Tree grafting is a horticultural technique involving the joining of two plant parts—a scion and a rootstock—to grow as a single organism. This method is used for cherry trees to reliably propagate a specific cultivar that might not grow true from seed. Grafting can also be used to repair damaged trees or to change the fruit variety of an established tree, known as top-working. Success relies on the precise alignment and subsequent healing of the vascular tissues between the two components.
Timing and Selection of Scion and Rootstock
The success of a cherry graft relies heavily on the preparation of the plant materials. Grafting is most successful during the late winter or early spring, specifically when the rootstock is fully dormant but just before its buds begin to swell. This timing ensures the rootstock has sufficient energy reserves to support the newly attached scion once active growth begins. The dormant state of the rootstock must closely match the scion material for optimal healing.
The scion, which determines the cherry variety, must be collected from healthy, one-year-old wood, ideally with a diameter similar to a pencil. This wood is identifiable by its smooth bark and the presence of plump vegetative buds; wood that has already produced flowers should be avoided. Once collected, the scion wood must be immediately labeled and stored in a cool, moist environment, typically refrigerated at 34 to 40 degrees Fahrenheit (1 to 4 degrees Celsius). Proper storage prevents the cambium layer from drying out before it can be united with the rootstock.
The rootstock serves as the foundation, providing the root system and influencing the tree’s size and adaptability. For sweet cherries, common choices include the vigorous Mazzard or the semi-dwarfing Gisela series, which offers earlier fruiting and smaller tree size. Compatibility between the Prunus species is paramount; an incompatible pairing will lead to a failure of the vascular systems to connect. Choosing a rootstock with a clean, disease-free trunk section is necessary for the grafting location.
Common Grafting Methods for Cherry Trees
Cherry grafting involves using specialized techniques to ensure maximum alignment of the cambium layers—the thin tissue responsible for cell division and healing. The specific method chosen depends on the relative diameter of the scion and the rootstock. Using sharp, sterilized grafting knives is necessary, as clean cuts facilitate rapid healing and successful vascular connection.
Whip-and-Tongue Grafting
The Whip-and-Tongue method is effective when the scion and the rootstock are nearly identical in diameter, typically between a quarter and a half-inch. Both pieces are first cut with a long, sloping cut approximately one to two inches in length, creating a large surface area for contact. Next, a second, downward-sloping cut is made into the face of the first cut, forming the “tongue” on both the scion and the rootstock. This tongue should be parallel to the stem’s axis and should not extend more than halfway down the initial sloping cut.
The scion and rootstock are then interlocked by sliding the tongues together, creating a strong, mechanical bond. This joint maximizes the contact between the cambium layers. Correct alignment is achieved when the bark of the scion matches the bark of the rootstock along at least one side of the union. Immediately after joining, the entire wound area must be tightly wrapped with grafting tape or rubber bands to hold the pieces firmly under pressure.
Cleft Grafting
Cleft grafting is the preferred technique when the rootstock is significantly larger than the scion, often used for top-working a mature cherry tree. The rootstock branch or trunk is cut cleanly across, and a sharp tool is used to split the center of the stump, creating a vertical cleft approximately two to three inches deep. This split must be uniform and clean to properly hold the scion pieces.
The scion wood is prepared by cutting its base into a long, wedge shape, ensuring the outer edge is slightly thicker than the inner edge. Two scions are then inserted into the cleft, one on each side, with the thicker edge facing outward toward the rootstock bark. The goal is to align the narrow cambium layer of the scion precisely with the cambium layer of the rootstock.
The pressure of the rootstock holding the scions is often sufficient, but the entire area must be immediately sealed with grafting wax or compound. Using two scions increases the chance of success, though only one is typically allowed to grow to maturity once the union is confirmed. Sealing prevents moisture loss from the exposed tissues and protects the union from pathogens.
Post-Graft Care and Monitoring
Immediate attention to the newly created graft union is important. Once the scion and rootstock are firmly joined and wrapped, the entire exposed surface, including the scion tip and any open cuts, must be covered. A layer of grafting wax or compound seals the wound completely, preventing the scion from desiccating and protecting the tissues from infection.
To protect the union from environmental stress, some growers apply a light-colored material, such as white paint or aluminum foil, over the graft area. This covering reflects direct sunlight, preventing the bark from overheating and minimizing temperature fluctuations that can hinder healing. Maintaining moderate soil moisture around the rootstock is also beneficial, supporting the initial flow of sap.
Monitoring for signs of a successful “take” usually begins several weeks after the operation as the growing season commences. The first positive indicator is the swelling of the vegetative buds on the scion wood, followed by the emergence of small, green leaves. If the scion begins to dry out and shrivel without bud activity, the graft has likely failed due to poor cambium alignment or desiccation.
Patience is necessary, as the vascular connection, known as the callus bridge, takes time to mature and strengthen. Once the scion shows vigorous growth, typically after the first full growing season, the binding materials can be carefully removed to prevent girdling of the expanding trunk. Any shoots that emerge from the rootstock below the graft union, known as suckers, must be pruned away immediately, as they compete with the scion and will grow the undesirable rootstock variety.