Grafting is a centuries-old horticultural technique that allows two different plants to be physically joined to grow as a single organism. This method of propagation is widely used across the agricultural industry, particularly for fruit trees and ornamental varieties difficult to reproduce by other means. By combining the strengths of two distinct plants, growers create a new tree that possesses specific, desirable traits. The resulting tree is a biological composite, with its upper and lower halves maintaining their original genetic identities.
Defining the Grafting Process
The process of grafting requires the careful union of two separate plant parts, referred to as the scion and the rootstock. The scion is the desired top portion, typically a short section of a shoot or a single bud, which grows into the tree’s canopy and produces the flowers or fruit. Conversely, the rootstock is the lower portion, providing the root system and sometimes a portion of the trunk.
For the graft to succeed, a biological bridge must form between the two tissues. This happens when the vascular cambium layers of the scion and rootstock are aligned and fuse together. The cambium is a thin layer of actively dividing cells located just beneath the bark. Its successful merger produces the new xylem and phloem tissues necessary for water and nutrient transport throughout the plant.
The Specific Reasons for Grafting
Grafting offers several distinct advantages over growing trees from seeds, especially in commercial horticulture. One primary reason is the ability to clone desirable traits, ensuring the new tree is an exact genetic replica of the parent tree that supplied the scion. This is important for many fruit cultivars that will not “come true” from seed, meaning their offspring would lack the desired fruit quality.
The rootstock also serves a practical purpose, often being selected for its inherent disease or pest resistance. Utilizing a rootstock resistant to soil-borne pathogens protects the sensitive scion from infection. Growers also use specific rootstocks to control the mature size of the tree, a practice known as dwarfing. Certain rootstocks limit the scion’s vigor, resulting in a smaller, more manageable tree that produces fruit sooner than a seedling-grown tree.
How a Grafted Tree is Created
The creation of a grafted tree is a delicate procedure that requires clean, precise cuts and optimal timing, usually in late winter or early spring when the plants are dormant. The fundamental requirement is to ensure the cambium layers of the scion and the rootstock make intimate contact. A clean, straight cut is made on the rootstock, and a complementary cut is made on the scion, allowing the two pieces to fit together like a puzzle.
One common method is the whip-and-tongue graft, which involves cutting a long, sloping slice on both pieces and then making a small, interlocking cut, or “tongue,” to hold them securely together. Another technique is T-budding, where a single bud from the scion is inserted into a T-shaped slit made in the rootstock’s bark.
Once the pieces are fitted, the entire union is tightly bound with specialized grafting tape or rubber strips to maintain pressure and exclude air. The exposed cut surfaces are then often sealed with grafting wax or paint to prevent moisture loss and protect the vulnerable tissue while the new cells form a callus bridge.
Caring for Grafted Trees
Caring for a newly grafted tree involves specific maintenance to ensure the scion flourishes and the union remains strong. The most persistent maintenance task is the identification and removal of rootstock suckers. These are shoots that sprout from the rootstock below the graft union, and they possess the original, often less-desirable genetics of the rootstock.
If left to grow, these suckers will aggressively draw water and nutrients, outcompeting the grafted scion and potentially weakening or killing the desired variety. Suckers growing from the ground or trunk must be pruned or torn off immediately and as close to their point of origin as possible. Additionally, the graft site should be protected from physical damage from yard equipment and kept free of mulch to prevent moisture from compromising the union.