I have mine planted in just pea gravel in an 8" x 8" basket so I won't have to replant them for awhile. I don't fertilize them as I have been told they are very good at sucking excess nutrients out of the water and that's what I want them to do :-) So far so good, itty bitty stub of 3 leaves is now up to 6 much taller ones and it's only been a few weeks!

Hi boulder, mine kept getting blown over (they're top heavy)so I planted them in gravel in a plastic feed pan (about the size of an oil pan but the feed pans were cheaper). The wider pots don't tip over. My first iris were 3 little plants from the exchange here and they outgrew their 8" pot the first summer. Mine are sitting with about 1-2" of water over the rim of the pot.

A few years ago I dug a bunch of water iris from the wild and tried several planting techniques to see which would work out best.
I planted some barefoot in the rocks, just washed off the roots and stuck them in between the rocks. Some in full sun and some in part shade. At the same time I planted some in a lily style pot with soil and fertilized them.
Three years later here is what I found; the ones planted barefoot in the rocks in full sun have survived ok, but almost no blooms and have not really grown much. They do however continue come up each spring and add greenery to the rocky shore area which is good, but I wouldn't exactly say they are thriving.
The ones I planted barefoot in the rocks in part shade have produced very nice foliage and have grown considerably, but have not yet bloomed. Again this is ok as the greenery looks nice and really that's fine with me.
The ones I planted in soil in the lily pot and fertilized have almost outgrown the pot, they bloom as much as they ones did in the wild area where I found them.
Anyway, that's my experience with them, take from it what you want.
You can see some pictures of them by clicking here.

Mucky waters, are those red petunias growing in the water? Your pond is lovely.

I have my yellow flag iris planted in a 20" wide pot that is about 12" deep. They are planted in all clay topped with pea gravel. They are exploding out of their pot with many plants growing with their roots free and the main plants still stuck in the pot. They were originally planted with Iris versicolor (blue flag) but the yellow flag muscled out the blue. I cut off all the dead blooms off before they seed since the yellow flag is invasive.

I grow all other water loving iris outside the pond. Lousiana iris grow like the dickens!

Hoku the petunias are planted in a container sitting on the edge of the pond. They are actually some of my son's flowers that he planted and has been taking care of himself.

I have another question about water iris. I planted some this spring that I put in some lily pots. When should I expect them to bloom? This year or next? They are growing fine and putting on a lot of new growth.

That is one of the most beautiful ponds I have ever seen thanks for sharing those great pics! I'm jealous.. :-)