I'm no expert, but when our bearded iris bloom in the spring, they need to be watered at least a couple of times a week, more if the weather gets hot real fast. After they bloom, the foliage stays green until about now--I've noticed iit's dying back. We're located in the high desert west, where it is hotter than blazes in the summer, and then winter lasts about six months!

IU guess this brings up the issue that drought means differrent things to different people. The guy in Virginia is worried that his tulip trees are diying. They never could live where I live, even on a wet year. In Central Tx, Irises are drought tolerant but if they don't get there winter and spring rains they do not bloom, but they do not die either. Our drought tolerant wildflowers don't bloom without spring and fall rains, but they don't die. They react by staying dormant. Actually this last spring was the first year my irises did not bloom in 25 years. I do not water. I guess I am somewhere between the virginian and the high plans guy. I just got some iris from an abandoned homestead that have been alive for a long time. I wouldn't rate them as a cactus companion though.

Here in S. Oregon, we get a fair amount of rain into summer, but then it tends to be pretty dry far into fall. But bearded iris around here tend to do fine on their own when neglected. They may bloom less, if at all, but still survive. Same with some daffodils I've seen around as well, but they tend to start looking worse earlier on.

I, also live in the high desert on the eastern side of the Sierras. I have about 75 bearded iris that have bloomed every year since I moved here 3 years ago. Yes, they are drought tolerant but that doesn't mean no water at all. They require little water in the winter but as spring approaches it's time to water. My drip system then waters them for a half hour three times a week. Once blooming has finished like now they're content with water once a week, the same amount. Since I have rebloomers I increase the water back to the 3 times a week about the end of August and by the time the temps are dropping my iris will bud for fall blooming. Too much water is bad for iris. I've had divisions stay out of soil and water for months and they don't die....they go dormant.

Yes, I water my irises every couple of days in July and August - it's 115 F here so they need a little help, but in the winter sometimes not for weeks - and even in the freezing cold of January sometimes they bloom - go figure.

Old fashioned bearded Iris, are said to be drought tolerant.
I would say Old in this case would mean varieties bred before 1920, or from parents that were bred before that date.
Old Iris cultivars are much closer genetically to wild plants that had need to develop traits to survive where there was unreliable rainfall in their native environment.
I intend to add a few Old Fashioned Iris to my Old Rose Garden.

Lux.