By Jennifer Poindexter
Do you grow irises around your home or in a garden bed? Do you enjoy their vibrant beauty and how easy they are to care for?
If you’ve grown iris flowers for any length of time, you’ve probably acquainted yourself with the anatomy of this plant.
You know it has beautiful green foliage which produce a range of colorful blooms. You also know the base of the plant, where the foliage starts, is called a rhizome that leads into the plant’s root system.
Why is this important? Because over time, the rhizome will stop producing. If you’d like to learn how you can keep your irises blooming for years to come, you need to know how to properly divide the rhizomes.
Here’s what you must know to divide your iris flowers’ rhizomes to produce even more plants and color around your home or garden:
Why Divide Rhizomes of the Iris Plant?
As your iris plant becomes established, the rhizome will grow along with it. During this growth process, the “mother” rhizome reproduces baby rhizomes.
This will lead to more foliage and blooms producing in the grow space. Eventually, the mother rhizome will run its course.
Overtime, the original rhizome will stop producing new rhizomes, blooms, and foliage and eventually die.
When you see this beginning to happen, it lets you know it’s time to divide the mother rhizome. This will allow the newer rhizomes to grow, bloom, and take on the “mother” role.
The Process of Dividing the Iris Plant Rhizomes
Now that you understand why dividing rhizomes is important, you must understand the proper technique to performing this task. You don’t want to begin hacking into your plants and ruining your flowers.
By following these steps, you should have an easier time dividing the rhizomes and have a greater chance at reducing harm to your plants.
1. Out with the Old Iris Plant Rhizome
When you see the mother rhizome starting to die back and failing to produce new foliage or blooms, it’s time to begin the division process.
Start by digging up the old rhizome. Use a shovel, spade, or pitchfork to dig beneath the earth and pull out the mass of rhizomes.
The idea is to use the tool that makes the cleanest cut through the rhizomes to pull them out of the earth with little to no damage.
Once you’ve gotten beneath the mass, made your cut, and have heaved it up from the earth, you should be staring at a large clump of rhizomes. If you’ve made it this far, you’re starting off on a positive foot in this process.
2. Separate the Iris Plant Rhizomes
The next step in the division process is to separate the mass of rhizomes into individual rhizomes. Depending upon how firmly clumped they are, will determine how you go about separating the mass.
If the rhizomes are loosely clumped together, you should be able to use your hands to carefully pull them apart.
However, if the mass is woven tightly, you may need to use a sharp knife to separate it. It’s vital to sanitize your knife in a bleach solution between cuts.
If you slice into a rhizome that is infected, and don’t sanitize your knife between cuts, you can spread the disease to other rhizomes. The sanitizing solution should be one-part bleach to ten parts water.
Once your rhizomes are separated, begin looking at them to see which are healthy and which are not. A healthy rhizome will be approximately two inches in diameter, have a strong root system, and two or more leaves on it.
If the rhizomes don’t appear young and healthy, get rid of them because they most likely won’t form healthy plants.
This is also the time to discard the mother rhizome. She’s served her purpose and shouldn’t be intertwined with the new rhizomes for transplanting.
After reviewing your newly separated rhizomes, you’re ready to move forward in the process.
3. Remove the Dirt of the Iris Plant Rhizome and Inspect
You’ve separated your rhizomes and separated the weak from the strong. It’s now time to pull the dirt back and look even closer to make sure you’re only saving the healthiest of rhizomes from each clump you’ve removed from your garden space.
Wipe the dirt off the rhizomes you saved and begin inspecting them for pests. Iris borers can cause serious issues because they feed off the rhizome.
If you see any iris borers, kill them between your thumb and index finger. Look closely at the rhizome you found the pest dwelling on. If the rhizome looks healthy, keep it. If the borer has caused damage, it’s better to toss that rhizome.
Once you’ve inspected each rhizome, it’s time to disinfect them. Gently rinse each rhizome with a bleach disinfectant.
Again, make sure it’s one-part bleach to ten parts water. This can help ward off any diseases that may try to ravage your newly transplanted rhizomes.
After disinfecting, check your rhizomes one more time. If any have a bad odor about them or feel squishy, they don’t need to make the cut for transplanting.
4. Trim the Foliage of the New Iris Plant Rhizomes
Your rhizomes are clean, disinfected, and thoroughly inspected. What could possibly be left? All they need now is a trim.
This isn’t for aesthetics. Instead, by trimming the foliage back to only three to six inches in length, it allows the plant to put all its energy into establishing a solid root system.
If you leave the foliage longer, the plant will send nutrients to it because it thinks it’s still trying to maintain quality health in this area.
By cutting the foliage back, it sends a message to the plant to divert the energy to the roots because that’s where it’s really needed.
After you’ve trimmed each rhizome’s foliage back to only a few inches, they’re ready for transplant.
5. Transplant the New Iris Plant Rhizomes
Transplanting an iris rhizome isn’t a complicated process. You should find a location that provides well-draining soil and ample sunlight.
The rhizome needs approximately six hours of full sun per day. These two grow requirements are vital to ensure the rhizome remains dry to avoid rot.
Also, more sunlight equates to more blooms. If you want the most color you can get from your irises, keep them healthy and provide the light they desire.
When it’s time to dig the holes for transplant, ensure they’re approximately four inches deep and at least two feet apart.
You might be able to get away with them being a little closer if you choose a miniature variety of the iris plant.
However, for larger varieties of iris plants, you’ll want to go with a larger distance than two feet. Once the holes are dug, place the rhizome into the space.
Ensure the rhizome is erect while the roots are spread out. The rhizome should be sitting at soil level where you can see at least one to two inches of it.
This will ensure it receives proper sunlight while also avoiding putting too much pressure on the roots. If the rhizome isn’t sitting high enough, the roots can become compressed in the space.
When all the rhizomes have been planted, water them well. Irises only need water during drought and right after transplant. By watering them during this time, you’re doing your part to give these plants a proper start.
Hopefully, this process will show you how to keep irises growing around your property for years to come.
Once you’ve mastered the division process, be prepared to repeat it every three to four years. This will keep your home booming with color all summer long.
More About Dividing Rhizomes of the Iris Plant
https://extension.psu.edu/dividing-irises
https://extension.umd.edu/hgic/topics/dividing-iris
When I cut the back, can I use a weed eater to cut them back?
I’ve read that the smaller rhizomes attached to the mother rhizome are the ones to separate and replant They normally have no particular roots of their own. I’m confused because there would be no roots to spread around. Can you elaborate?
Diane Honaker: I think this article is more about what people do when they enjoy seeing irises growing in their gardens.
If you really don’t like having irises around, then yes, you could cut them back with a high-speed weed whacker, as you suggested. The only problem with this, I think, is that there might still be a few parts of the plant left intact in the ground, and a few of them might foolishly struggle to grow back the following spring. A couple more years of the weed whacker will take care of them, though.
People who really hate irises might be better off simply digging up the rhizomes. They haven’t been buried deep underground; they’re right there under a couple inches of topsoil, so it should be easy.
If you really don’t like flowers at all, the easiest thing would be to pour gasoline over the area, set it on fire, and then pave it with concrete. Note: This is at your own risk, since gasoline is highly flammable and it is likely to burn down anything nearby, including your house, any neighboring trees or wildlife, pets, any toddlers that might wander into the area, older children staring at their phones instead of watching where they’re going, friends and family members, your neighbor, your neighbor’s house, any automobiles or vehicles in the area, utility poles, and the weed whacker.