Iris should be divided about every three to five years. Adele Wilcoxen Special to The Star
Iris should be divided about every three to five years. Adele Wilcoxen Special to The Star

KC Gardens

Answering your gardening questions from asters to zoysia

KC Gardens

Time to divide the iris


Special to The Star

August 04, 2017 07:00 AM

Iris are one of the easiest garden flowers to grow. They are also referred to as a pass-along plant, because we have starts from our parents or grandparents that have been handed down through generations. This perennial favorite provides years of pleasure with minimal care. But periodic dividing is important for maintaining plant health.

Late July through early August is the best time to divide iris, as they are dormant during the summer. They then put on a flush of growth in preparation for winter. This dormant period makes it the ideal time to renovate a clump.

Iris, as a general rule, should be divided about every three to five years. Without timely dividing, the plants simply outgrow their allotted space in the garden. The bloom quality of the clump also decreases when plants become overcrowded.

There is no simple way to approach a clump of overgrown iris. Start by digging the entire clump. The plants have a fairly shallow root system, so deep digging is not needed, and the recent rains will make it much easier to dig and prepare the soil.

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Once they are out of the ground, start breaking the plants apart. Iris rhizomes are vigorous and almost indestructible. Knock the soil off the roots, then break and pull the rhizomes apart. You will end up with more divisions than anyone could possibly use, so discard small roots.

Iris rhizomes grow outward. The old rhizome farthest away from the fan of leaves can be discarded. All that is needed is the rhizome or last knee or bump attached to the leaves. Many prefer to cut the leaves back by one half to make the plant more manageable.

The hard part is now done; replanting the iris rhizomes is easy. Prepare the soil by spading and working in an ample supply of compost or peat moss to help break up the hard clay soils commonly found in our area. You are now ready for planting.

Iris rhizomes should be planted shallow. Cover only the bottom half of the rhizome and leave the top exposed to the sun. A nice size division or start is a grouping of about three prepared rhizomes. Point the leaves outward in a circle and cover lightly. Thoroughly water them in and the process is done.

Sit back and wait till next May for a wonderful reward of iris blossoms. Enjoy one of KC’s easiest-to-grow perennials, as there is nothing finer than a graceful iris blossom.

For more information on dividing iris, watch a short video produced by K-State Research and Extension at