Herbaceous peonies are garden plants known for their large, often fragrant blooms and lush foliage. Unlike tree peonies, which develop woody stems that persist above ground year-round, herbaceous varieties die back to the soil surface each autumn. This growth habit is important for their successful cultivation.
Planting Herbaceous Peonies
The best time to plant herbaceous peonies is during the fall, from late September through October, before the ground freezes. This allows the root system to establish before winter. Proper site selection is important for these long-lived plants, which can thrive for decades. They require a minimum of six hours of direct sunlight daily for abundant flowers and robust growth.
Well-draining soil is essential for successful peony cultivation. Heavy, waterlogged soils can lead to root rot and poor performance. Amending the planting site with organic matter, such as compost, improves soil structure and drainage, creating an ideal environment for root development. This preparation helps ensure the plant’s long-term health and flowering capability.
Planting depth is a key factor determining whether an herbaceous peony will bloom. The “eyes,” small, reddish growth buds on the root crown, must be positioned no more than two inches below the soil surface. Planting deeper than two inches often results in healthy foliage but few or no flowers. This precise depth allows the plant to receive necessary chilling hours for flower bud formation.
Ongoing Care During the Growing Season
Once established, herbaceous peonies benefit from consistent, but not excessive, watering, especially during dry periods. Deep, infrequent watering is preferable to shallow, frequent applications, as it encourages roots to grow deeper, making the plant more resilient. Providing approximately one inch of water per week, from rainfall or irrigation, is sufficient.
Applying a low-nitrogen fertilizer in early spring as new shoots emerge can support vigorous growth and flowering. Fertilizers with higher phosphorus and potassium, such as a 5-10-10 or 5-10-5 formulation, are recommended. High-nitrogen fertilizers should be avoided, as they can promote excessive leafy growth at the expense of flowers and may lead to weaker stems.
Many herbaceous peony varieties produce large, heavy blooms that can bend or break stems, especially after rain. Providing support for these flowers is often necessary to prevent them from sprawling on the ground. Peony rings, which are circular supports with legs, or individual stakes, should be placed around the plant early in the growing season. Installing these supports when the plant is relatively small allows the foliage to grow up through the structure, concealing it and providing discreet support for the developing flower heads.
Common Pests and Diseases
Ants are often seen crawling on peony buds. These ants are harmless to the plant and are simply attracted to the sugary nectar secreted by the developing flower buds. They do not damage the flowers or foliage and do not need to be controlled. The ants depart once the flowers open.
Botrytis blight is a common fungal disease that can affect herbaceous peonies, particularly during cool, wet spring conditions. Symptoms include blackening buds that fail to open, brown spots on leaves, and stem rot near the soil line. Prevention involves ensuring good air circulation around the plants and thorough fall cleanup of all plant debris. Removing infected parts promptly can also help limit the spread of the disease.
Powdery mildew can appear on peony foliage later in the growing season, especially in humid conditions. This fungal disease manifests as a white, powdery coating on the leaves. While it can make the foliage appear unsightly, powdery mildew is a cosmetic issue for peonies. It does not cause significant long-term harm to the plant’s health or future flowering.
Fall and Winter Preparation
As autumn progresses and the first hard frost arrives, herbaceous peony foliage will turn brown or black, signaling the end of their growing season. Cut the stems down to about one inch above the ground. This tidies the garden bed and prepares the plant for dormancy.
Removing all cut foliage and any fallen leaves from around the base of the plant is an important step in disease prevention. Fungal spores, such as those causing botrytis blight, can overwinter on plant debris. Clearing the area helps reduce the inoculum for the following spring, promoting healthier new growth.
In most temperate climates, established herbaceous peonies are hardy and do not require additional winter mulch. The plant’s root system is robust enough to withstand winter temperatures without extra protection. Applying mulch where it is not needed can sometimes retain too much moisture around the crown, which might be detrimental.