Cleaning Up Peonies in the Yard and Garden in Fall
The leaves and stems of herbaceous (bush) peonies, including the intersectional Itoh peonies will eventually die back as the plants go dormant for the winter. The leaves will start to change colors, deteriorate; and, the stems will eventually fall to the ground and turn 'mushy'. This is natural. Peonies are perennial plants and the outer stems 'die back' each fall, with the root going dormant for the winter. New stems will emerge in the spring, producing their beautiful flowers, again.
If you haven't cut off the peony stems on herbaceous (bush) peonies yet, they are likely looking pretty raggedy. A few varieties may still have good looking foliage; but, it is just a matter of time and they will do their dormancy thing. If you have some nice looking peony foliage, you can cut it and use in floral arrangements this fall.
Cut peony stems to ground level, taking care not to cut any peony 'eyes' (buds) that may be peaking through. The little white, pink or red buds are what will produce next years' flowers.
You can cut back peony stems anytime from early fall or after the first frost. Clean them out of the garden, so they don't lie there through the winter. Dispose of them in the garbage or burn them (if allowed in your area). It's best not to compost them, as old leaves and stems may attract fungus in wet winters.