Iris are a favorite in the perennial garden, but they can quickly outgrow their space. And when crowded, they won't bloom as well. There are several tips to follow when dividing iris.

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Dividing Iris

The best time to divide an iris is probably during the worst time of the summer months. We want to do it somewhere between mid July and early August. We don’t want to do it in early spring just before they flower just because we don’t want them to lose their blooms. And if we do it just after flowering, the iris is getting ready to go dormant, and a lot of times it won’t rebloom the following year. So by doing it in the summer, when the plant is dormant, we’re more assured to get a better plant and a better return the following year.

With iris, it’s usually better to dig the entire clump. You’ll have a lot of divisions when you’re dividing an iris. Each of the rhizomes will start a new plant. Shake as much of the soil off as possible, so that you can see the roots.

An iris grows with what are called fans. These shoots of green growth that come out are where the new growth is going to come from. All you really need is the rhizome attached to the fan. The rest of it becomes a waste product. We’ll simply break the rhizome off, discard the waste, and you’re ready to replant the iris.

We’re going to make a light hole in the soil, enough so the rhizome is still setting on top, but yet the roots are spread out in the back. Just lightly cover and put the roots in contact with the soil, leaving the rhizome exposed.

It’s best to plant in a fan shape, or circle, with two to three fans. For our next one, we’ll come here, making more of the hole behind the rhizome for the roots to be in contact with the soil. We’ll fill back over the roots, gently press, leaving the rhizome slightly exposed.

Put a third one in to complete the clump. It’s the same thing – we’ll work more on getting the roots spread out, and the roots in contact with the soil, and then press the soil on top.

This is what the plant looks one to two years down the road. You can see how the plant has continued to spread out. You’ve got lots of vigorous buds because we did it at the right time, and they just keep growing out. So it makes a nice clump. In another year, I’ll need to get back in here and divide this plant again to keep it in bounds – keep it in it’s space in the garden, and just to get the maximum amount of flowers.

This feature story prepared with Dennis Patton, Kansas State University Research and Extension Horticulture Agent, Johnson County. For more information, visit your local county extension office or visit our website at

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