yes

I think you probably could trim them a bit, but I'd be afraid you'd ruin the gracefulness of the leaves by giving them a haircut this time of year.

I leave the foliage to get a bit brown and tatty then whip it all off - the only foliage which looks well over the summer is the Dalmatian iris pallida variegata which maintains its cool freshness throughout the season. Brown and dying foliage has done its job for this year and just annoys me looking sordid. The iris don't seem to mind at all....although I pull the old leaves rather than cutting them back....when dead, they come out cleanly and easily

Several years ago I cut half of mine almost to the ground to allow other plants to show and then left the other half uncut. I made a note to check blooms the next year - absolutely no difference.

Thanks everyone! That's very helpful. I've decided to do it. Already trimmed one clump and I am very happy with how it looks.

One of the reasons I grow Siberians is for the foliage, which not only stays lovey through the summer but turns a good yellow in the fall. I wouldn't want to cut mine, even though it's such a pain to cut out the old bloom stalks.