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.

3. The replanted irises will grow new roots, so trim back long, trailing roots, leaving enough to help anchor the iris in the soil.

4. Trim the foliage. This will reduce the stress on the growing plant and make it easier for the new plant to stay upright.

After you’re done, what started out like this:

Now looks like this:

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.