The Homeowners Column

The Homeowners Column

Time to Divide Iris

Photo of Sandra Mason

Sandra Mason
Extension Educator, Horticulture
slmason@illinois.edu

Goddess of the rainbow. Eye of heaven. Fleur-de-lis. Pretty lofty names for a flower, but I think iris can hold up to the expectations. Iris is one of the oldest and most popular perennials. When I see an iris, I always think of my great Aunt Evelyn. As we drove down the driveway to their farm in Indiana, the iris would be an overwhelming eye and nose riot of color and fragrance. Yummm. That one smells good enough to eat. I wonder how long Aunt Evelyn pondered why the damage on her iris looked strangely like teeth marks.

Iris popularity is due to the myriad of flower colors, sizes, flowering times and fragrances. Although many of the over 300 different species of iris are exciting additions to the flower garden, one of the most popular is the bearded or rhizomatous iris.

The iris most people are familiar produces a thick underground stem known as a rhizome. Each rhizome produces a bloom stalk only once with the newly developing rhizomes flowering the next year. There are now reblooming iris available that rebloom in the fall. The rebloomers can be divided in the same way as the one-time bloomers.

The best time to plant or transplant iris is after flowering through August. Iris are one of the few perennials to transplant during the hottest part of the year. Established plantings of iris should be divided every 3-4 years or whenever the clump becomes crowded or when flowering decreases.

To divide iris, carefully lift the old iris rhizome with a spade or spading fork. Shake most of the soil off the roots and set the plants aside on some newspapers. Take a sharp knife and cut the rhizomes apart discarding the center old rhizome. You may still see the old flower stalk on the old rhizome. Be sure the new rhizome has some roots, 3-4 inches of rhizome and a fan of leaves. Cut the fan of leaves back to 6-8 inches tall.

Make sure the new rhizomes feel firm. Soft rhizomes may indicate root rot or iris borers. Any soft rhizomes should be discarded. Do your favorite compression method on any pink caterpillars of the dastardly iris borer found in the rhizome. If you do find iris borer, it is also critical to remove and destroy iris leaves in the fall to remove any overwintering eggs.

Plant the new divisions in a sunny well-drained spot. Dig an ample size hole leaving a ridge of soil down the center of the hole. Place the rhizome over this ridge with the roots spread out on either side. Plant the rhizome so it is about an inch below the soil surface and the plants are about 18-24 inches apart. Firm the soil over the roots and water thoroughly.

U of I Extension Champaign County Master Gardeners Garden Walk was a grand success with over 1,400 people attending. A special thanks to all the garden owners for so graciously opening their gardens to the community. Also a round of applause to the Master Gardeners for working so hard to make the Garden Walk a success. All the proceeds from the garden walk go back into the community through Master Gardener projects at the Champaign County Nursing Home, Humane Society, Juvenile Detention, Centennial High School and the Idea Garden at the U of I Arboretum.

Here are additional communities who could use your support and you can see some great gardens at the same time.

  • Mahomet Garden Walk on Sunday June 24 from 11 am to 5pm. Tickets and maps are available at Mourning Dove Farms.
  • U of I Extension Vermilion County Master Gardeners Garden Walk Sunday June 24 from 12-5 in Danville. Contact U of I Extension Vermilion County (217) 442-8615.

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