Peonies are beloved garden plants, offering spectacular flowers in spring and early summer. Successfully propagating them requires specialized methods, as simple stem cuttings are largely unsuccessful. Peonies fall into two main categories: the herbaceous type, which dies back to the ground each winter, and the woody tree peony, which retains a permanent, shrub-like structure. Utilizing specialized root cuttings for herbaceous varieties and grafting techniques for tree peonies allows gardeners to multiply their favorite plants, ensuring the new plants are true clones of the parent.
Understanding Peony Propagation Limitations
Attempting to grow peonies from standard stem cuttings often fails due to the plant’s natural structure. Herbaceous peonies lack the internal tissue organization necessary to easily form adventitious roots from stem tissue, as their stems are primarily annual structures designed only to support foliage and flowers.
Peonies are biologically programmed to regenerate from their underground storage organs, specifically the tuberous roots and the crown, which contains the dormant buds, or “eyes.” While division is the most reliable method for increasing herbaceous stock, successful propagation methods like root cuttings and grafting bypass the limitations of stem tissue by focusing on the parts of the plant that naturally support new growth.
Step-by-Step Guide to Root Cuttings
Propagating herbaceous peonies using root cuttings is a practical and effective method that utilizes the storage roots rather than the stems. The ideal time is during the plant’s dormant season, typically in late fall after the foliage has died back or in early spring before new growth begins. This timing minimizes stress and provides the root segments with the cold period necessary for success.
Harvesting and Preparing Roots
Carefully excavate a portion of the parent plant’s root system, aiming for thick, fleshy feeder roots that are not part of the main crown. The roots should be approximately pencil-thickness or slightly larger. Ensure all tools are sterile to prevent disease. Once harvested, thoroughly clean the roots to remove all soil particles.
Cut the cleaned roots into segments roughly two to four inches long. Make a straight cut on the end closest to the crown and a slanted cut on the end farthest from the crown. This difference in cut angle helps you remember the correct polarity, crucial for proper orientation during planting. These roots contain latent meristematic tissue capable of forming new buds.
Planting the Cuttings
Plant the prepared segments horizontally or slightly angled in a propagation medium, such as a mix of sand and vermiculite, which provides excellent drainage and aeration. Plant the segments about one to two inches deep.
Ensure the end closer to the crown is positioned higher if planting at an angle. Keep the medium consistently moist but not saturated. Place the cuttings in a cool, dark location, such as a cold frame or unheated basement, for several months to encourage root and bud formation.
Specialized Grafting Techniques
Grafting is the preferred method for propagating tree peonies (P. suffruticosa). These woody shrubs do not die back to the ground and are difficult to root from cuttings. This technique involves joining a desired variety, called the scion, onto an established root system, known as the rootstock.
Tree peony grafting is typically performed in late summer or early fall (mid-August through October), when the scion buds have matured. The scion is a short section of the current season’s growth containing one or two prominent buds. This section is shaped into a wedge and fitted precisely onto a piece of herbaceous peony rootstock, often called a “nurse root.”
The herbaceous rootstock provides immediate vigor and acts as a temporary energy source. The two pieces are tightly bound together, ensuring the cambium layers—the growth tissue beneath the bark—align perfectly to facilitate fusion. This fusion, called callusing, is promoted by keeping the grafted plants in a warm, humid environment (75 to 85 degrees Fahrenheit) for several weeks until the graft has successfully healed.
Establishing Your New Peony Plant
Successfully propagated peony plants require a careful transition to their permanent location. The best time for transplanting is generally in the fall, allowing the plant to establish its root system during the dormant season. The chosen site should receive at least six hours of direct sunlight daily and have rich, well-drained soil with a neutral to slightly alkaline pH.
Planting Depth for Herbaceous Peonies
Proper planting depth influences the plant’s ability to flower. For herbaceous peonies grown from root cuttings, the newly formed crown should be positioned shallowly. The buds must be no more than one to two inches below the soil surface. Planting too deeply is the most common reason for a peony to fail to bloom, a condition often called “going blind.”
Planting Depth for Tree Peonies
For grafted tree peonies, the graft union must be buried approximately three to six inches below the soil line. This deep planting encourages the scion to develop its own root system, making it independent of the nurse root. Adequate spacing for air circulation and an initial deep watering helps the new peony establish itself.