I'd wait until they're at least done blooming. Fall is better.
Leslie

I'm no expert, but I have to say July is better than fallÂin cold climates it's important to give the roots enough time to get established before frosts and freezes set in.

However, my information relates to Tall Bearded Iris; perhaps Grammhony's advice is better for your Japanese Iris.

I don't know about the ones you have I have the tall ones also and my neighbors dug a bunch of mine up in like July and they are doing great.....Stacy

I don't think they will bloom if you move them now. But, you never know if you don't try.

Best would be to wait till after the flowers are gone.

Moni

alisande, your probably right in saying July. I was thinking more of September, when it wasn't so hot, but before the night time temps drop to low.
Leslie

I think it may depend on where you live. If you live in Canada, July may be better. Here in the deep South, I think fall is better.

Thank you ladies, I think I will do it in July, as I do live in Canada.

I read a lot of the Garden Web posts. Most people wait and move spring-bloomers in the fall, when they are dormant. Any time I moved or planted something in June or July ,it died, from the heat I guess.

May just be an ol' country tale but momma told me when iris are moved, they don't bloom the first year. It turned out true as she said whenever I got iris from her.
Lynn

Lynn, that was the experience I had. I moved some from my MIL's yard after she died. But! the next year they were spectacular!

I have moved mine several times and at various times of the year. Just make sure you keep as much soil attached as possible and water for a few days. They should be fine. I move flowers around all the time. Never have a problem.

You can also divide them. Prior to digging them up, use a long, sharp knife to cut through the roots, then a sharp spade to slice the cut to the bottom of the roots. Once sliced through, dig them up and fill in the hole with dirt. This way you can keep some in one spot and move some to another spot. The removed area will fill in nicely in a few years time.