I'm above 6500' and bearded irises do fine here. Some are more vigorous than others, but in general, if they get full sun and some irrigation, they do fine. Could there be some disease that are getting yours? Or insects like borers? You can dig a failing one up and see what is going on with the roots, and post photos here for opinions, and you can call the county extension for ideas as well. Good luck!

Hi Niciole, I grow bearded irises in Elizabeth CO, 6700 ft. Also wanted to mention that there are a couple of iris societies in CO, I belong to one based in Co Springs called the Elmohr Iris Society. There's also the Mountains and Plains Society in Denver area, I'd reach out to whichever of those is closest to you for specific advice. Both groups are also on FB.

I'm wondering if putting Preen down, a weed preventer may be stunting their growth?

Since the failing is happening in the second year, it sounds like iris borer. Read up on that pest.

I looked up Iris borer. Could be. I see a LOT of little rhizomes...could be only the miniature iris are coming back too. They are hardier. My neighbor across the street spent some serious money on Schrieners Iris.....they have ALL disappeared......but the huge plot of miniature iris she has are going strong.