From the perspective of the Paeonia lactiflora plant, winter is not a period of death but a crucial phase of dormancy. This dormancy is a survival strategy, triggered by shorter day lengths and cooler temperatures. The plant's growth hormones shift; those promoting top growth (like auxins) decrease, while resources are redirected downward. The plant's sole objective is to protect its crown (the base of the plant where all growth buds emerge) and its storage roots. These organs are the lifeline, containing all the energy and genetic blueprints needed to burst forth with new growth in spring. Preparing the plant for winter means facilitating this natural process and shielding these vital parts from extreme conditions.
As photosynthesis slows in autumn, the plant begins the critical work of storing carbohydrates in its thick, fleshy roots. Your role is to support this process. Continue to water the peony deeply if autumn is dry, as the roots are still active and require moisture to absorb remaining nutrients and convert them into stored energy. Do not fertilize with high-nitrogen fertilizers, as this can spur tender new growth that will be killed by frost, wasting the plant's energy. Instead, a light application of a low-nitrogen, high-potassium fertilizer or a top dressing of compost can provide beneficial micronutrients that strengthen the root system without forcing new shoot growth.
After the first hard frost has blackened the foliage, it is time to remove it. This is a vital sanitary practice from the plant's viewpoint. The dead leaves and stems can harbor fungal spores, such as those causing botrytis blight, which would otherwise overwinter right at the crown and infect the new spring shoots. Cut the stems down to within 2-3 inches of the ground. Remove all this debris from the garden entirely—do not compost it, as most home compost piles do not get hot enough to kill these persistent pathogens. This cleanup gives the plant a clean, healthy start for its dormancy.
While mature, established peonies are extremely cold-hardy, a protective layer of mulch is insurance against unpredictable winter temperature swings. The primary threat is not consistent cold, but alternating cycles of freeze and thaw. These cycles can cause the soil to expand and contract, which can "heave" the plant's shallow crown out of the ground, exposing it to drying winds and freezing temperatures. After the ground has frozen hard, apply a loose, breathable layer of mulch (such as straw, shredded leaves, or pine boughs) about 2-4 inches deep over the crown. This layer acts as an insulator, keeping the soil consistently cold and preventing heaving. It is crucial to apply mulch after the ground freezes; applying it too early can create a damp, warm habitat for rodents and rot.
As winter wanes and daytime temperatures become consistently above freezing, the plant will begin to sense it is time to break dormancy. Once the threat of hard freezes has passed and you see small, red buds (called "eyes") beginning to swell at the crown, carefully remove the winter mulch. This allows the soil to warm up, signaling the plant that it is safe to initiate its spectacular spring growth. Leaving the mulch on too long can delay growth and promote rot in the newly awakened buds.
