Grafting creates asexual plant propagation through the joining of two plants into one. Horticulturists collect a part of the desired tree, called the scion, and then use a grafting technique to grow it on a rootstock. In order for a successful grafting to take place, the scion and rootstock must be compatible and at the proper growth stage. If the grafting is performed correctly and the union is kept moist until it heals, the resulting tree will exhibit properties of both the scion and the rootstock.
According to the University of Vermont, the Chinese first documented the grafting of plants in 5000 B.C. when Feng Li began grafting almonds, peaches, pears, apples and persimmons for commercial purposes. Both Aristotle and Theophrastus mention plant grafting in their writings. Grafting was popular throughout England in the 18th century, used routinely on both apple and pear trees. Thomas Jefferson writes in 1767 in Monticello's garden journal of working with grafting cherry trees. The evolution of plant grafting has continued, being a common practice in both fruit and ornamental tree production.
Plant grafting fulfills many purposes in the cultivation of trees. Many plants are not easily propagated through cuttings, such as Norway maple and green ash. Grafting makes a clone from the plant. This provides an economic benefit, as it is usually cheaper to graft such plants than it is to grown them slowly from cuttings. Grafting also takes advantage of rootstocks that grow in poor growing conditions, are disease and pest tolerant, and feature more hardiness than the grafted scion. This allows for plants to be grown in a wider array of environments with higher success rates.
Landscapes benefit from the aesthetic benefits of grafting. Horticulturists obtain specific growth forms on ornamentals through the process of grafting. Grafting also allows for the repair of damaged plants through bridge grafting and inarching.
Fruit producers employ grafting. Seeded fruit trees may take up to 7 years to reach a flowering stage, according to Cornell University. Grafting allows for the replacement of a variety on an established tree with that of a new variety through the process of topworking. Grafting also provides for early maturity and increased growth rates.
Apple, cherry and other fruit trees can be made self-incompatible with the grafting of a pollinizer branch. Other fruit trees can enjoy several different fruits growing on one tree. For example, a citrus tree may be grafted in order to produce oranges, lemons and grapefruits all from the same tree.
Horticulturists most commonly use cleft grafting in order to change the cultivar or top growth of a tree. Performed in the early spring, the scion wood is collected and then inserted into a split in the rootstock as a wedge.
Bark grafting is used on large limbs, usually in the reworking or repairing of existing trees. After cutting a limb off, the bark is split and partially removed for the insertion of the scion.
Pairing one bud and a small piece of bark to a rootstock allows horticulturists to perform grafting through budding. Budding generally results in faster growth and a stronger union.
The graft must be properly maintained in order for successful grafting. For the first 2 years, monitoring of the graft insures that no girdling occurs. Grafting wax may need reapplication to the graft to cover any exposed areas of wood. The removal of limbs of the original variety over time will allow the tree to focus energy to the new variety.