In a group of plants here that started as individual plants of Paeonia lutea var. ludlowii and Paeonia delavayi, there is now a "copse" of hybrid plants some of which are now bare stems, some with brown leaves and some still with green leaves. In a mild year the green persists until spring, but usually they all eventually drop. My P. rockii has dropped its leaves but often retains it's leaf stems well into spring unless I tidy it up.