Peonies are cherished perennial garden plants that are famously low-maintenance once established. Their successful growth hinges almost entirely on the initial planting process. For gardeners planting bare-root peony divisions, getting the depth correct is the most significant factor determining whether the plant will produce its signature blooms. Precise placement ensures the plant receives the environmental signals necessary for flower bud development.
Distinguishing Peony Types for Planting
Understanding the specific type of peony you are planting is necessary because depth requirements differ substantially between varieties. Herbaceous peonies, the most common bare-root variety, die back to the ground each winter. Tree peonies develop woody, permanent stems that remain above ground and are frequently sold as grafted plants. Intersectional peonies (Itoh hybrids) combine features of both, possessing large flowers but dying down like herbaceous varieties. Planting instructions for herbaceous and Itoh peonies focus on the placement of growth buds, while tree peonies require attention to the graft union.
The Crucial Planting Depth
For herbaceous peonies, the focus is the placement of the “eyes,” which are the small, pink or reddish buds found on the crown of the root division. These buds are the growth points for the coming year’s stems and must be positioned extremely close to the soil surface. The general rule is that the eyes should be covered by no more than 1 to 2 inches of soil after planting and firming.
The exact depth depends on your local climate and hardiness zone. Gardeners in colder regions (Zones 3-5) should aim for the deeper end, closer to 2 inches, to provide extra protection from harsh winter weather and frost heave. In contrast, those gardening in warmer climates (Zones 7-8) should plant much shallower, sometimes covering the eyes with only a half-inch to 1 inch of soil. This shallower depth is necessary because the eyes require a period of chilling to initiate flower production, and planting them closer to the surface helps them receive the cold exposure they need.
When planting a grafted tree peony, the instruction is the reverse: the plant must be set deeply into the ground. The swollen area where the woody scion meets the herbaceous rootstock is called the graft union. This union should be buried approximately 4 to 6 inches below the soil line. This deep planting encourages the tree peony portion of the plant to develop its own independent root system, which strengthens the plant and prevents the herbaceous rootstock from growing unwanted suckers.
Preparing the Planting Site
Before placing the root division in the ground, the planting site needs careful preparation to ensure the peony’s longevity. Peonies thrive best when situated in a location that receives full sun, meaning at least six hours of direct sunlight daily. In extremely hot climates, some afternoon shade can be beneficial to prevent the blooms from scorching and to extend the flower life.
The soil must be rich in organic matter and offer excellent drainage. Peony roots will rot quickly if they sit in waterlogged soil, so heavy clay may need to be amended with compost or other materials to improve its texture. Dig a planting hole that is about twice as wide as the root mass to allow the roots to spread easily into the surrounding, loosened soil.
Proper spacing is also important, as mature peonies can be substantial plants; they should be planted 3 to 4 feet apart to ensure good air circulation, which helps prevent fungal diseases. The best time to plant bare-root divisions is in the fall, typically from September to late October, giving the plant time to establish its roots before the ground freezes. If planting in spring, disturb the roots of potted plants as little as possible to minimize transplant shock.
Troubleshooting Depth-Related Issues
The most frequent problem encountered by gardeners is a peony that produces lush foliage but fails to bloom, a condition often called being “blind.” This issue is almost always a direct consequence of planting the root division too deeply, preventing the eyes from receiving the cold temperatures required for flower bud formation. If a peony has failed to flower for several years, carefully lifting and replanting it in the fall at the correct, shallower depth is the most effective solution.
Planting too shallowly presents a different set of risks, primarily that the buds will be vulnerable to drying out, freezing, or damage from foot traffic. If you notice the eyes are exposed during the first season, gently add a small amount of soil to bring the level up to the necessary 1 to 2 inches. If a plant that was previously blooming stops producing flowers, accumulating mulch or slowly settling soil may have effectively buried the eyes too deep over time. Carefully scraping away the excess soil from the crown can often resolve the problem.