People in China were familiar with grafting techniques as early as 1000 BC. The Romans, who were knowledgeable in the art of grafting, easily understood St. Paul when he wrote to the new Christian converts in Rome: “...and those, being a wild olive tree, were grafted in among them, and with them partakest of the root and fatness of the olive tree.” His metaphor explains concisely the purpose of grafting: to allow a secondary branch full use of the rootstock.
Horticulturists recognize grafting to serve five purposes. It becomes possible to:
- propagate plants that cannot be conveniently or economically reproduced by other means: hybrid fruits do not breed true if planted from seeds; they revert to ancestral forms.
- combine certain traits of the rootstock (disease resistance, superior root systems) with certain traits of the scion (luxuriant bloom, production of good fruit).
- alter the appearance or behavior of a plant; for example: to control the size of the tree producing a dwarf variety.
- repair damage to an existing plant and put new life into the rootstock.
- produce plant forms that could not otherwise exist; for example: to grow two or more varieties of fruit on one tree from one rootstock.
The techniques of grafting, as it was practiced in 1900, had changed little from the methods used in sixteenth-century England. Indeed, grafting is done today essentially as it was done millennia ago. Two growths, one the rootstock and the other the scion (the growth to be grafted) are cut, then bound together to heal and produce new growth.
The rootstock is the host plant. After the graft, it is rooted in soil and will provide nourishment for the entire plant. The scion is a pencil-thin one-year-old shoot several inches long, having two or more buds. Although the rootstock provides nutrients and may contribute to the hardiness of the scion, the genes of the two plants do not mingle. The scion will bear fruit true to its origins.
Two pieces of young wood of similar size produce the best graft. To be successful each growth must be cut cleanly and evenly, producing smooth, flat surfaces. The thin layer of cells growing just under the bark of the tree, called cambium, are essential in promoting a successful graft. The cambium layer of one twig is matched to the cambium layer of the second. The wound is bound with wax or tape and allowed to heal. The growth of new cambium cells at the graft forms a layer of cells called a callus, joining scion to rootstock and forming a new water- and nutrient-conduction system.
Modern techniques of grafting have changed little from a hundred years ago, although the practice today is to utilize each rootstock in its entirety, making a single graft on the rootstock stem several inches above the soil level. This procedure is known as whole-root grafting. Before the twentieth century, both whole roots and pieces of roots were used for grafting. In piece-root grafting, the apple rootstock is dug up and the larger roots are cut into three or four inch pieces (pencil diameter roots of mature trees can also be dug up and cut into pieces). Grafts are then made on the upper end of each root piece, and the newly grafted tree is planted so that the graft is several inches below soil level.
Between 1880 and 1910, a debate arose among nurserymen and orchardists as to which was the best grafting procedure: whole-root or piece-root. Both had their proponents but by 1920, piece-root grafting had been largely abandoned.
Espalier (i SPALL yer) is used by orchardists to train and control the growth and shape of trees. With a fence, wall, or wire trellis to provide support, the tree is pruned and the branches tied to create a two-
dimensional plant growing flat against the support. From the French spalla (“shoulder”), the word "espalier" refers to the structure the trees lean on. Espalier is sometimes referred to as “trellised trees.” The technique originated in medieval Europe as a practical response to growing fruit in a limited space and was popular in English walled gardens of the 1700’s, both in England and in the American colonies.
The trellised trees are carefully tended and shaped in order to provide a maximum amount of sunshine to every branch, thereby producing more fruit earlier. Dwarf varieties of apple trees are especially suited to espalier. One- to two-year-old apple trees, pliable and easily trained, are planted in an evenly-spaced row against the wire trellis. The trellis consists of horizontal wires twelve to sixteen inches apart, the lowest being sixteen to twenty inches from the ground. The tree is secured to the wires with short lengths of string, then pruned and trained for several years until the desired shape is achieved.