Avocado grafting is a horticultural technique used to join a desirable avocado variety, known as the scion, onto a different root system, called the rootstock. This process is utilized primarily because avocado trees grown from seed often take up to a decade to bear fruit, and the resulting fruit quality is unpredictable due to genetic variation. By grafting, growers can propagate a specific, high-quality cultivar onto a hardy rootstock, ensuring the new tree produces the desired fruit much faster, often within a few years. The technique combines the robust root system of one tree with the fruit-producing branch of another, giving the new plant the best traits of both.
Essential Preparation and Timing
Success in avocado grafting depends heavily on proper preparation and precise timing. The ideal time for grafting is in late winter through early spring. This period allows the graft a long growing season and utilizes the plant’s winter-stored sugars for vigorous spring growth. Grafting is most successful when the tree’s cambium layer is actively growing.
A few specialized tools are necessary for making the clean, precise cuts required for a successful union. A sharp knife, such as a grafting knife or scalpel, is required to make smooth cuts that maximize cambium contact. Before use, all cutting instruments must be sterilized with rubbing alcohol to prevent the introduction of pathogens. Grafting tape or budding rubber is needed to secure the scion to the rootstock, and grafting wax or sealant is used to cover all exposed cuts to prevent desiccation.
Material selection involves choosing both a healthy rootstock and a suitable scion. The rootstock is the lower part of the plant, which provides the root system. It should have a diameter similar to the scion, ideally between 1/4 and 1/2 inch. The scion wood, which will become the fruiting part of the tree, must be collected from a known, high-producing, disease-free tree.
The scion should be collected while the wood is mature but dormant, often pencil-thickness, and approximately four to six inches long, containing three to four healthy buds. To prevent the scion from drying out, it should be kept cool and moist until immediately before grafting.
Step-by-Step Grafting Techniques
The physical act of grafting involves quickly and cleanly joining the rootstock and scion to ensure their cambium layers align and fuse. Speed is important to prevent the delicate cut surfaces from drying out. The two most reliable methods for grafting avocados are the Cleft Graft and the Whip-and-Tongue Graft, each suited for different rootstock sizes.
Cleft Graft
The Cleft Graft is often used for rootstocks up to half an inch in diameter. This method involves preparing the scion into a wedge shape by making two long, sloping cuts on opposite sides of the base. The rootstock is cut horizontally to remove the top, and a vertical slit, or cleft, is made down the center of the cut surface. The scion wedge is inserted carefully into this cleft, ensuring that at least one side of the scion’s cambium layer aligns with the rootstock’s cambium.
Whip-and-Tongue Graft
The Whip-and-Tongue Graft is used for smaller-diameter rootstocks and scions of matching size, typically between 1/4 and 1/2 inch. Both the rootstock and the scion are first given a long, slanting cut of about one to two inches in length. A downward slicing cut, or “tongue,” is then made into the wood of both sloping surfaces. The scion and rootstock are then interlocked by fitting the tongues together, which creates a secure physical bond.
After either method, the entire graft union must be wrapped tightly with grafting tape or budding rubber to hold the scion and rootstock firmly in place. All exposed cut surfaces, including the tip of the scion, must be sealed with grafting wax, Parafilm, or tree seal. This sealing prevents moisture loss from the scion and protects the wound from pathogens and pests.
Post-Graft Care and Monitoring for Success
Immediate care following the grafting process is essential for ensuring a successful union. The newly grafted tree must be protected from direct, intense sunlight, as the exposed scion and rootstock are highly susceptible to sunburn and desiccation. Placing the grafted plant in a shaded area or using a protective paper bag over the graft union until new leaves emerge provides the necessary protection.
Monitoring the graft closely over the next several weeks will reveal whether the union is taking hold. A successful graft will show signs of life as the buds on the scion begin to swell and push out new growth. Conversely, a failed graft will appear dark, shriveled, or dry, indicating that the vascular tissues have not successfully connected. The initial healing process, where the cambium layers form a callus, can take between three to six weeks.
The wrapping material should remain in place to support the union until the scion has begun to grow and the union appears fully healed, typically after a few months. Once the union is strong, the tape must be carefully removed to prevent the expanding trunk from being girdled. Any new shoots that emerge from the rootstock below the graft union, known as suckers, must be promptly removed, as they divert energy away from the desired scion.