I don't know either but if they have spots like mine do, I wouldn't. If the leaves were clear, I don't know why not. Do you have that many?

i have not seen spots on mine. had a large area maybe 4x15 ft that i told dh he could mow off as they were mostly dying. now there are lots of dead leaves just laying there. and lookiing for mulch for my turnips I wondered if I could use the iris leaves.

Do it as an experiment. Pretty soon the fall leaves will be available. Those chopped with a lawn mower make a pretty mulch.

There's a borer that overwinters in the leaves so they say to discard foliage. I've never gotten borers in my iris and don't know if they can also affect other plants. I do get brown spots on the leaves which doesn't seem to do much harm except for making them look bad. I'm going to try cutting mine back this fall and trashing all the leaves to see if they will look healthier next year. I've got to do that with my phlox too since some of those had phlox bugs which also winter over in foliage.

I haven't priced straw lately. I bet it's high and maybe hard to find.

I use them, qumum -- it's time for me to cut my iris back to fans and I cut up all those fronds and put them in the compost bin as greens. I also get a ton of daylily brown fronds every summer (browns) which I cut up, as well. I don't know why you couldn't use old iris leaves and daylily foilage for mulch. Lots of old foilage on the many daffodils in the spring, as I let them die down and brown off, tied in bunches with rubber bands. They would make great mulch if you cut them up a bit.
Sunny

I'm with Christie on this one. I have problems with leaf disease on some iris so I wouldn't use them. I never use old tomato vines either for the same reason.

I've used iris, daffodil, tomato vines, and anything else I had available. I've never had a disease that caused any real damage. But that's me. I don't know about your place. ;)