Iris Care and Dividing
Irises can become congested over time, which tends to inhibit flowering. Remedy this by lifting and dividing their rhizomes to give them a little more space. Heres how:
Use a fork to dig up a clump of irises. Ease the plants from the soil, trying not to spear any of the rhizomes.
Pull the congested rhizomes apart by hand, or cut them with a knife. Choose healthy pieces with leaves and discard old, woody sections.
Check for iris borer and soft rot now. Iris borer is a caterpillar that hatches in the spring from eggs that are deposited on old leaves of iris. They climb up the leaves and prick a hole into the leaf and eat or tunnel their way to the rhizomes. In the fall they leave the rhizomes when they are 1 1/2 to 2 inches long, going into the soil, where they pupate in the spring as moths. The best thing to prevent iris borer is to remove all old leaves in the fall and destroy them. Any tunneling seen on leaves in the spring should be squashed between your fingers to help kill the little caterpillars.
Soft rot is a bacterial rot of the rhizome, which can be caused by iris borers or by over watering. The rhizome is mushy and smells really bad. If you find soft rot, cut away any bad part of the rhizome. Soak the rhizome in a 10% bleach solution (1 part bleach to 9 parts water) for 1 to 10 minutes. Allow to air dry over night before replanting.
Newly planted rhizomes are vulnerable to being knocked down by the wind. Cut the leaves back to half into a fan shape or inverted V. This helps also because the roots have been disturbed and need to reestablish themselves before being able to supply all the water that a full sized iris would need.
Replant healthy rhizomes about 12 inches apart in fertile soil.
Remember to plant only the top half of the rhizome. Iris like their rhizomes to be on top of the soil.
This process is best repeated every three years or so.
