How to divide irises and replant them in the garden

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The front garden of my first home featured huge, gorgeous, tall bearded irises that framed both sides of the front door. The massive blooms were a deep purple hue, and you had to be careful not to brush them with your clothes as you went into the house. Sadly, that house and garden were torn down after we sold, but luckily, I had divided some irises and gifted them to my mom, who in turn gifted some to me once I moved into my current house. These beauties live on in my front garden. Every few years, they need some TLC. This article will explain how to divide irises and replant them in the garden.

Irises have such unique blooms and come in an array of stunning color combinations. Even though they are a rather short-lived bloom, when they do put on their annual show, they add drama to a garden. In my experience, irises are hardy and drought tolerant. However there are pests and diseases to be aware of. This article on cutting back irises explains why you may need to cut back plants before they need to be divided.

How do you know when to divide irises?

Irises need to be divided every three to five years or so. Mid- to late-summer is a good time of year to divide bearded irises. This is a good garden task to do around July or August. You want to make sure that the roots have ample time to grow before winter. You can usually tell that your irises are ready to be divided when a clump looks overgrown, with rhizomes starting to grow into each other and popping up from the soil. This could start to affect bloom production, as well.

knowing when to divide irises — A mess of rhizomes is a clear indication it’s time to divide your irises, especially when they’re pushing each other up and out of the soil!

Dividing irises can improve airflow around each plant. Each plant should have some space to flourish. By dividing large clumps, you can actually get more plants as you separate each rhizome and replant it.

How to divide irises

There are a few tools you’ll need to divide irises. I use a rounded shovel to dig down under the rhizomes. It makes it easy to unearth a whole clump. You can also use a garden fork, but be careful not to split any rhizomes as you dig.

Place the tip of your shovel in the soil a few inches from the clump, dig down, and lift, going all the way around in a circle until you’ve managed to loosen the entire clump. Once you’ve pulled the clump out of the soil, carefully separate the rhizomes.

A sharp knife or hori hori-type garden knife can come in handy for separating rhizomes that are fused together. Do not be afraid to gently cut them apart. Toss away any dead foliage or rhizomes without leaves attached into the compost. Look at your rhizomes and leaves closely for signs of decay or iris borer damage. Soft rot is another disease to look for. Leaves will start to decay and yellow from the leaf tips to the base, resulting in a mushy rhizome.

deep purple iris — My first iris via my first home’s garden, via my mom’s last garden, now in my current garden!

For the rhizomes you decide to keep, cut the leaf fans back so they’re about four to six inches long. This helps the plant focus on growing healthy roots before winter.

Years ago, when I divided my first bunch of irises, I was in the middle of overhauling my whole front yard. Each plant’s rhizomes sat in buckets of water, as recommended by my neighbor (some for a few weeks!), before I was able to replant them. Once nestled safely in their new garden home, the irises all survived the winter.

However you divide your irises, it’s important to note that they may not bloom the year after they’ve been divided or transplanted. But be patient, they should eventually rebloom for you.

Replanting your divided irises

This is a good time to amend the soil, though you want to make sure you don’t add too much nitrogen, as it can cause soft growth and make the plant susceptible to disease.

Irises like sunny spots in the garden that get about six or more hours of sunlight a day. They’re also pretty drought tolerant, so a nice option for sunny areas of the garden. Irises like well-draining soil or heavy soils. And at my local botanical garden, their iris collection is planted in areas of the garden with sandy soils. Though irises enjoy a slightly acidic soil, they thrive in most conditions.

replanting divided irises — I use garden scissors to cut the fan, before replanting my irises.

To plant, dig a shallow hole and create a mound in the middle where the rhizome will sit. Place the rhizome on the mound with the roots in your hole. Cover the roots and then place a thin layer of soil over the rhizome. You want the rhizome itself to be just below soil level, with the top of the rhizome lightly covered in soil. Push any errant roots under the soil with your finger (they tend to pop up sometimes!).

Plant rhizomes about 12 to 24 inches apart. If you plant them closer together, you just may find yourself dividing them sooner, but if you’re okay with that, then plant them as you will!

As the season progresses, the transplanted iris will put down more roots and be settled in its new home for the winter.