The irises have stopped blooming, relegating the bed to foot-tall greenery with their burst of color in May a long lost memory. Now it’s time to divide the plants, but don’t over think the situation. Grab your pitchfork, a sharp knife and a pair of scissors. It also helps to have a trash can nearby, to pick up as you go.

The optimum time to divide iris is after blooming. However it can be done anytime up until the first freeze—you’ll still have blooms next spring. You can also thin, propagate and trade iris throughout the year, as long as you can get your pitchfork in the ground. If you divide in late fall, you may not have blooms the following spring.

Locate the crown of rhizomes. This is the semi-circular formation of the “bulbs” from which iris stalks grow. Dig the pitchfork under the crown and lift out the entire iris plant. Knock off excess dirt exposing the sweet potato-like rhizomes. Cut each rhizome with emerging growth. Examine the fleshy part of the rhizome to make sure it is sturdy—like a raw potato. If it is squishy, holey, discolored or has bugs, throw it in the trash. Continue to cut each rhizome, even if there is no greenery. Also, cut off any brown leaves around the foliage.

Trim the roots to two inches to stimulate growth. If there are no roots or greenery, locate the root buds; these are located on the bottom of the rhizome. Plant the largest rhizome with foliage in the ground from where you took the crown. You may have to back fill some soil into the hole, which makes this the perfect time to add some organic matter like compost or peat moss.

But what about the rhizomes that still need a home? Increase the size of your iris beds or share with friends or neighbors. Or, if it’s a possibility, start a new iris bed on community property in your neighborhood.

Once you have planted your new rhizomes, water thoroughly. Irises are indigenous to this region, love full sun and require very little attention. Also, they thrive in rock gardens. In 2001, I moved to Colorado from Dallas, Texas. Before I left, my Texas neighbor, Iris, gave me her leftover iris rhizomes. I planted the iris before I even unpacked the household goods! They adapted immediately to Colorado’s climate. Fortunately, irises grow well with very little soil amendments and perform in nearly any kind of soil.

Mulching around iris will help hold in moisture and help suppress weeds. If you live on windy sites, consider using mulch that knits together, like pine needles. Or, create a more natural looking landscape by using rock to border the garden.

If you can pick up a pitchfork and wield a paring knife, you can rejuvenate your gardens and make friends with a gift of iris. The best thing is that the iris won’t need dividing for another five years!

For more information on iris, check out PlantTalk #1041 and PlantTalk #1071.

The authors have received training through Colorado State University Cooperative Extension's Master Gardener program and is a Master Gardener volunteer for Larimer County.

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This page updated:  July 24, 2007