While summer is normally the time to kick back and enjoy the literal fruits of your labor, there may still be a few gardening tasks lurking—such as that overgrown patch of past-bloom irises that need to be divided. Now is the right time.
Maybe they are too crowded, maybe they aren’t blooming as much as before, or maybe it’s been three to five years since they were last divided—all are good reasons to divide your irises. While there are hundreds of varieties of irises, these instructions apply to one of the most common varieties: the tall bearded iris.
Photography by Joy Yagid, unless otherwise noted.
Above: Bearded irises edge a narrow path at Tattenhall Hall in Cheshire, England. Mid to late summer is the best time to divide them because the plants are starting to go dormant. They are winding down from putting on a show in the spring and are building up reserves for next year’s show. Photograph by Clare Coulson, from Cult of the Bearded Iris.
Step 1: Dig up the irises.
Above: How overgrown your iris patch is will determine what tools you’ll need. A heavily crowded patch may need a garden fork to lift the rhizomes up as one huge mass. A trowel can get beneath smaller clumps. Whichever you choose, the goal is to limit damaging the rhizomes.
Step 2: Find the healthy rhizomes.
Above: Once all the rhizomes have been lifted out of the ground, brush the soil off of them. Assess what you have. Discard the mother rhizomes; rhizomes bloom only once, so you’ll want to replant with the daughter offshoots. Also toss rhizomes that are mushy and rotten, have iris borer damage, or lack fans of leaves (see below).
Step 3: Keep a fan of leaves with each division.
Above: Once you have removed the damaged and diseased parts, look at what’s left. You want to divide them in such a way that each section has a fan of leaves growing from it. Some may have buds where next year’s rhizomes will sprout. If the buds are on a section that has a fan, keep them with the fan. Don’t divide them. They are not fully formed yet and it’s better if they are kept with the section with the fan.
Step 4: Divide the rhizomes.
Above: The actual dividing is simple; you can snap them like a carrot, or use a sharp knife.
Step 5: Trim the leaves.
Above: Once you’re finished dividing, trim the leaves. Cut them back by two-thirds and into a fan shape. This helps the plants by reducing the amount of leaves it needs to support. Dividing and transplanting can stress plants. Make it easier on them by giving them a bit less work to do.
Step 6: Replant the divided rhizomes.
Above: Then replant them in well-draining soil, making sure the top of the rhizome sits above the ground. Water well. Or you can hold off replanting them for up to two weeks. (This is what I’ll be doing while I redo my flower bed.)
Step 7: Be patient.
Above: Since dividing does divert the plant’s energy to becoming reestablished, the following year may see less flowers. However, following years should reward you with brilliant blooming.
Dividing tall bearded irises helps rejuvenate the plants, promotes better flowering, and prevents overcrowding.
When is the best time to divide tall bearded irises?
The best time to divide tall bearded irises is in late summer or early fall, after they have finished blooming.
How often should I divide tall bearded irises?
Tall bearded irises should be divided every 3 to 4 years to maintain their health and vigor.
How do I prepare the irises for division?
Start by cutting the foliage down to a height of about 6 inches. Then, carefully lift the clump of irises out of the ground using a garden fork or spade.
How do I divide the iris rhizomes?
Gently separate the rhizomes by hand or use a clean, sharp knife to cut them into smaller sections. Ensure that each section has at least one fan of leaves and healthy roots.
What should I do with the divided iris rhizomes?
Trim the leaves to about half their original length and remove any damaged or diseased parts. Allow the rhizomes to dry for a few hours before replanting or storing.
Where should I replant the divided irises?
Choose a sunny spot with well-draining soil for replanting the divided irises. Space them about 12 to 18 inches apart to allow for adequate growth.
How should I care for the newly divided irises?
Water the newly divided irises thoroughly after replanting. Provide regular watering during the first growing season and apply a balanced fertilizer in early spring.
What should I do with the excess divided iris rhizomes?
If you have more divisions than you need, consider sharing them with gardening friends or donating them to a local plant sale. Alternatively, you can store them in a cool, dry place for future use.
How long does it take for divided tall bearded irises to bloom again?
After division, tall bearded irises may take 1 to 2 years to fully establish and bloom again. Be patient and continue to provide proper care during this period.
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