Pruning peonies is a garden chore many overlook. Because peonies are herbaceous perennials, meaning that they die back completely in fall and produce entirely new shoots in spring, they do not require pruning in the sense that woody plants do; that is, to encourage new growth and maintain shape. That doesn’t mean that you should put the garden shears away, however: by pruning peonies at the proper time and in the proper way, you can ensure a healthy and productive plant year after year.
To encourage the biggest blooms, some gardeners engage in a practice called “disbudding.” Some peony stems will produce more than one bud. When this happens, leave the main bud intact, but remove any smaller side buds before they bloom. This will allow the plant to put all of its energy into one large, healthy bloom rather than two smaller ones.
After blooming, remove spent flowers to prevent seed production, which saps energy from the plant. Cut just below the flower, leaving as much foliage as possible. Plants use their leaves to make food, so the more leaves left on the plant, the more food it can make for next year’s blooms. Peonies make spectacular floral arrangements, but try to resist cutting more than one third to one half of the flowers as this, too, will detract from the following year’s flower production.
Summer and Fall
Peonies are very sensitive to excess moisture, particularly in the summer. Heavy rains, high humidity, and excess heat can encourage numerous fungal diseases such as botrytis, phytophthora, and sclerotinia. Remove any affected areas as soon as you see them and dispose of them in the garbage, not the compost bin. Cut away all stems in fall and remove the mulch as well, so that fungal spores can’t overwinter. Clear away all clippings and dispose of them. Be sure to sterilize your pruners after each cut so as not to spread any disease.