KC Gardens

Now is the time to divide your iris plants, after the rain. Here’s how to do it right

Now is the perfect time to divide your irises as the soil has been loosened by recent rains. Irises are one of the easiest perennials to grow in our area.
Now is the perfect time to divide your irises as the soil has been loosened by recent rains. Irises are one of the easiest perennials to grow in our area. Johnson County K-State Research & Extension

Early August is typically hot and dry. However, this year we have had a reprieve with cooler temperatures and timely rainfall.

The next few weeks is the best time in recent years to get in the garden and divide any overgrown clumps of iris.

Iris is one of the easiest to grow garden perennials. Tall bearded iris grace gardens across the metro. Many plants are passed along to family members, creating legacies.

Irises, which bloom late-April through mid-May, are dormant during summer months. Once fall arrives, irises experience rapid growth underground in the rhizome, setting their flower buds for the following spring. That is why this is the ideal time to divide.

As a general rule, divide iris about every three to five years. Without timely dividing, the plants outgrow their allotted space and the bloom quality of the clump decreases.

By dividing now, spring flowers are more dependable.

There is no simple way to approach a clump of overgrown iris but to just jump in and tackle it.

Start by digging up the entire clump. They have a fairly shallow root system so deep digging is not needed. The recent rains make it easier to dig and prepare the soil.

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

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

Now that the hard part is 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.

Plant iris rhizomes in shallow soil. Cover only the bottom half of the rhizome leaving the top exposed to the sun. Planting too deeply decreases flowering.

A nice size division or start is a grouping of three prepared rhizomes. Point the leaves outward in a circle and cover lightly with soil. Thoroughly water and the process is done. Water as needed heading into winter to ensure survival and increase the likelihood of strong flowers.

Mother Nature has graced us with almost perfect weather conditions, so do not miss your opportunity to tackle an overgrown planting.

After dividing the iris, sit back and enjoy your reward of iris blossoms next May. It is one of the easiest perennials to grow in our area.

Dennis Patton is a horticulture agent with Kansas State University Research and Extension. Got a question for him or other university extension experts? Email them to garden.help@jocogov.org.

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