Simply defined, grafting involves taking the stem of one plant and uniting or fusing it with the living stem or root tissues on another closely related plant. The genetic makeup of the grafted plants is not altered, allowing humans to develop exact reproductions of plants with desirable characteristics, such as a flavor or color of flower or fruit. The graft union occurs when a tightly-fitting joint is made between plants and their living vascular tissues fuse successfully.
Reasons to Graft
Grafting is employed when natural propagation of plants, like making seeds or making root divisions, is impossible, cost-prohibitive or takes too much time. Resistances to disease or other environmental conditions can also lead to grafting, as one plant benefits from the hardier, more resilient roots or stems from another plant upon which it is grafted.
What Is Grafted?
Only rigid, woody plants like trees and shrubs make good grafting candidates. Within woody plants, only botanically closely related ones have the anatomy and tissues best matched to create a good union of cell tissues. Examples include different species of grape that may be grafted onto each other, or different species of apples. Rarely on a plant outside of a basic group of plants, the genus, will grafting work well. A example of intergenetic grafting success occurs between various apples (Malus), pears (Pyrus) and quinces (Cydonia). Plants that rarely flower or set seed and have poor rates of rooting when propagated by stem cuttings, or grow very slowly may make good candidates for grafting techniques.
The portion of the woody plant that is to be propagated, whether a stem or dormant bud, is called the scion. It consists of a piece of shoot with dormant buds that will produce stems and branches. The root stock, or stock, provides the new plant's root system and/or the lower part of the stem. The cambium is a layer of cells between the wood and bark of a stem from which new bark and wood cells originate. Grafting requires that the cambium layer of both the scion and stock fuse together to ensure natural flow of water, sugars and nutrients among all cells.
Keys to Successful Grafting
Four conditions must be met for grafting to be successful. First, the scion and root stock must be compatible; that is, they are closely related and have similarly structured plant tissues. Second, the scion and root stock must be at the proper physiological stage. Both needs to be actively growing, preferably vigorously. Third, the cambium layers of the scion and stock must meet. Finally, this graft union must remain moist until the wound has healed and closed itself off from outside air, sealing the working plant tissues together. Closely related to this last concern is cleanliness of the union. It must be free from disease while the plants heal.
Grafting of just a dormant bud onto a stem or root stock is known as budding, a specific descriptor of graft union. Three types of means to make a bud graft involve different cuts. Patch budding fuses scion and stock together in a patch or small rectangular chunk of tissues. Chip budding creates a small chip wedge that fits into a similarly shaped wound on the stock. T-budding, the most commonly used budding technique according to the University of Arizona, results when a bud wedge is tucked into a T-shaped cut with flaps.
When larger stem segments are used in grafting, larger-scale graft types are employed. Among the simplest is the cleft graft, which is wedging stems into another stem core's crack. Bark grafting finds the stem wedged just under a layer of inner bark. The whip or tongue graft occurs between similar diameter stems with a notched connection. If there is no notch to stabilize the union, it's a simple splice graft. Additional types of grafts exist, all varying by cuts used or tissues exposed. These include side-veneer, bridge, saddle or the in-arch, which requires a bit more finesse or skill.