The peony is a beloved garden plant, renowned for its large, fragrant blooms that signal the arrival of late spring and early summer. Gardeners often receive a bare root division, which is sometimes incorrectly called a “peony bulb.” This common misclassification leads to confusion about how to properly plant and care for the perennial. Understanding the true structure of the peony’s underground system is the foundation for successfully growing this long-lived flower and ensuring it produces its spectacular display.
Peony Anatomy The Crown and Tuberous Roots
The underground structure of a peony is not a single, self-contained bulb but a complex perennial root system composed of a crown and tuberous storage roots. The crown is the central, thickened area where the stem meets the root mass, and it serves as the plant’s permanent growing point. This crown is where the plant tissue transitions from root to shoot, and new growth emerges from the crown each spring.
Attached to this crown are large, fleshy storage units known as tuberous roots, which are modified lateral roots that store starches and nutrients. These roots sustain the plant through its dormant period, providing the energy reserves needed for the massive burst of growth and bloom in the following season.
The most important feature on the crown are the “eyes,” which are small, dormant, reddish-pink buds. These eyes are the beginnings of the next season’s stems, leaves, and flowers. A healthy bare root division should possess at least three to five of these buds, as proper growth and blooming depend on their precise positioning during planting.
Why Peonies Are Not True Bulbs
Peonies are classified as herbaceous perennials that grow from a root system, and are not considered true bulbs in the botanical sense. A true bulb, such as a tulip, daffodil, or onion, is a modified stem with a basal plate and layers of fleshy, modified leaves (scales) wrapped around a central shoot. The entire food supply and embryonic flower are contained within these layers, often protected by a papery outer layer called a tunic.
In contrast, the peony’s structure is a crown with tuberous roots, where the storage function is performed by the enlarged roots, not by modified leaves. This fundamental difference in anatomy means peonies do not go through the same life cycle as a true bulb, which is essentially a complete, self-contained miniature plant awaiting activation. The peony crown and its attached roots form a permanent, expanding perennial mass that must remain in the ground.
The correct botanical term for the peony’s underground storage mechanism is a geophyte with tuberous roots. The distinction is important because the planting and care requirements for a root-based perennial differ significantly from those for a layered, self-sufficient bulb. Treating a peony like a deep-planted tulip bulb is one of the most common mistakes leading to a lack of flowers.
Planting Peony Roots for Success
Successful peony cultivation hinges on proper planting, which relates directly to the structure of the crown and eyes. The timing is important, with fall planting, approximately six weeks before the first hard freeze, being generally considered the best window for establishing the roots. This allows the plant to develop a strong root system while dormant, minimizing transplant shock.
The most critical factor in planting is the depth of the eyes below the soil surface. For most herbaceous peonies, the eyes should be positioned shallowly, no more than one to two inches below the soil line. Planting the crown any deeper than two inches is the leading cause of a peony failing to bloom, a frustrating condition known as “blindness.”
Gardeners in warmer climates, such as Zone 8, should aim for the eyes to be closer to one inch deep to ensure they receive enough of the winter chilling necessary to initiate flowering. Regardless of climate, the planting location should offer at least six hours of full sun daily and have excellent drainage, as peonies dislike sitting in soggy soil. A well-prepared hole that is 12 to 18 inches deep and wide, amended with compost, will provide the fibrous roots the space they need to spread and support the long life of the plant.