Transplanting and Dividing Iris
Recommendations for when to divide irises depend on the species. Follow these tips to maintain a colorful, attractive iris planting.
Bearded Iris
Bearded irises are one of the most popular and widely grown perennials in the home landscape. While bearded irises are beautiful, they do require moderate levels of maintenance. One important chore is to divide bearded irises. If not divided, the plants become overcrowded and flower production decreases. Crowded plants are also more prone to foliar diseases.
When to Divide Bearded Iris
Bearded irises should be divided every three to five years, as the plants quickly become overcrowded and don’t bloom well. July or August is the best time to dig, divide and transplant bearded irises.
How to Divide Bearded Iris
Bearded irises grow from thick, fleshy, underground stems called rhizomes. Carefully dig up the iris clumps with a spade. Cut the leaves back to 1/3 their original height. Wash the soil from the rhizomes with a forceful stream of water from the garden hose. Then cut the rhizomes apart with a sharp knife. Each division should have a fan of leaves, a healthy rhizome, and several roots. Discard the old, leafless rhizomes in the center of each clump. Also, discard all diseased and insect damaged rhizomes.
When planting bearded irises, dig a hole large enough to accommodate the rhizome and roots. Build a mound in the center of the hole. Place a rhizome on top of the mound and spread the roots in the surrounding trench. Point each fan of leaves away from the other irises in the group. Then cover with soil. When planted, the large fleshy rhizome should be just at or below the soil surface. Finally, water each plant thoroughly.
Divided irises typically bloom sparsely the following spring. However, plants should be in full bloom by their second year.
Best Growing Conditions for Bearded Iris
Bearded irises perform best in fertile, well-drained soils and full sun. The planting site should receive at least six hours of direct sun per day. Plants that don’t receive sufficient sunlight will not bloom well. Bacterial soft rot is often a problem in wet, poorly drained sites. Wet, poorly drained sites can often be improved by incorporating organic matter, such as sphagnum peat moss or compost, into the soil prior to planting. Raised beds are another option for gardeners with poorly drained soils.
To obtain a good flower display, plant at least three rhizomes of one cultivar in a group. Space the rhizomes 12 to 24 inches apart.
Siberian Iris
Siberian iris are great additions to the garden. Their flowers resemble those of bearded irises but are smaller and lack fuzzy beards. Brilliant blue, white, lavender or yellow flowers appear 1 to 3 weeks later than bearded iris. Leavea are more grass-like and dark green. They are a great alternative to bearded iris in areas with heavy soils or poor drainage as Siberian iris prefers wet conditions.
When to Divide Siberian Iris
Siberian irises don’t have to be divided as often as bearded irises. It’s advisable to divide Siberian irises when clumps become crowded, plant vigor declines or clumps have formed solid rings with bare centers. Siberian irises can be divided in early spring or late summer.
How to Divide Siberian Iris
When dividing Siberian irises in early spring, dig up the entire clump when new growth has just begun to appear. Divide the clump into sections with a soil knife or spade. Each section should have several growing points and a good root system. Replant immediately.
When dividing plants in late summer (August), dig up the entire clump, cut back the foliage to 6 to 8 inches and divide the clump into sections with each division containing several fans of leaves and a good root system. Promptly replant the divisions.
Best Growing Conditions for Siberian Iris
Siberian irises grow and bloom best in full to part sun. Plants prefer moist, fertile soils and are suited to edge of ponds and streams. While they don’t mind wetter conditions, they also grow well in average moist, well-drained soils.
More Information
Photo credits: 1: Aaron Steil; 2: Aaron Steil; 3: Maren Winter/AdobeStock
Don’t Wait! Here’s Exactly When and How to Divide Your Irises
If your once-thriving iris bed has started to look a little lackluster—or the blooms just aren’t what they used to be—chances are, it’s time to divide them. While irises are famously low-maintenance, they do need a little attention every few years to keep performing their best. The good news? Dividing irises isn’t hard. In fact, doing it at the right time can reward you with healthier plants and even more spectacular blooms.
Let’s walk through exactly when and how to divide your irises without breaking a sweat.
Why Do Irises Need Dividing?
Over time, iris rhizomes (the thick underground stems) multiply and crowd each other out. This can lead to:
- Fewer or smaller flowers
- Weak or floppy stems
- Clumps that look crowded or overgrown
- Increased risk of rot or disease
When irises outgrow their space, they compete for nutrients, sunlight, and airflow. Dividing them helps relieve that congestion and gives the healthiest rhizomes room to grow and bloom like crazy.
When Is the Best Time to Divide Irises?
Late summer to early fall is the sweet spot—typically 4 to 6 weeks after blooming ends, when the plants are entering dormancy but still have time to establish before winter.
Best months by zone:
- Zones 3–5: Late July to early September
- Zones 6–7: August through mid-September
- Zones 8–10: September to October
Avoid dividing in spring or while the irises are actively blooming. Doing so can stress the plant and reduce flowers the following season.
What You’ll Need
Before you dig in, gather a few garden tools:
- Garden fork or spade
- Sharp knife or pruners
- Gloves (iris leaves can be sharp!)
- Bucket of water (for soaking, if needed)
- Optional: sulfur powder or antifungal dust
Step-by-Step: How to Divide Irises
1. Dig Up the Iris Clump
Use a garden fork or shovel to gently loosen the soil around the iris clump. Dig wide and deep enough to avoid damaging the rhizomes. Carefully lift the entire clump out of the ground.
2. Shake Off the Soil and Rinse
Brush off the loose dirt or hose the clump down so you can clearly see the rhizomes and roots.
3. Trim Leaves and Roots
Cut the leaves back to about 6 inches, forming a fan shape. This reduces water loss and helps the plant focus on root growth. Trim off any long or stringy roots.
4. Separate the Rhizomes
Break apart or cut the clump into individual rhizomes. Each piece should have:
- A firm, healthy section of rhizome
- At least one fan of leaves
- Some root growth underneath
Toss any soft, mushy, or rotten rhizomes—they won’t grow back.
5. Optional: Treat with Antifungal
Dust the cut ends with sulfur or antifungal powder if rot has been a problem in your garden. Let the rhizomes dry for a few hours before replanting.
How to Replant Divided Irises
Choose a sunny, well-drained spot. Irises love at least 6 hours of full sun a day and hate wet feet.
Planting Instructions:
- Dig a shallow hole or trench
- Create a small mound of soil in the center
- Place the rhizome horizontally on the mound
- Spread the roots down the sides
- Cover the roots—but leave the top of the rhizome exposed
Water lightly and keep the area moist (not soggy) for a few weeks as the roots settle in.
Where Should You Replant Them?
You can put the divided irises:
- Back in their original bed (with more spacing)
- Into new spots around the yard
- In containers for patio color
- Or share extras with friends and neighbors!
Pro tip: Space rhizomes about 12–18 inches apart to give them room to multiply again without crowding.
Iris Dividing FAQs
How often should irises be divided?
Every 3 to 4 years is ideal for most varieties, especially bearded irises.
Can I divide irises in spring?
It’s not recommended. They may survive, but dividing during dormancy (late summer/fall) leads to healthier plants and better blooms.
Will they bloom next year after dividing?
Yes—if replanted promptly and in the right conditions, they’ll often bloom the next season.
Final Thoughts: Don’t Wait Too Long
If your irises look crowded, sad, or bloomless, don’t chalk it up to bad luck. Dividing them at the right time could be the simple fix they need.
Give them a little space and some fresh soil, and they’ll reward you with armloads of gorgeous blooms year after year. So grab your gloves, mark your calendar, and let those irises shine again!
https://yardandgarden.extension.iastate.edu/how-to/transplanting-and-dividing-irishttps://thegardenbeds.com/2025/06/08/dont-wait-heres-exactly-when-and-how-to-divide-your-irises/
