Whether you prefer bearded or non-bearded, we can all agree that irises are quite beautiful.
However, unless you’re growing them as annuals, you may also be aware that these wonderful plants occasionally get overcrowded and will need transplanting.
This also happens when you’ll want to divide your irises: getting the timing and method right is important.
When Is The Best Time For Transplanting Iris?
While some consider it safe to transplant irises at any point in the growing season, this can affect the plant’s ability to bloom.
When transplanting in warm weather after flowering ends, you’ll get better results every time.
Rhizomes vs Bulbs
Before we can get into the when and hows, the root type must be brought up.
There are 5 subspecies groups of iris, many of which were once their own genera.
Some of these plants have bulbs, and some have rhizomes.
The five subspecies are:
- Hermodactyloides (reticulated bulbs)
- Iris (rhizome)
- Nepalensis (Bulbs)
- Limniris (rhizomes)
- Scorpiris (bulbs)
- Xiphium (bulbs)
As you can see, many of these iris types have bulbs, but the 2 most common ones are both rhizomes.
It has led many gardeners to mistakenly claim that the term “bulb” is interchangeable with “rhizome” for irises.
However, the good news is that the methods are very similar for both rhizomes and bulbs.
As a result, we’ll be mainly covering the process from a rhizomatous point of view for the sake of simplicity but will specify when there’s a deviation in bulb care.
The Best Season
Bearded irises (subs. Iris) are more susceptible to fungal infections than other iris types, so you should pick a day when the temperatures are above 50° degrees Fahrenheit.
The experts recommend that you do your transplanting in late summer to early fall when the foliage begins to decline and the blooms have already passed.
The non-bearded irises (subs. Limniris) may typically be transplanted any time from spring through fall, but it’s best to do so in early spring or late August.
The root system will have time to establish before any major temperature shifts.
The bulbous irises are best done in the early fall when the foliage is dying back for the winter.
Telltale Signs It’s Time
Of course, transplanting doesn’t happen every year, and usually, irises will need to be divided every 3 to 5 years.
You can tell it’s time to divide from a few common symptoms:
One of the most common signs is when your iris isn’t flowering as well as in previous years, which will happen with both bulbous and rhizomatous plants.
In the case of many dwarf cultivars, the plant may stop blooming altogether.
Another sign among rhizomatous irises is when you can begin to see the rhizomes pushing up to the surface due to limited space underground.
Finally, a common sign with clumping species such as Siberian Iris (Iris sibirica) is when the middle of the plant begins to die, leaving an outer ring of healthy growth.
This step is generally the same for every iris plant.
Here are the tips to consider when uprooting:
- It’s best to prune back the foliage to around 2″ or 3″ inches for dwarf plants and around 6″ to 8″ inches for full-sized plants before digging the plants up so it can focus on root growth.
- Dig around the root system and use a fork to lever out the root structure.
- If you can’t extract an entire rhizome mass at once, you can divide it first, then lift each section out on its own.
- Gently clean any excess dirt off the root structure and examine it for signs of disease, such as softness or discoloration.
- You may need to cut away the infected area and sterilize it before dividing severe diseases like iris root rot.
This is where things get a little different. If you’ve bought whole garlic, you’re probably already aware that a bulb will produce smaller bulbs around it.
Here are the steps when dividing an iris plant:
- Gently break off these smaller bulbs, each becoming an iris plant.
- Squeeze the mother bulb to check for signs of softness.
- If it’s still firm, it can also be replanted.
Dividing Clumping Rhizomes
There are a few ways to divide the rhizome when you have a tight clumper, although the pie method often works best and can be done before lifting the clump out of the ground.
With this method, do the following steps:
- Cut the rhizome in straight lines as if slicing a pie using a sharp, sterile tool (a pruning saw tends to be a good choice).
- Make sure each piece has at least one healthy fan on it.
- Once you have as many slices of iris pie as you’d like, cut away the inner point of a dead or dying rhizome.
Dividing Non-Clumping Rhizomes
These can often be easier to divide, as you simply have to cut the rhizome into as many pieces as you wish, making sure to have at least one fan of healthy growth per piece.
Before replanting, give the tubers on a rhizomatous iris another health check and sterilize the cuts.
To do this, here are the steps to follow:
- Dip each piece into a solution of 1 part bleach to 9 parts water.
- Allow the pieces to air dry for a couple of days.
This helps prevent infections and allows the cut portions of the rhizome to become a little more resilient.
Finally, you’re ready to replant your divided irises.
This step is essentially the same for all irises.
Here are the following steps to do:
- First, plant the bulbs or rhizomes, making sure to space them adequately.
- Make a note of how deep they were initially planted and keep the soil level at that same height.
- Give your plants a light watering, and you’re good to go.
Note that bulbs that haven’t germinated can be stored, and you can also pot some of your divided plants for the winter.