be done at the end of each summer to promote a healthy, full bloom in the spring. These perennials thrive especially well in USDA Zones three through nine where temperatures drop below freezing in the winter to allow the plants to go dormant before the next season’s new growth.