Dividing and replanting iris will enhance flower production

Irises are relatively carefree, easy to grow and long-lived perennials, said David Hillock, Oklahoma State University Cooperative Extension consumer horticulturist.

“When they are well cared for, they need to be divided about every three to four years,” Hillock said. “Crowded iris will begin to decline growth and will have fewer, as well as smaller, flowers.” 

Another sign your iris should be divided and transplanted is if the rhizomes start heaving out of the ground. Overcrowded iris rhizomes will start to push on each other, which results in the entire root system literally pushing out of the ground. Iris roots may looks like a big pile of spaghetti when they need to be divided.

Now through the end of August is the optimal time in Oklahoma to divide and replant your iris. Hillock suggests starting by lifting the clump of iris plants out of the ground with a spade or garden fork.

“Be sure to remove any segments that are diseased, riddled with insects and that are small and weak,” he said. “Separate healthy rhizomes into segments with one fan of leaves and several roots. Cut the leaves back to about 6 inches, as this will allow the plant to re-establish its roots without having to support a large amount of foliage at the same time.”

Once the iris rhizomes have been divided, they can be replanted. When planting the new plant, spread the roots out in the soil and position the top of the rhizome at the soil surface. If planted too deep they will not flower as well and are more susceptible to disease and insect attack. Also, if planting several iris near each other, point the rhizomes away from each other and space the new plantings about 18 inches apart.

“Spread out the roots around the rhizome and then cover the roots and the rhizome with dirt. Be sure to thoroughly water in the newly transplanted iris plants. Now they are ready for the fall/winter season and should produce more flowers for you next year,” Hillock said.

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Trisha Gedon
Communications Specialist
Agricultural Communications Services
Oklahoma State University
136 Agriculture North
Stillwater, OK  74078
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