Peonies are long-lived garden flowers that can thrive for decades. While hardy, they are particular about their environment, and correct initial planting is crucial for success. The most important factor determining whether a perennial peony will produce large blooms is the depth at which its root is placed. Incorrect depth is the most common reason a healthy peony fails to flower for many years.
The Critical Role of Peony “Eyes”
Peony root divisions are characterized by small, reddish-pink buds known as “eyes,” which are dormant buds on the crown tissue. These structures contain the genetic blueprint for next year’s stems, leaves, and flowers. Each healthy division should have at least three to five eyes, as they represent the future growth points of the plant.
The eyes must be positioned correctly relative to the soil surface. Peonies require cold exposure, known as vernalization, to initiate flower bud formation. If the eyes are buried too deep, the insulating soil prevents them from receiving the necessary chilling temperatures. Conversely, planting them too shallowly leaves them vulnerable to drying out, freezing, or physical damage.
Precise Planting Depth Guidelines
For standard herbaceous peonies, the eyes must be planted no more than 1 to 2 inches below the soil surface. This shallow depth ensures the buds are exposed to the winter cold required for vernalization in colder climates, such as USDA Zones 2 through 7. Planting the eyes even a few inches deeper can result in a phenomenon where the plant produces healthy foliage but no blooms, creating a “blind” plant. Gardeners in warmer regions, such as Zone 8, should aim for an even shallower depth, placing the buds just a half-inch below the surface.
Planting too shallowly, where the eyes are barely covered or exposed, is also problematic. Exposed eyes can dry out rapidly or be damaged by severe freeze-thaw cycles. The precise 1- to 2-inch measurement achieves the necessary balance between exposure for chilling and protection from the elements.
Intersectional peonies, also known as Itoh hybrids, share a similar shallow planting requirement, with their crown needing to be set about 1.5 to 2 inches below the soil level. Tree peonies, which develop woody stems, are the major exception to this rule. For a grafted tree peony, the graft union—the slight bulge where the woody stem joins the herbaceous rootstock—must be positioned 4 to 6 inches below the soil line. This deep placement is necessary to encourage the woody stem to develop its own root system, leading to a more robust and self-sustaining specimen over time.
Site Preparation and Initial Planting Steps
Before planting, choose a site that receives a minimum of six hours of full sun daily. The soil must offer excellent drainage, as the roots will rot if left in standing water.
The planting hole should be dug wide and deep to comfortably accommodate the entire root mass, typically 12 to 18 inches in both directions. While the plant is set shallowly, loosening the soil beneath and around the root allows for easier establishment and downward growth. Amending the soil with organic matter, like compost, improves structure and nutrient content. Avoid adding excessive nitrogen, which encourages lush foliage growth at the expense of flower development.
Post-Planting Care for Establishment
Once the root division is placed at the correct depth with the eyes facing upward, backfill the hole with the prepared soil. Gently firm the soil around the root to eliminate any large air pockets that could cause the roots to dry out. The newly planted peony requires a thorough initial watering to settle the soil completely and bring it into full contact with the root surface.
During the first growing season, consistent moisture is important for root establishment, although peonies do not tolerate overly wet conditions. If you choose to mulch, apply only a light layer of organic material around the planting area, ensuring it is kept several inches away from the crown. Mulch piled directly over the eyes acts like extra soil, effectively planting the root too deep and hindering the vernalization process. Peonies often spend the first year or two establishing their extensive root system, so patience is required, as abundant flowering may not occur until the second or third spring after planting.