Tree grafting is an ancient horticultural practice that joins two different plant parts so they grow together as a single organism. This specialized technique allows growers to combine the desirable characteristics of one plant with the robust root system of another. It is a precise method of vegetative propagation used to control the varieties of fruit on a single tree and manage the overall size of the mature plant.
Understanding the Purpose of Grafting
Grafting offers the ability to propagate specific cultivars that would not grow true from seed. For example, the seed from a desired apple variety will not produce a tree with the exact same fruit characteristics, making grafting the only way to retain that specific genetic identity. The process is also commonly used to change the variety of fruit on an already mature tree, a technique known as topworking.
This method allows a gardener to cultivate multiple different fruit types on a single root system, such as grafting several varieties of plums onto one tree. Grafting is also used for controlling tree size by selecting a dwarfing or semi-dwarfing rootstock. The rootstock, which is the lower portion of the graft, provides the root system and can confer greater resilience, offering resistance to soil-borne diseases or better adaptation to poor soil conditions.
Essential Tools and Optimal Timing
Successful grafting requires careful preparation of both the plant materials and the tools. The two components involved are the scion, the small piece of the desired variety, and the rootstock, the established plant or branch that provides the root system. Scion wood should be collected from the previous season’s growth while the tree is fully dormant, typically in late winter, and stored carefully to prevent drying out.
The best time to perform the actual graft is generally in late winter or early spring, just before the rootstock begins to break dormancy and the sap starts to flow. This timing ensures the dormant scion is joined to a rootstock that is actively beginning its growing cycle. Clean, precise cuts are necessary, requiring a specialized grafting knife that is razor-sharp and sterilized to prevent the transmission of plant diseases.
Sharp pruning shears are needed to cut the scion wood and prepare the rootstock branch for the graft. Once the union is made, materials like grafting tape, Parafilm, or grafting wax are used to secure the connection and seal the exposed tissue. The sealing compound prevents desiccation, the primary cause of graft failure, and protects the wound from pathogens and pests.
Step-by-Step Guide to Common Grafting Methods
The Whip-and-Tongue graft is one of the most reliable methods for joining scion and rootstock of similar diameter, typically pencil-thickness. This technique creates a strong mechanical lock and maximizes contact between the cambium layers of the two plant parts. The cambium is a thin layer of actively dividing cells located just beneath the bark, and its alignment is the most important factor for a successful union.
The process begins by making a long, smooth, slanting cut, approximately two to three inches long, at the base of the scion and the top of the rootstock. These cuts must be identical to ensure a perfect fit and expose a large surface area of the cambium. A second cut, known as the “tongue,” is then made into the center of the first cut, going about halfway down its length on both the scion and the rootstock.
The scion and rootstock are then interlocked by their respective tongues, pushing them together firmly until the cut surfaces match closely. If the diameters are slightly different, the cambium layers only need to align on one side, but a tighter fit increases the chance of success. Immediately after joining, the entire union is wrapped tightly with grafting tape or Parafilm to maintain pressure and exclude air and moisture, which is essential for the vascular tissues to knit together.
Caring for the Newly Grafted Union
After the graft is bound and sealed, the focus shifts to monitoring the union and encouraging the scion’s growth. The seal must be maintained and checked regularly, as cracks in the wax or tape can allow the scion wood to dry out, leading to failure. The new graft should also be protected from strong winds and excessive direct sunlight in the initial weeks to minimize stress.
A successful “take” is indicated by the scion’s buds swelling and beginning to push out new leaves and shoots, which may occur within a few weeks to a couple of months. During this time, any new growth, known as suckers, that appears on the rootstock below the graft union must be immediately rubbed off or pruned away. This ensures the rootstock’s energy is directed solely toward healing the graft and supporting the desired scion growth.
The binding material must be removed before it begins to girdle the expanding branch, which usually happens by mid-summer or in the fall of the first growing season. If non-biodegradable tape was used, a careful cut can be made along the tape’s length to relieve pressure without disturbing the newly formed vascular connection. Allowing the graft to heal completely and avoiding the development of fruit in the first year supports a stronger, long-term union.