Wow. Are you lucky. I know there are early, mid and late peonies ~ same as bearded iris. The few pics I've seen with both never id the peony.

So I'm not much help but I do think the iris foliage would block the peony. Iris in back or beside would be my vote.

I guess it depends on how big the peonies are, whether you use rings to hold them up, and how tall the iris can get. I've got both, but not together. If you pick the right sized iris, you should be okay. Unfortunately, the sizes listed for most iris are more guidelines rather than exact measurements, and the actual height will vary due to climate, soil conditions, etc., as well as the cultivar in question. All things being equal, I'd go for early blooming intermediate iris in front of the peonies. Most of my iris bloomed about 2 weeks before my first peony opened up, and all but one were done before my last one opened up. The iris foliage in full sun doesn't get anywhere near as high as the peony flowers (with double rings, not the wimpy single ones), so if your iris are done blooming before the peonies start to open, you can deadhead them and be fine. Of course, the iris foliage will block a lot of the peony foliage, so if you prefer the dark green of the peonies to the light green of iris, this won't work out for you.

I do not believe you will get iris to grow in a peony bed. I have 15 iris in a peony bed much like the plan you invision. After 4 years the iris still only sporatically bloom and increase is at a bare minimum. I suggest that if you do this you plant the iris beyond the outside edge of the peony roots. Being they are heavy feeders I feel they soak up to many nutients for the iris to survive.
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