Grafting is a method of taking a branch, or scion, from a plant and adding it to another plant to transfer desirable traits between plants. Roots from a plant can be used as a place to graft scion from a parent tree.
Rootstock from a tree can be used to transfer desirable traits to a scion from a tree that has good fruit production but lacks a healthy root system. Rootstock can be used to make a tree that is not otherwise resistant to a disease resistant, and can make trees that do not want to grow in certain conditions adapted to do so.
Some cultivars, or varieties, of trees and plants do not actually come from seeds. Some cultivars cannot be reproduced from seed and must be grafted. A Haralson apple tree, for example, can only be created from grafting, as the Haralson seed does not produce the Haralson variety.
To graft a tree, a healthy twig from a tree must be collected to attach to the rootstock. This is called a scion. A scion is cut from a new, thin branch, at the node or budding area and is usually six inches long. This scion can be kept in a refrigerator until the spring--when it would begin budding--to be grafted to a root.
Rootstock is collected from a healthy, desirable tree, that is about four inches long and larger, or the same size as the scion. The scion is attached to the rootstock using grafting tape and left in a cool place until the graft takes. The scion will usually attach in a few weeks.
Grafting is sometimes difficult. Some grafts will not take, even with cultivars that have successfully grafted with certain varieties before. Grafting properly means trial and error, testing different varieties until they take properly.