If you grow irises, you’ll get to the point when dividing them becomes necessary. There are four telltale signs that will let you know when it’s time for transplanting iris.
If you notice fewer blooms, overcrowded clumps, and rhizomes pushing out of the soil, these are indications that your irises need more space to grow.
Another indicator of when to split irises lies in the clump itself. If the center starts to die out and there is only healthy growth around the outside, it’s time to transplant!
Don’t get discouraged if this happens to you. Transplanting irises is very easy to do and is a part of maintaining this popular popular perennial.
Keep reading to learn when to transplant iris, why it’s important, and get step-by-step instructions on how to do this.
Why do irises need to be divided?
Most irises grow from underground roots known as rhizomes. Over time, these rhizomes will multiply, becoming woody and overcrowded.
When this happens, flowering slows down, the roots have less circulation around them and the rhizomes are more susceptible to disease.
Dividing the irises rejuvenates the plants, giving them better access to nutrients. This leads to healthier plants and more blooms.
Dividing and transplanting irises should be done every three to four years.
When to transplant iris
Depending on where you live, the best time to transplant irises is midsummer or early fall. Split and transplant irises 6-8 weeks after they finish blooming when the foliage starts to die back.
Dividing irises at this time allows them to recover and establish strong roots before winter arrives. Cool fall weather reduces the stress on the plant.
Can you transplant iris in spring?
I prefer not to transplant in early spring.
The main period of root growth is about to start, which is good for the rhizomes. However, dividing irises in the spring makes it unlikely that you’ll get flowers in the first year.
Also, iris plants that have been divided and transplanted in spring will need to be staked, whereas irises divided in the fall will not.
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How to divide irises
You’ll need a few tools to transplant your irises:
Using your garden shovel, dig up the entire clump of irises by digging around the perimeter and using the shovel to pry the whole clump out of the ground. Try to get as many roots as possible.
Knock off any excess dirt. This will allow you to inspect the clump of rhizomes.
The old woody center section should be discarded. Also discard any rhizomes that are soft, diseased, or insect-damaged.
Now it’s time to divide the rhizomes. Cut them apart with a sharp knife. Each division should have a healthy rhizome, with roots and some trimmed foliage.
Cut the foliage back to 1/3 of its original height. This step reduces water loss and prevents the plant from flopping over after replanting. Typically, the leaves are cut in a fan shape, which looks like an inverted V.
How to transplant irises
Plant your iris divisions in a spot that receives at least 6-8 hours of sunlight daily.
Choose loose, well-draining soil that has been amended with compost or other organic matter. A slightly acidic to neutral soil is beneficial (pH 6.0-7.0).
Space the rhizomes about 12-18 inches apart and plant them just below the soil surface with the tops slightly exposed. Point the fans of the rhizomes away from each other.
Cover the rhizomes with soil, but leave the top slightly above the soil level. This helps to prevent rotting, allows them to stay dry, and promotes better flowering.
Burying iris rhizomes too deeply can lead to moisture buildup. They need good air circulation and sunlight to stay healthy.
What to expect after dividing irises
You should see new growth within 2-3 weeks. The first sign that the transplants have taken is a single leaf appearing in the center of the rhizome.
You can encourage this by watering well until the leaf appears. Then you can reduce the watering.
Some iris transplants will bloom the first spring after planting. However, depending on your growing conditions, it is possible that you won’t get flowers until the second year.
Even though they will show growth after being transplanted, you should still cut the foliage back in the fall, as you do with all irises.
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Admin note: This post answering the question “When do you transplant irises?” originally appeared on the blog in April 2013. I have updated the post to add all new photos, a printable project card, and a video to enjoy.
How to Divide and Transplant Iris Rhizomes
You may find yourself wondering when to split irises and move them.
At some point, your irises will become woody and overcrowded. They will stop flowering when this happens.
Fortunately, transplanting irises is an easy thing to do. This tutorial shows how.
Print out the instructions and keep them in your gardening journal.
Materials
- Iris rhizomes
Tools
- A shovel
- Garden shears
- Sharp knife
- Garden gloves
- Garden hose or watering can
Instructions
- Use a garden shovel to dig around the entire clump of irises.
- Pry up the clump using the tip of the shovel. Try to get as many roots as possible.
- Knock off the excess dirt.
- Examine the rhizomes. Discard any that are soft, diseased, or insect-damaged.
- Cut the foliage to 1/3 of its original height in an inverted V-shaped fan.
- Be sure each division has a healthy rhizome, some roots, and a fan of leaves.
- Choose a spot that gets 6-8 hours of sunlight.
- Add compost to the hole and place the rhizomes 12-18 inches apart, just below the soil surface with the tops slightly exposed.
- Point the rhizome fans away from each other.
- Water well until you see new growth in 2-3 weeks.
- The iris divisions may flower the following spring, or flowering might not occur until the second year.
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Heather @ new house new home new life
Wednesday 7th of May 2014
I'm waiting for my transplanted irises to do the same thing. Someone told me that in order to get a bloom, the plant must have clusters of five leaves. So I've been busy counting leaves on my morning walk around my garden.
admin
Wednesday 7th of May 2014
I've never heard that Heather. Good to know. I just dug 'em up and transplanted. I figured that ANYTHING was better than where they were (in caliche soil with no water.)
Carol