My common Peonies — aka herbaceous or Paeonia lactiflora — always start having leaf problems once the flowers are over. I trim out browning and sick-looking foliage all summer long. Once autumn arrives, they go seriously downhill as you can see from the photo below. Usually my woodland Peonies continue to look good but all of our rain in August and September have them looking the worse for wear as well.
That is not the case with my Itoh or intersectional Peony, "Border Charm." The foliage is as lush and clean in mid-October as it was in June! Maybe it's because this plant is growing under a Ginkgo tree and doesn't get quite as much rain.
But I think it's the result of its Tree Peony parentage. Intersectional Peonies are a cross between tree and herbaceous Peony types.
Take a look at the foliage on my Tree Peony below. Equally great looking. Yes, it's also growing under a tree, but I think it's genes rather than a leafy umbrella that makes all the difference. It's especially nice to have these shrubby plants with green leaves at this season when everything else is starting to turn color. Eventually these will get bronzy, too. But it doesn't look like that's about to happen any time soon.