Garfield County Cooperative Extension

It’s Time to Divide Iris

Rick Nelson Extension Educator, Ag/4-H

August is typically hot and dry. However this year we have experienced a timely rain shower or two. The next few weeks will provide the best opportunity 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 southern high plains. Many plants have been passed along to family members, creating legacies. Iris bloom late April through May are dormant during the summer months. Once fall arrives, irises experience rapid growth underground in the rhizomes, setting their flower buds for the following spring. This is what makes now the ideal time to divide iris.

As a general rule, divide iris every three to five years. Without timely division, the plants outgrow their allotted space and the bloom quality of the iris clump is greatly diminished. 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. Iris usually have a fairly shallow root system so deep digging will not be necessary. The recent rains may have made it easier to dig and prepare soil.

Once out of the ground, clean the soil from the roots and break apart the rhizomes. A gardener 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 to one half at this time to make the plant more manageable.

Now that the hard part is complete, replanting iris rhizome is simple. Prepare the soil by spading and incorporating an ample supply of compost or perhaps peat moss actually anything to increase the organic matter which will assist in the in the breakup of the hard clay soils encountered in our area.

Plant iris rhizomes in shallow soil. Cover only the bottom half of the rhizome leaving the top half exposed to the sun.  Planting to deeply may decrease flowering the following spring. 

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 planting process is done. Water as needed heading into winter to ensure survival and increase the likelihood of strong flowering in the spring.

After dividing the iris, set back and enjoy your reward of iris blooming the next May.  After all this is one of the easiest perennials to grow.                                                                                                      

 For those wanting to plant their first iris bed this fall, the North Central Iris Society will offer a variety of locally grown rhizomes for sale in September.





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