Blue Siberian irises

Note to Self: Divide Iris Sooner, Not Later

The advice is to divide irises every three to five years. Not ten to twenty. There’s a good reason for that.

I speak here of Siberian and Algerian irises, Iris sibirica and Iris unguicularis. They form dense clumps of rhizomes which slowly spread outward, eventually developing a dead spot in the middle of the clump. Mine were impinging on other plants at their outer edges, and had the “donut hole” effect as well.

Algerian iris (Iris unguicularis)
Algerian iris (Iris unguicularis) before the donut hole formed

The recommended time to divide irises is from July through September, the hottest and driest months of the summer. Digging dense clumps of anything is hard work, and especially so when temperatures are in the 20s (70s and 80s in degrees F). Dry soil makes it even harder, which is why one is advised to water the area the day before starting a division project.

Digging up the two clumps was indeed a struggle, requiring the old jump-on-the-end-of-the-digging-fork method a few times. Extracted, the clumps seemed to expand vastly, which was somewhat disconcerting, since only a small fraction of each one was needed for replanting.

Blue Siberian irises closeup
Siberian Iris (Iris sibirica)

There aren’t many keen gardeners on my street, and I was fairly sure no one would be interested in doing soil preparation for planting irises, even when they’re free. Most people think of gardening as a springtime activity, and in early September everyone is busy with other things. So I planted an extra clump of each iris in new spots where I thought they would do well, but the majority of the excess is destined for the municipal compost facility, with all the potential buds and blooms never to be realized. Sad, but there it is.

This project has left me with the following thoughts:

  • When plants grow with such abundance how can anyone make a business of selling them? I suppose that’s why it’s necessary to develop new, “improved” varieties. Often, those new varieties fizzle out, and the gardener returns to the old reliable ones, which fortunately weren’t all dug up and pitched out in favour of the newer types. (But see below!)
  • It really is better to divide these irises more often than once every decade or two. Less of a struggle and less surplus to dispose of.
Algerian iris Iris unguicularis February 2022
Algerian Iris flower

I must admit that the day after I finished with the irises, including disposal, I spent a non-trivial sum on a plant of Libertia peregrinans, known as New Zealand Iris, which had been on my list of plants to acquire for years. Here is a description of it:

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An attractive and tough New Zealand evergreen perennial, Libertia peregrinans grows in stiff, upright clumps of orange and green striped leaves. New Zealand Iris spreads via rhizomes and grows to 1-2’ tall and wide. In the spring, sprays of fragrant white flowers rise below the leaf tips and attract pollinators. Highly adaptable to a variety of conditions, Libertia peregrinans can thrive in full sun to full shade. It will do splendidly in garden conditions with regular water, and it will also tolerate drought and desert conditions. Cold hardy to 15°F, leaves turn orange in the cold, adding winter color to the garden.

Libertia peregrinans plant in pot Sept. 2023
New Zealand iris, (Libertia peregrinans) still in its nursery pot, but soon to be planted.

It is also a member of the iris family, and is described as “rhizomatous.” The Latin species name, peregrinans, suggests wandering or travelling, so I suspect it will need division on a schedule similar to its iris cousins.

37 comments

        1. I apply compost made from the leaves of the trees that make gardening here a challenge, and from cut-down perennials, etc. Of course all that came from the soil in the first place, so I also add fertilizer. My soil isn’t the best–thin and sandy.

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    1. Events like that seem to happen mainly in springtime, but I will look out for opportunities to share next time. I actually bought the Algerian iris years ago from a local garden that is open to visitors. They sell divisions and extra plants to generate revenue for upkeep.

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  8. We live in an apartment and don’t have an actual garden, which is probably a good thing as we both have brown thumbs… but that means I enjoy the your gardening exploits vicariously without having to do the work! The irises are absolutely beautiful!

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    1. That’s probably the best way, Diana, because conditions vary from place to place. Mine definitely needed it after a decade or more. Irises are fairly easy to grow, but they do need sun to bloom. I have some plants that get too much shade and hardly ever produce flowers.
      You’re at a higher elevation, I seem to recall, which is why your house plants are in. I hope mine can stay out for a few more weeks.

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  10. Beautiful photos, Audrey and well done for your perseverance to separate these! Indeed it is sad how the extras are binned! One year I saw a lady planting them all along a path in the village but unfortunately, they didn’t do well.

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