Neglected my peonies this summer and they are all mildewed and largely browned or blackened. Will cut away the completely dead stems but is it too early to cut back all the stems? Should I leave some semi-green stalks to provide nutrition/respiration for the peony before going dormant? Poor babies are 25 years old. Looking crusty. Will apply Bordeaux mix the ground once the leaves are gone... but is there value to spraying and leaving one more month (September)?