Divide Native Irises In November and December

Regular readers may recall my Great Iris Dilemma. Basically, I need to get rid of my nursery-bought Iris douglasiana, because I'm propagating local native irises, and they hybridize easily.

Fortunately, last week was the monthly session of the local CNPS propagation group, and guess what: we were dividing iris. I got some takers for my Iris douglasiana! They will come and help me dig them and give them excellent new homes! I am very grateful, and can now let these plants go without guilt!

When I was new to gardening, and needed to divide my Douglas iris plants, I Googled: "when to divide irises," and came up with "July." I divided in July. They died. Don't do this.

The bearded iris varieties have different maintenance requirements than our natives. Divide native iris in late November or early December (December in Southern California). The general rules are:
  • Divide your native irises every three to five years, in November or early December.
  • Dig em up, and pull them into separate rhizomes (that's the tuberous part that grows along or just under the ground), or small clumps of two or three rhizomes.
  • Replant them as soon as possible. Don't let the roots dry out.
  • Plant so the rhizome lies along the ground, so the top of the rhizome is still visible. Don't bury them.
Irises are easy to care for. The Society for Pacific Coast Native Iris has a good page on Iris care here. You can water them year round. They like a bit of leaf mold. They will tolerate sun near the coast, and need some shade inland. You can tidy them up by removing dead leaves. You'll enjoy blooms often as early as January. Mine don't bloom for very long, but they are in the shade much of the day.

The irises we were dividing last weekend had lingered too long in pots. Basically they were leftovers from the last native plant sale.

After we hacked and smashed them apart into big clumps - which was hard work - a volunteer rinsed them off. Rinsing is advised because in pots, they can harbor harmful bacteria and other organisms. It's best to give them a fresh start.

Below you can see a nice and clean clump. Your planted iris may not have such long white roots. The new roots should be a couple inches long at least.

In the photo above, you can see that the growth will be in the direction of the person's hand. The next photo shows this more clearly - the direction of growth in the shot below is away from the person's hand:

If you are planting iris in a pot, be sure to allow for it to spread in the direction of growth. Plant the non-growth end near the side of the pot. Don't try to plant them in the middle of the pot, and don't try to plant them so the leaves are upright.

Do be sure, however, that the white roots are all under the soil. It's OK for the leaves to be at an angle, if that's what it takes to get the white roots buried. And keep the top of the rhizome slightly above ground, level with the ground. Or anyway not buried. I'm not exactly sure how far apart to plant them - use your judgment to give them some breathing room, but plant them close enough that they will make a mass display when they fill in. Or you can plant them in smaller groups, in a meadow planting, for example.

The volunteers worked happily together for a couple of hours and got a tremendous number of potted irises divided and repotted. I hope they will sell well at the next CNPS plant sale.

And off they go, to the protected environment of the nursery's shade house, to grow and thrive.


Susan Krzywicki said…
Thank you so much for this post. The most cogent and comprehensive "from experience" post I've seen. I am just about to install native irises in a garden and so this is very timely.

I love thinking about the global issues of hybridization, gene pools as well as learning the practical, hands-on knowledge you have shared.
Christine said…
Perfect timing! I'm just about to attempt this myself and hadn't gotten much further than "don't do it in the summer."
A good reminder for us. We have some native iris that are at the base of a slope and need to be moved, to make way for a small retaining wall behind our future greenhouse. I'd potted a few in early spring, as an experiment, which I've managed to keep alive, but the rest just need to be relocated and now seems like the perfect time. I'm glad you managed to successfully re-home your I. douglasiana!
Country Mouse said…
I'm glad this post was useful and timely! Thanks for coming by.
Phooey. I really need to move my iris right now. I wonder if I'll kill them.
Town Mouse said…
Lisa, I strongly recommend that you wait - it works so well when done at the right time. But maybe if you add water to your divisions it will work out? Good luck!
tierramor said…
Does anyone have a good source doc for which Ca genuses are more likely to hybridize? With so many cultivars and varietals out there being sold, it seems almost an impossible task to guide clients towards local natives, would be easier if there were a couple most dangerous species to focus on in terms of avoiding the loss of micro-adaptations in local gene pools.
Country Mouse said…
Hi Tierramor, I'm glad you are concerned for the local gene pools. Your best bet is to shop at CNPS plant sales. Or if you are lucky enough to have a restoration nursery near you - go there.

At our sale, (Santa Cruz County CNPS), we do buy in some irises as they are so popular. But we also grow some that are local selections. Also at California Native Plant Society sales (and restoration nurseries), the volunteers are knowledgeable and can tell you which are from a specific watershed.

As far as I know all irises will hybridize. I don't know of any that are more or less apt to have a fling with a neighboring species or variety! And hybridization happens in nature too - I believe I may have seen a hybrid of I. fernaldii and I. douglasiana. But only one, and not personally - it was a photo taken in a local state park.

Getting information about likelihood to hybridize - for any species - is very difficult - nay, impossible - because the facts are just not available. There is anecdotal evidence but actual research dollars are not there for this effort - that's what I've been told when trying myself to find out. So I try to just propagate local species and plant completely different things than grow natively around me, if I want more variety. Like seaside daisy - not growing wild at 900 feet! and six miles inland!