Japanese Irises: Dispelling the Prima Donna Myth

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Posted by @PollyK on
Some of my customers see the pictures of lovely Japanese irises on my website and say, "I wish I could grow some of those; they're so beautiful but so hard to grow." Are Japanese irises really that touchy? No, I don't think so.

It seems that everyone who sees the Japanese iris wants to try growing one. That's understandable; they are huge, fluffy and beautifully soft colored. So many people believe they are hard to grow; in fact, one of the people in my local iris society has run a nursery for many, many years. He sells irises, yet he believed they could only be grown in Central NY.

Let's talk about what's true and what's not true with Japanese irises; here are some questions I've been asked.


They're only hardy to zone 6, right?

No. It's widely documented that Japanese irises are hardy and thrive to zone 4. All the major growers, including Ensata Gardens, list them as being hardy to zone 4.

On the Japanese iris robin, where Japanese iris lovers talk, I mentioned this discrepancy in zones.  Many Japanese iris lovers verified they are grown widely in zone 4.

I believe they could encounter a problem in zone 3, but it depends to a large extent on how much snow goes along with the cold. If you live in zone 3 and have significant snow cover, it seems they do well. In the Northern Plains there are some losses. We are currently trialing some Japanese in zone 3, and will let you know the results but for now you can trust Japanese irises to grow solidly in zone 4.


They need gallons of water to grow well.

This is partially true. Do they need to be standing in water? Absolutely not! This idea was perpetuated by pictures of the beautiful iris beds in Japan, showing Japanese irises standing in flooded areas. It was a lovely picture, but that's all it was. At bloom time, the irises were deliberately flooded since it made for such a lovely photographic scene. Japanese irises, in fact, will not survive the winter under standing water in the colder zones.

Japanese irises do need water but one inch per week is sufficient. Bloom size is influenced by the amount of water they get. If they receive less than one inch of water a week, they will still bloom but the blooms will not be the gorgeous 6-8 inch size they are noted for.

Most garden beds and borders get enough water for Japanese irises to grow well. A heavy mulch will help conserve moisture.

I would not recommend trying them in the desert but for most parts of the country, water is sufficient to grow Japanese irises.


They need acidic soil, so they can't be grown outside of the Northeast.

This is absolutely not true; what they don't like is alkaline soil. Does that seem to be a contradiction? No, most people's soils are acidic to neutral; very few people actually have alkaline soil.  A PH of 7 is considered neutral and Japanese irises will take a PH of 5-7; that covers almost everyone in the US. In strongly acidic soil, below a PH of 5, Japanese irises do not perform as well.

I have customers successfully growing Japanese irises from California to Alaska and from Alabama to Maine, including all places in between.

If the leaves on your Japanese irises are yellowing, that's an indication of a PH that's too high. It's an easy fix; apply Miracid every two weeks and then put down some agricultural sulphur, that's all you need to do.  In most instances this type of fix will never be needed.


Japanese irises are heavy feeders, needing a lot of fertilizer.

The first answer is yes; the second is no. Japanese irises are very heavy feeders but two applications of 10-10-10 (or equivalent), one in the spring and the other just before bloom will satisfy their needs. If you want really huge blooms, the plants will appreciate some composted manure around them.


Japanese irises need to be divided every three years; they poison the soil and cannot be replanted in the same spot.

The jury is still out on that one. Personally I have had Japanese irises grown in the same spot without dividing. Some information advocates the need for dividing irises regularly, others differ in that opinion.  If you would like to add them to other areas of your garden, they are easily divided in spring and early fall.

I have never seen indications of Japanese irises poisoning the soil; I would still like more information on this before making a decision.


Seven-year-old granddaughters love to pick Japanese irises just as they open, using them for doll dresses and wearing them behind their ears.  Of course this always happens before you get a good picture for your website. 

(Chuckle). OK, you got me on that one.

Now you know how easy it is to grow Japanese irises; it's time to give one a try. Be sure you buy yours from a grower, it's important to ensure you're getting the pretty Japanese iris you admired and paid for, not a no-name Japanese iris from some of the big retail houses.



Comments and Discussion
Thread Title Last Reply Replies
Japanese iris and Siberian iris by masonbee Apr 21, 2018 7:44 PM 1
A really informative article... by Sharon Apr 2, 2010 9:10 AM 14

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