How to divide irises and replant them in the garden
The blooming of the bearded irises is something I eagerly await each spring. This year, I made a mental note that I should divide and replant the irises in later summer, after flowering. The time is now! Here’s how to divide irises—with step-by-step pictures.
Even though my irises were planted years ago and are terribly overgrown, the blossoms were still gorgeous this spring. But dividing bearded irises every three to five years allows the clump to rejuvenate and bloom better (not to mention a way to multiply your irises to fill in gap). Also, it’s helpful to avoid the iris borer which is a very destructive pest typically attracted to older, over-crowded gardens.
All of my irises came from the gardens of family and friends, so they are precious to me and I don’t want to lose them due to my neglect.
When Should You Divide Irises
It’s important to divide and replant at the right time of year. In many regions, July and August are the best months to dig, divide and transplant bearded irises. You can probably get away with dividing through mid-September, too. Do NOT divide in the spring. You must do this job post flowering, during the summer.
This is hot, heavy work involving a lot of digging, so I waited until the weather cooled down a tad before starting. My goal was to rework the iris beds, add some compost, get rid of the invading sedums and tree roots, and divide and replant the crowded rhizomes.
The irises are getting crowded and encroached upon by pachysandra. The bed they are in is narrow and next to large rocks leaving the irises nowhere to go.
Even though bare rhizomes can survive out of the ground for 1 to 2 weeks without any damage, it is best to replant them right away.
How to Divide Bearded Irises
First, dig the rhizomes up and check them for disease or insect damage. Try to dig carefully around the plants so as not to do any unnecessary damage to the rhizomes.
We found some borer damage and mushy rhizomes that were discarded.
Snap or cut off the old part of the rhizome, since it will not flower again.
The roots are quite long and will help anchor the newly planted rhizome in place.
Amend the soil with compost and dig a shallow hole or trench. Make a mound of soil in the middle to place the rhizome on, spread the roots out over the mound and cover them with soil.
Leave the top of the rhizome exposed.
Next season’s plant emerges from the fan end of the rhizome so when replanting, face it in the direction you want plant growth to travel. Space the pieces 12 to 24 inches apart for tall types, closer for dwarf ones.
I planted mine closer, for a more immediate display, knowing that I will have to divide them again sooner.
It is easier to plant if you cut the tops back to about 6 inches tall.
Water well to settle the soil around the roots and continue to water deeply once a week until new growth appears. Once established, bearded irises are drought-tolerant and won’t need additional watering. Fertilize early in spring and again right after blossoming with compost or a low nitrogen fertilizer.
It was sweaty work, even on a cool day, but so rewarding to see it done. We had enough leftover rhizomes to plant another bed on the other side of the stone wall. Next spring we should have twice the blossoms!
Learn more about growing irises in the Almanac’s Iris Growing Guide.
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The next to last picture and the last picture show different soil levels. Should the tuber be covered with soil, or not? What about wood chip mulch?
The next to last picture is to show how the tubers were placed. In the last picture some of them have been covered with a thin layer of soil, which is okay. Much of it gets washed away when watering or during a rain storm. The trick is not to deeply bury the rhizomes. When you mulch, try not to cover the rhizome. Just put it on the bare soil around the plants.
Thank you! I'm leaving the state and going South soon! plan to bring some of them down there in my garden there ! I did not know about cutting the tops off. THIS WAS VERY INFORMATIVE and HELPFUL to me ! Thank you for having this for us faithful gardeners out there ! Does anyone know why my bearded irisses did not bloom this year ? A lady in my church said they only bloom every 4 years ? I never heard of that. They did bloom last year ! All of them! I do feed them in March and June. as all my plants.
I have known for a long time that iris should be divided in August, but never found any detailed instructions for how to go about it. Robin to the rescue! Thank you so much for the invaluable step by step direction with great photos!
I have Siberian irises. Noticed someone asked about dividing those. It's similar, but I didn't get small, tidy, individual stalks to replant. After 5 years, they slowed blooming and I could see the center was dead, an outer ring still green = time to divide. Ugh. Big chore. I only had 3 of them. Each had to weigh 40 pounds by the time I got them out, loaded with soil in the roots, etc. Tried different methods to separate clumps and get rid of the dead areas and after failing and struggling many times, I settled on a handsaw! Should have thought of that first. It worked. Put them all on tarps - lots of dirt, easier to clean up. Replanted the vigorous growth, dumped the dry, had lots for the back yard and front. The first spring, however, this year, only two flowers showed up after all that stress. The foliage is looking good, though. I'm feeling confident that they'll come back next year with a nice bloom. But seriously, be very cautious dividing irises or hostas or any well established perennial. I hurt my shoulder badly. Pinched a nerve. Weeks to feel better. Of course, that's just a cautionary message from a middle age dude! I should have grabbed that saw first thing. At least it's something that only has to be done every 3 to 5 years!
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