If your irises aren’t giving you that vibrant spring flush of color like they used to, it might be time to give them a bit more breathing room.
Irises are generally easy to grow, long-lived, and relatively carefree. However, overcrowding can sneak up on you, leading to fewer of those stunning spring blooms we all look forward to—especially with varieties like Siberian and Japanese irises, which spread through rhizomes and really thrive when they have some space to stretch out.
Dividing them every three to five years can make a huge difference in their overall health and the number of blooms they produce. Plus, splitting up your irises doesn’t just help with flowering—it also helps fend off problems like iris borers and soft rot.
The great news? Dividing irises is easier than you might think.
Now, you might be wondering, “Okay, but when’s the best time to do this, and how do I go about it?” Don’t worry, I’ve got you covered. Timing is everything—late summer to early fall is your sweet spot—and there are a few simple steps to make sure your irises come back stronger and more vibrant than ever.
Why Divide Irises?
The flowering season of the bearded iris is a key moment in the garden, usually kicking off just before the roses start to bloom.
These irises grow from rhizomes, which are thick, root-like structures that spread out horizontally just beneath the soil. Over time, new rhizomes sprout from the old ones, leading to fresh growth and beautiful flowers.
However, after a few years, the central rhizome starts to age and produce fewer blooms, leaving a gap in the garden bed where the original plant used to be. Meanwhile, the younger, healthier plants begin to form a ring around this empty spot.
When this happens, it’s important to divide the rhizomes. If you don’t, the gap in the middle will keep getting bigger, with the flowers only blooming around the edges. By dividing the rhizomes, you give the plant a chance to rejuvenate, helping it continue to thrive and keeping your garden looking its best.
When to Divide and Transplant Bearded Iris?
To ensure a spectacular spring show next year, plan on dividing your irises about six to eight weeks after they finish blooming—just after the worst of the summer heat has passed. This allows your irises to gather energy and settle into their new spots, ready to burst into bloom next season.
If your irises bloom in late spring, the best time of year to divide your bearded irises is mid- to late-summer, usually between July and September, depending on where you live. For most areas in the U.S., late July through mid-August is the sweet spot. This timing gives your irises the perfect window to settle into their new spots before cooler temperatures set in.
How to Divide and Replant the Rhizomes of the Bearded Iris
1: Gathering Your Tools
Before you start dividing your irises, it’s essential to gather all the tools you’ll need. Having everything ready not only makes the process smoother but also allows you to focus on doing the job right without interruptions.
Start by grabbing a garden fork or spade, which will help you dig up the rhizomes carefully without causing any damage. You’ll also want to have a sharp knife on hand. A sharp blade is crucial, especially if the clumps are tough to separate by hand. Clean cuts are important because they minimize the risk of tearing the rhizomes, which can leave them vulnerable to bacterial infections. Lastly, don’t forget a sturdy pair of gloves to protect your hands while you work.
2: Digging Around the Iris Clump
Now that you have your tools ready, it’s time to start digging around the iris clump. This step is crucial for safely removing the rhizomes without damaging them.
Positioning Your Shovel
Begin by positioning your shovel a few inches away from the clump. This ensures you won’t accidentally cut into the rhizomes. Look for the older rhizomes in the center and work your way outward.
Using the Right Shovel
I like to use a smaller shovel for this task. In fact, I often use a child-sized shovel because it’s easier to handle and less strenuous on my back. This smaller size helps you dig more precisely.
Carefully Loosening the Soil
Gently work your way around the clump, loosening the soil as you go. If you accidentally chop off a few leaves, don’t worry. This usually means you need to dig a bit further out. The goal is to free the clump without damaging the rhizomes.
Once the soil is sufficiently loosened, you should be able to pull the clump out with minimal effort. If the roots are well-established, this is a good sign of a healthy plant.
3: Breaking Apart the Clumps
Once you’ve dug up your iris clumps and trimmed the leaves, the next step is to break apart the clumps. This is a key part of ensuring that each division has enough resources to grow into a strong, healthy plant.
You have a couple of options for breaking apart the clumps. If the clumps are small enough, you can do it by hand, gently pulling them apart.
For larger, tougher clumps, use the blade of a spade to roughly divide them into more manageable pieces.
As you start to break the clumps apart, look for natural divisions in the rhizome where it can be easily separated.
Gently pull the clump apart by hand, or carefully cut through the rhizome with your disinfected tool if needed. The goal is to end up with individual rhizomes that are ready to be replanted.
4: Selecting Healthy Rhizomes to Keep
After breaking apart the clumps, the next step is to choose the healthiest rhizomes for replanting. This part is important because it ensures that only the best and most vigorous parts of the plant get a chance to thrive in your garden.
When you’re selecting rhizomes, look for a few key things. Healthy rhizomes should feel firm to the touch, with a light color that signals they’re in good shape. A strong root system is another must—those roots will be crucial as the plant settles into its new spot. Also, make sure the rhizomes have a fan of leaves with at least four or five leaves. That’s a good sign that the plant is ready to grow and bloom.
Toss out any rhizomes that have holes in them. These holes are a clear sign of damage from the iris borer (Macronoctua onusta), a pesky caterpillar that starts by chewing through the leaves and then burrows all the way down into the rhizome.
As you sort through, don’t be afraid to discard any rhizomes that are soft, have dead roots, or don’t have a decent leaf fan. These are less likely to take off and produce the flowers you’re hoping for.
You’ll also come across some smaller rhizomes that may not have as many leaves. While you can still plant these, they might take longer to flower. If you have plenty of healthy, larger rhizomes, it’s often better to focus on those for a more immediate impact in your garden.
And one more thing—rhizomes that have already flowered won’t bloom again, so it’s best to remove them from the bunch. You can usually tell these by the presence of old flower stalks or dead roots.
5: Trim the Leaves
After separating the rhizomes, it’s important to trim the leaves. This helps prevent the plants from toppling over when they are reintroduced to the soil. This reduces their weight and helps the plant focus on root development.
- Trim the Leaves: Use a pair of sharp scissors or pruning shears to cut back the leaves to about one-third of their original height.
- Dispose of Trimmings: Collect the trimmed leaves and add them to your compost pile or dispose of them properly.
6: Clean and Cut Back Roots
Before replanting, it’s important to clean and trim the rhizomes to ensure they’re healthy and ready for their new spot in the garden. Start by gently brushing off any excess soil from the rhizomes. This not only helps with handling but also allows you to inspect them closely for any signs of disease or pests.
Next, use garden shears to trim the roots back to about a third of their original length. This root pruning helps the plant focus on establishing new roots in its new location, giving it the best chance to thrive and bloom beautifully.
7: Replant Divided Rhizomes
Now that you’ve selected the healthiest rhizomes, it’s time to get them planted so they can settle in and prepare for a beautiful bloom in the coming seasons.
Start by finding a sunny spot in your garden with well-drained soil. Irises love full sunlight, and good drainage is key to preventing root rot. Loosen the soil and mix in some compost to create a nutrient-rich environment that will help your rhizomes establish strong roots.
When you’re ready to plant, dig holes that are about four to six inches deep and space them twelve to eighteen inches apart. This spacing ensures your irises have plenty of room to grow without crowding each other.
The holes should be deep enough to accommodate the rhizomes without burying them too deeply. The top of each rhizome should sit just below the soil surface.
As you place the rhizomes in their holes, make sure the roots are spread out and the leaves are pointing upward.
Position the new shoots in the direction you want the plant to grow. Once everything is in place, cover the rhizomes with soil, pressing it down gently to eliminate air pockets and ensure good contact between the roots and the soil.
8: After care
After planting, be sure to water the area thoroughly to help the soil settle nicely around the roots. For the first few weeks, keep the soil consistently moist but not waterlogged—this encourages the rhizomes to establish strong, healthy roots. Once your irises are established, they’ll become relatively drought-tolerant and won’t need as much frequent watering.
To help retain moisture and keep weeds at bay, apply a light layer of mulch around the plants. Just be careful not to cover the rhizomes themselves, as that could lead to rot. Regularly check for weeds and remove them promptly so they don’t compete with your irises for nutrients. During dry spells, keep an eye on your irises and give them a drink if needed.
As your newly planted rhizomes start to grow, you should see new leaves and shoots emerging within a few weeks. If any plants show signs of stress or disease, address the issue immediately to ensure the overall health of your garden.
