I have found sun versus shade has much to do with longevity of peony foliage. I have three of the same cultivar, white with red flecks and nice thick stems. One in full sun, one in 75% sun, and one in 75% shade. Full sun went first, mostly sun went second, and mostly shade was still lush and green when I cut it recently. My peonies usually develop powdery mildew when they begin to dry and wither so I cut them when they turn gray.