How to Raise and Divide Irises
Dividing Irises Is Easy
The best time to divide irises is July through September. If you live in the South, however, they can be divided throughout the winter, but they may not bloom the following spring.
I originally wrote this article when living in north central Alabama, but after seven years in central Florida, we now live in coastal Alabama. They lived a few years in Florida, but got progressively smaller each year until finally dying. I moved some irises in January of 2014, and, to my surprise, one of them bloomed the following April. Usually when moved that late, they pout, and refuse to bloom that spring.
This article is about much more than how to divide irises. I will share what I have learned not only about how to divide irises, but also about raising irises, including their requirements, their tolerances, how to plant them (it's not the usual way), and even when to trash them.
I have been raising and dividing irises for many years, and have learned a lot about what works with them and what does not. They are easy to grow, drought-tolerant, and not overly choosy about their soil. Of course, the better the soil, the better they will grow, bloom, and show off for you.
I gained a love of bearded irises from my mother. Many people think of irises as old-fashioned flowers, but I find them to be exotic-looking and magnificent. They are one of many plants that gardeners often refer to as "pass-along plants" because they can be passed along from one gardener to another without harming the parent plant. That is how I received many of my irises, but first they must be divided.
Irises' Most Important Needs
Irises have few needs. But they really need those few things:
- Full sun — this means no less than six hours of sun per day.
- Well-drained soil.
- Rhizomes partly above the soil.
- No mulch on the rhizomes.
Rhizomes and Roots
In the above photo, you see the rhizome and roots of an iris. The large brown part is the rhizome. The long slender roots are the only part that should be underground. When planting them, sprinkle a good granular or polymer-coated fertilizer in the soil, and water it in. I use Osmocote, shown near the end of this article.
Properly planted irises should look like little potatoes lying on the ground, as shown in the next photo. These are very drought-tolerant plants. So, if planted underneath the soil, or if mulched, the rhizomes will rot due to too much moisture.
Irises Too Crowded
The above photo was taken in February or March after a very mild winter. The irises had just begun a period of new growth. They appeared to have been planted correctly by the previous owner of this property, but they had grown far too crowded. It was past time for them to be divided.
Again, the best time to do this is from July through September, but it can be done at any time. I usually do it in late autumn or late winter because it is often too hot from July through September. However, if done in late winter or early spring, they often will not bloom that spring.
A Temporary Fix for Over-Crowded Irises
If you do not have time to dig up the irises and separate them, there is another way. Be aware this is only a temporary fix.
Take a good look at your crowded irises. You will see some of the older, original rhizomes, from which newer plants have grown. Now that the newer plants are large enough, the older, "parent" plant can be removed. In this photo I circled in yellow some older rhizomes to be removed. The pink circles are around two plants that I dug up and placed in another bed. The others I left in the same location until I decided what to do with them.
Take a sharp knife or, if stooping down is a problem for you, use a sharp shovel to sever the connection between the parent plant and the younger off-shoot plants. Then simply pick up the older rhizome and examine all sides of it.
If that older rhizome has little rows of holes made by iris borers, (they're usually on the bottom) or if it is shriveled, soft, or has any wet rot, put it into the trash can. DO NOT put into your compost bin, because you could introduce the borers or any mold or disease from the rot into your compost.
On the other hand, if it has a tiny new sprout on the side, give a chance. Plant it and see what happens. If it has no roots, just lay it on bare soil, and press some soil up to it, but do not cover it — I have actually seen these plants take root when just lying on the ground. Then just give nature time to do her work.
Never Mulch Irises
Iris rhizomes should never be mulched. This encourages moisture which will cause them to rot.
The above photo is an example of wet rot from too much moisture. This iris was probably planted in a good place, but mondo grass nearby had encroached on the irises in this bed. One of them had to go. It was the mondo grass. Another problem causing wet conditions were the weeds and leaves that needed to be removed. In autumn, be sure to remove fallen leaves from around your irises.
As you can see, the entire rhizome had not been damaged, so it can be cut or broken off at the point where the yellow line is drawn. The rotted portion should be trashed, then the remainder of the rhizome planted in a sunnier spot away from weeds and invasive plants such as mondo grass.
The rhizomes should look like little potatoes lying on the ground, with only the long slender roots beneath the soil. --Maria
Never, ever put mulch
of any type on top of
your iris rhizomes.
I ordered a group of six irises from Springhill Nursery — one each of six colors: burgundy, purple, blue, white, yellow/purple, and orange.
The orange one was a free "bonus". This white/purple wasn't one of them. There was a white one that appeared to have died. Then this one came up in its place. Imagine my surprise when it bloomed.
I suppose it is possible that the growers sent me the wrong one. Of the six plants, only 4 survived. The free one and the burgundy one quickly shriveled up and rotted.
Osmocote: My favorite fertilizer for perennials:
Iris Day Is May 8
Did you know there is an Iris Day? It's May 8th every year, and is celebrated from late April through mid-June worldwide with festivals that include art shows, fun runs, beauty pageants, and much, much more.
This photo is of another iris whose name I don't know. It was on the property of our former home when we bought it. It didn't bloom the first year we were there, then we had some tree limbs removed and, with the additional sunlight, it began blooming each spring. Those irises demand their sunshine!
These are some of my favorite gardening tools:
Digging in the Dirt
If you're like me, you're happier digging in the dirt, uh, I mean soil, than doing just about anything else. If you have garden stories, especially iris stories to share, please let me know. I would love to hear them.
Thank you for visiting my irises and me. I hope you enjoyed the article, and maybe learned a bit about this lovely, exotic-looking flower.
Questions & Answers
I have a 5-year-old bearded iris bed and great greens but they have never flowered. What can I do?
By "great greens" do you mean great leaves? If they are not blooming, it could be that they are planted too deeply. It could also be they are not getting enough sun. Irises are sun-loving plants and need at least 6 hours of sun per day.Helpful 24
I have transplanted irises into places they are not getting enough sun. It is the end of May would it be OK to move the plants in too much shade right now? l did not know you should not mulch directly on top of the rhizomes.
The best time to move them is July through September, but if you live in the deep south, you can move them most anytime, assuming a mild winter. Be aware that if you move them in late winter or early spring, they probably won't bloom until the following year.Helpful 4
Which way do you orient the iris' rhizome so that the flower faces outward?
Because iris flowers are the same all the way around, they don't face any particular direction. However, the rhizomes get longer and longer, seeming to creep across the soil as they grow, so I would suggest putting the end with the leaves facing an area that will give them space to grow across the planting bed. If you have plenty of space, it doesn't matter which way they face.Helpful 12
My mother used to cut off the leaves about 8 inches up when she transplanted iris. I think that was to off-set the root shock. What do you, the writer of this article, recommend, should I cut my irises' leaves or leave them long?
What she did is called fanning the iris. When cut like that, they look like an unfolded fan. It's done in the late spring or summer after they have bloomed. It makes transplanting easier, as removing the weight of the long sword-like leaves helps the plants remain stable until the roots have time to become re-established. I do recommend fanning them when transplanting, as well as every year after bloom season.Helpful 11
I’ve recently dug up my father’s very neglected iris garden. Many single irises have very long rhizomes. He said to just cut them in half. I see in your picture that you seem to have done the same. How do I know if there is a good cutting point?
You can cut or break off the pups at the point where they are attached to the "mother plant". If you cut them, be sure to use a clean, sharp knife WITHOUT a serrated edge. Some of the older ones may appear shriveled or have rows of tiny holes in them. The shriveled ones have some rot. The little holes are from iris borers. Put either of these in the trash. Don't compost them. I have been known to cut off the shriveled parts, then plant the remaining part. If you do this, wash the knife very well before using it on additional rhizomes to avoid spreading disease to other plants.Helpful 9
© 2012 MariaMontgomery