Peonies are true perennials, known for their lush, often fragrant blooms and remarkable longevity, with some specimens thriving for a century or more. They are celebrated for their large, showy flowers, making them a popular choice for ornamental gardens and as cut flowers. Successful cultivation requires understanding their specific needs, particularly concerning planting and seasonal maintenance.
Defining Peonies: Types and Characteristics
Peonies belong to the genus Paeonia and are classified into three distinct categories based on growth habit. Herbaceous peonies, such as Paeonia lactiflora, die back completely each winter, regrowing fresh stems in the spring. Tree peonies are woody shrubs that maintain a permanent structure of stems above ground, growing larger over time.
The third type is the intersectional, or Itoh, hybrid, a cross between herbaceous and tree types. Itoh peonies feature the foliage and varied colors of a tree peony but behave like herbaceous varieties, dying back to the soil line in the fall. All peonies produce large flowers, often with five or more outer guard petals. The foliage is typically deeply lobed and provides a handsome, dark green backdrop throughout the summer.
Essential Growing Requirements
Successful peony cultivation requires meeting foundational needs, particularly sunlight and soil conditions. Peonies thrive best with a minimum of six hours of direct sunlight daily; insufficient light limits flower production. The planting site must offer well-drained, fertile soil, ideally with a neutral to slightly alkaline pH (6.5 to 7.5). Peonies quickly develop root rot if left in consistently waterlogged conditions.
The most critical factor for ensuring future blooms is the planting depth. When planting bare-root divisions, the small, reddish growth buds, known as “eyes,” must be positioned shallowly. They should be covered with no more than one to two inches (2.5 to 5 cm) of soil. Planting the eyes too deeply prevents necessary exposure to winter chilling temperatures, which are required for flower bud formation.
Peony Care Beyond Planting
Once established, peonies are notably low-maintenance but benefit from specific seasonal care. Watering should be deep and infrequent, especially during dry periods, aiming for about one inch of moisture per week. Avoid overwatering or frequent shallow watering, as this encourages fungal diseases and root issues.
Fertilization should be minimal, typically a light application of a low-nitrogen fertilizer (e.g., 5-10-10 formulation) in early spring. Excessive nitrogen leads to lush foliage growth at the expense of flower production, often seen near heavily fertilized lawns. Herbaceous varieties with heavy double flowers often require staking or support hoops to prevent stems from collapsing after rain.
After flowering, spent blooms should be deadheaded by cutting the stem back to a strong set of leaves. For herbaceous and Itoh types, leave the foliage intact to gather energy until it dies back naturally in the fall after the first hard frost. Stems can then be cut down to about two inches above the ground to reduce the risk of overwintering disease spores. Tree peonies must not be cut back, as their stems are permanent and only require the removal of dead wood or light shaping.
Safety and Common Misconceptions
A common concern is the toxicity of peonies to children or pets. Peonies contain the compound paeonol, concentrated in the roots and bark, and all parts are considered mildly toxic if ingested. Consumption by humans or animals can cause symptoms of gastrointestinal distress, such as vomiting and diarrhea.
A frequent disappointment is a plant that refuses to bloom, often leading to the misconception that it is defective. The three primary reasons for a lack of flowers are improper planting depth, insufficient sunlight, or plant immaturity. Newly planted peonies, especially from bare root, often take three to five years to develop the robust root system required for a heavy display of flowers. Ensuring shallow planting and full sun are the two most actionable steps to correct blooming failures.