How to Divide Bearded Irises

by Daisy on 09/19/2013

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One of the many benefits of volunteering is learning new things.

I volunteered at the Memphis Botanic Gardens Iris Garden this summer and took away more than I contributed. Learning to divide and replant bearded irises has been on my list for a long time and I had a lesson from Carmen Cooley, President of the Memphis Iris Society.  Ever since this lesson, every time I pass a crowded clump of irises in someone’s yard I have an urge to get in there and work on it.

I want to sneak into the yards at night, dressed in black, and quietly and carefully dig, cull, trim, and replant their rhizomes.

I’ll need some sort of badge in case I’m caught in the act.  Iris Warden? Iris Ranger?

It would be a pretty badge, with an iris in the middle.

Ahem.

Moving along, here are some things to consider when renovating an old iris bed.

  • The best time to divide bearded irises is in the late summer/early fall.
  • At least a half a day of sun is required, in a well-drained spot. Bearded irises hate soggy soil. A bit dry is okay as they are very drought tolerant. Irises are long-lived and conditions change over time. I had some irises in my yard that may have had enough sun when they were planted during the Roosevelt Administration, but which were in complete shade by the time I relocated them.
  • Neutral to slightly acid soil pH, around 6.8-7.0.  It’s best amended in the spring with bone meal or rock phosphate and again in the late summer or fall when you divide your irises (every 3-4 years). If a fertilizer is used, use one for bulbs with low nitrogen; high nitrogen may encourage rot and too much (but weak) foliar growth.

Here’s how to dig up and replant bearded irises:

1. Using a garden fork (preferred) or spade, dig carefully around the clump to raise the rhizomes and their roots out of the soil.  Tease and/or break the rhizomes apart with your hands or a hand cultivator if they are tightly clustered. Truly matted clumps may take more bullying than you think, so use as much muscle as you need to separate them. They’re surprisingly tough.

2. Shake off the dirt from the roots so you can examine the rhizomes. Discard any that are mushy, smelly, rootless, or dry and practically weightless. If a portion of the rhizome is dead and rootless, cut this off. Disinfect your knife or secateur between cuts with a 10% bleach solution to avoid spreading disease between plants. Some gardeners recommend a sprinkle of Comet (a disinfectant scouring powder) on cuts to keep disease at bay. Below you can see the some iris borer damage.

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3. The replanted irises will grow new roots, so trim back long, trailing roots, leaving enough to help anchor the iris in the soil.
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4. Trim the foliage. This will reduce the stress on the growing plant and make it easier for the new plant to stay upright.
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After you’re done, what started out like this:

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Now looks like this:

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It will almost make you forget your house is a wreck and you have fourteen loads of laundry to do.

Next I’ll post about how to replant the rhizomes.



{ 7 comments… read them below or add one }

Sarit September 19, 2013 at 8:28 am

Very nice article. I’m looking forward to the next part

Debbie September 21, 2013 at 5:28 am

Excellent information. We’re having a very rainy weekend here in NW Florida, so I’m going to repot my lavender & try to get my winter garden prepped. Your pictures are very nice & you’re inspiring me to get out in my garden.

Thanks & have a terrific day!

Debbie…(0;
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Cynthia C September 25, 2013 at 7:16 am

Thank you for the information! I have a beautiful bed of iris that have never bloomed until this year – I have divided before, but I think I planted them too deep. Your blog on planting was also helpful – Thank you – I LOVE iris, Think I’ll get busy on separating and replanting this weekened!

Daisy September 25, 2013 at 11:26 am

Cynthia C–You’re welcome, Cynthia. I never knew why my irises wouldn’t bloom, but I have high hopes for next year now that they are getting the right treatment. They are gorgeous, aren’t they?

Belinda January 24, 2014 at 11:40 pm

Very good info on the iris…now, let me tell you about all the plants I’ve been gifted with…lol. I have several lovely clumps—growing right where I left the grocery bag laying when I brought them home. I have moved a few of them to more ideal locations when they blossom so that I know what color they are…..

Daisy Debs June 28, 2014 at 6:46 am

You can be an Iris Ranger …….and I would like to be a Greenhouse Inspector . If there is one thing I cant stand , its seeing a neglected and empty greenhouse ! If you,ve got a greenhouse …then USE IT …or I will come and get you all !
I too would like a badge…… : )

Daisy June 28, 2014 at 1:38 pm

Daisy Debs–No doubt. At least let someone else use it!

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