You all posted online that now was the time to divide and replant crowded iris. How do I do that? RW

The first exposure to iris for a lot of us was likely in our grandparent’s garden. They seem like kind of an old school flower, but sometimes old school is the best school.

The name for iris traces back to Greek mythology where the goddess Iris was the goddess of rainbows. She was apparently the messenger for the gods as she brought messaged from the gods to the humans below.

As a flower, iris are a stable, easy to grow flower that has some built in drought tolerance. And, if you are in an area where you have issues with deer eating your plants, deer don’t really like iris.

It’s common for iris to stop blooming and bloom less if they become too crowded. Iris grow from a rootlike structure known as a rhizome. These rhizomes grow horizontally underground and serve as the place where nutrients are stored for the plant. As these rhizomes grow from season to season, they can become overcrowded which causes the plants to suffer due to competition for resources. When they don’t get the nutrients they need, blooms get scarce.

To prevent overcrowding, you should plan on thinning your iris every 3 to 5 years. Thinning is a great way to move iris to other parts of your garden or share them with friends. Late summer is a good time to thin your iris.

To thin, start by cutting the leaf blades down to about 4 to 6 inches in length. This will help the plant focus its energy on developing a new root system rather than trying to support the top growth.

After trimming the leaves, dig the rhizomes up. Be careful digging because you don’t want to damage the rhizomes. Try digging at the outside edges of the plant and then lifting them up with a spade or garden fork. Once they are out of the ground, begin separating the rhizomes from one another. This should be easily accomplished by hand. For replanting, you want good, healthy rhizomes that are about as thick as your thumb and have one of two leaf blades attached. If there are large ones or some with no leaves, or if any of them are squishy, just discard them.

As far as relocation goes, iris like a location that gets full sun and that drains well. Typically, we recommend adding mulch when planting something, but this is not true for iris. Mulch will help hold moisture which can contribute to fungal disease in iris.

Iris have shallow roots so you only need to dig down about 4 to 5 inches when replanting. Make sure the roots are all underground but let the top of the rhizome have a slight exposure to air. With iris, it’s better to plant them too shallow rather than too deep. After planting, give them a good soaking with the hose and that’s all there is to it. Good luck.

You can get answers to all your gardening questions by calling the Tulsa Master Gardeners Help Line at 918-746-3701 or by emailing us at mg@tulsamastergardeners.org. Photo: 

John Ruter, University of Georgia, Bugwood.org