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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.
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.
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.
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.
More articles about dividing and propagating plants
I have a few large areas of irises that I need to divide. Rather than dig up the entire huge clumps, is there a recommended amount I could leave behind while I replant the newly divided rhizomes?
Thank you!
Hi Kim, it may be hard to not dig up the entire clump as they can become entangled. You may want to tackle one big clump at a time, gently disentangle them all and replant some in the original site, and then take the rest to the new area. How many you leave is a matter of aesthetics. 🙂
We are in the process of reorganizing our perennial garden, so I am digging up all the iris and lily bulbs, and will replant them once we refill the garden with new soil. How should I store the bulbs over the next week or two until I can replant them? Thank you
Hi Paula, the first time I divided my irises and didn’t replant them right away, I put them in buckets of water, just around the roots (as per my neighbor’s suggestion). They were fine. Now if I were to do it, I’d probably plant them in soil in buckets until they’re ready to go back in the garden.
Schreiner’s, one of the largest iris growers in the world, warns that iris must not get too much water because it causes rot. So, NEVER put rhizomes in water for more than a few minutes.
I left them in a box in my kitchen for more than a season and they still bloomed once replanted, not the first year though.
Will the rhizomes grow if still have roots but have been hacked apart?
I guess you can plant and see if it comes back!
Do you have a separate bed for your Iris? I have them in with my other flowers and wonder if they are not blooming because the rhizomes are not getting enough sun. Thank you.
I have some in a separate bed and some in a new bed. The ones in the new bed didn’t bloom this year because I divided them last year. Sometimes it takes a year or two for them to rebloom. The garden where I took the divisions was business as usual this spring!
Thank you for posting…this was on my to-do list but thought I had to wait until fall. Now I know!!
I have bearded iris that are in a crowded.container and haven’t bloomed for about 3 yrs. Does it matter what time of year i dig up and divide them since there’s no blooms. Would like to Thin out now.(mid April ).
Thanks so much.
Hi Cory, Mid- to late-summer is best. But if you’re eager to thin sooner, just be sure to wait until the soil warms up. They likely won’t bloom for you this year if you transplant, but you may have luck in the next year or two. 🙂
If you leave the top of the rhizomes out of the soil it helps them bloom. I like to leave some of it exposed so the sun can tell it to bloom. Just my own experience. I love the Iris too! Thanks for your work!
Great, tip, thank you so much!
Should you do this with Siberian irises?
Great question! I don’t grow Siberian irises, but the Canadian Iris Society provides some great tips on dividing here: http://www.cdn-iris.ca/siberian.html
Siberian iris are ready to divide when the center becomes bare. After blooming you can just dig them up shovel deep so you have lots of roots. Then cut them into smaller clumps, replant one in the original hole and now you have enough for all of your friends!!
Thanks so much, Cindy!
What a timely post! I have a huge clump of irises that I haven’t touched in the 9 years we’ve been here so it’s perhaps time that I did something about them 😉 Thanks for the tutorial, Tara!
You’re welcome, Margaret! Happy dividing!
Thank for the picture I’m visual 👍
You’re welcome! Glad it was helpful. 🙂
Same here!
Thank you!
I wish I had seen your post before the last time I divided my white irises! 🤷🏻♀️ I planted them too close together!!! Now, I need to do it again! 😊
Thanks for the great information. I will be supplying lots of neighbors later this summer
Got my dads house, like 2 doz iris, 6 blooms, all grown together, thanks for this info, i am also a visual. 💙
Hello. A nice woman at church just dug up a bunch of her iris plants for me. I’m noticing however that most are roots only without a rhizome. Is it worth planting the ones with roots only?
(This post and these comments have been super helpful!)