Many of my iris didn’t bloom this year. Was it the heat or something else? CR

Iris have an interesting origin story. Their name traces back to Greek mythology where the goddess Iris was the goddess of rainbows. According to the mythology, she also served as a messenger for the gods as she brought messages from them to humans. Iris was also referenced in Homer’s Iliad.

As a flower, iris are pretty easy to grow and somewhat drought tolerant. Plus, if you have a problem with deer eating your plants, deer don’t seem to like iris very much.

When iris plants stop blooming or are not as robust in their blooms, overcrowding is likely the cause. Iris have a rootlike structure called rhizomes that grow horizontally underground. These rhizomes collect and store food for the plant. As the plants expand and develop other rhizomes, they can get overcrowded which causes the plants to suffer as they compete for resources. Without adequate resources, they don’t bloom as much.

To prevent this overcrowding, iris need to be thinned every 3 to 5 years. Thinning is a great way to relocate iris rhizomes to other parts of your garden or to share them with friends and neighbors. Late summer is a good time to thin out your iris.

To thin, start by cutting back the leaf blades to about 4 to 6 inches in length. Doing this will help the plants develop a new root system faster. Once you have the leaf blades trimmed, you can dig them up using a garden fork or spade. Be sure to dig outside of the iris clump to start so you don’t accidentally end up cutting some of your iris rhizomes.

Once you get these rhizomes out of the ground, you can divide the clumps by pulling them apart. Breaking them apart is not difficult and should easily be accomplished by hand. You’re looking for good healthy rhizomes.

Healthy rhizomes should be about as thick as your thumb, have one or two leaf blades attached, and some small roots. If you have some large ones without any leaves, you can just discard them. Also, if any of them feel squishy, discard them as well.

If you are going to relocate some of your iris rhizomes, remember to plant them in a place that gets full sun in soil that drains well. Now I know we talk about mulch being a great addition to your garden, but this doesn’t hold true for iris. With iris, the moisture that mulch helps retain can contribute to fungal disease, so no mulch on the iris.

Since these plants have shallow roots, you will only need to dig down about 4 or 5 inches when replanting. Make sure the roots are below the surface but leave the rhizome just barely exposed to the air. With iris, it’s better to be too shallow than too deep.

Once replanted, give them a good watering, and enjoy the rest of your day. 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