Did you know that the Iris flower is named after the Greek Goddess Iris? Iris is considered the goddess of the rainbow and a messenger for the gods. How interesting! We are fortunate to have two different varieties of iris growing in our garden. First, there is a lovely dwarf Japanese roof iris (Iris tectorum). Second, is the beautiful purple Siberian Iris (hybrid between Iris sibirica and Iris sanguinea). The dwarf Japanese Iris are relatively easy to dig up and divide. While the Siberian Iris are more challenging. Therefore, this post will focus on dividing Siberian Iris.
Estimated reading time: 9 minutes
First, a few facts about Iris.
Hardiness Zones: 3-8
Plant type: Perennial
Full Sun to part shade
Season of Interest: Spring
Height: 2-4 feet
Spread: 1-2 feet
Resistant to deer, rabbits, groundhogs, and drought
Low maintenance
Why divide?
Three years ago, we planted six lovely 5-gallon containers of Siberian Iris called ‘Caesar’s Brother’. Three are on the right side of the entrance to our deck and three are on the left. During this time, they tripled in size. In fact, they grew so large and were overshadowing nearby plants. Thus, the decision to divide. In general, you will need to divide Siberian Iris every three to five years. Hints to determine when to divide include the following:
Less blooms are appearing
The center of the iris clump is bare
The iris are over-crowding other plants
The other benefit of dividing Iris is that you will have several new plants to share with family and friends!
When to divide?
For most locations, mid-summer, July through early September is a good time to lift and divide Iris. Why? Well, Iris is dormant during this time. Therefore, blooms for the following season will not be impacted. In addition, the divided iris have time to re-acclimate to the soil and establish their roots. It’s also ok to divide in early spring when new growth if first appears. However, I believe the less risky method is to divide in late summer.
Tools needed
Here are the tools that we used during the process of dividing our Siberian Iris.
Spade shovel was used to dig up the Iris clumps to be divided.
Wheelbarrow – after the Iris clump was dug up, we placed into the wheelbarrow. It was easier to clean off and divide.
Hedge sheers were used to trim the Iris prior to digging up.
Rake used to clean up around the Iris clumps.
Hose to moisten the soil prior to digging up the clump. Also, used to clean off the clump after it was dug up.
Small hand rake was useful to clearn dirt from the clump prior to washing with the hose
Saw or Hori Hori Soil Knife to break apart the clump after being dug up
Tarp was helpful to place the divided pieces of the clump (as opposed to placing on the lawn)
How to divide?
Siberian Iris can be easy or difficult to divide. In the easy case, it will be possible to divide the Iris by pulling apart the rhizomes by hand. In the difficult case, a cutting implement will be necessary. When dividing our Iris, we encountered a difficult case and had to use a saw to divide.
Now, let’s discuss the structure of a Siberian Iris. It’s helpful to understand this structure when dividing. An Iris is supported by both roots and rhizomes under the soil. A rhizome is an underground stem that grows horizontally underground and will send up new shoots of leaves. The roots anchor the plant and provide the mechanism to transfer water and nutrients throughout the plant.
Step 1 – Trim Iris leaves
Siberian Iris grows beautiful long grass-like leaf blades. It is very helpful when dividing to cut back the leaves first. Cut the leaves to within 6-12 inches from the clump. This allows the plant to focus its energy on new growth as opposed to maintaining the leaves.
Step 2 – Moisten the soil
Using a hose, moisten the soil around the base of the Iris to be divided. Moistening will ease both the digging and the lift of the existing plant.
Step 3 – Dig up the clump
Using a shovel, insert the shovel blade at the base of the plant. Once you have gone all around the base, attempt to lift the Iris. If the Iris is still stuck, then go back around the plant inserting the shovel. We found it helpful to have a tarp nearby to place the clump of lifted Iris.
Step 4 – Wash off the clump
Using the hose, wash off the soil around the rhizomes and roots of the Iris. This will make it easier to see the rhizome and do the division.
Step 5 – Divide the clump
Using your hands, see if you can divide the rhizome. If this is not possible, then a soil knife, spade, or saw may be necessary. Each rhizome piece should have several fans (fans are a collection of 3 leaves) of leaves and a good root system. If the roots do not look healthy or the rhizome is not firm, then discard the section that is not healthy.
Step 6 – Replant the divided pieces
Replant the divided pieces in an area that receives full sun, and the soil is moist.
Dig a hole that is slightly larger than the rhizome pieces to be planted. I like to plant 2-3 pieces of the divided rhizome per hole. In addition, I like to have 3 clumps of Iris planted 12-18 inches apart. In our case, we followed the same design approach of the original Iris.
Fan out the roots and place the piece in the newly dug hole.
Cover with soil. The rhizome piece should be just under the top of the soil. Tamp the soil to secure the rhizome place.
Water thoroughly.
If you have extra pieces and nowhere to plant, then place the divided pieces in containers and cover the roots and rhizome with soil. Healthy Iris should be ok for at least one month and possibly longer. Of course, its best if the newly divided Iris are planted right away.
Caring for Siberian Iris
Siberian Iris are easy to grow and care for. In the spring after the flower blooms, cut the bloom stalk. In the summer when the seed pods form, cut them off. I find the seed pods to be particularly beautiful. After I cut them, I use in dried flow arrangements or combine with silk flowers.
