A rootstock is one method of propagating, or starting, plants. Rootstocks are commonly used when planting trees, but they are a viable method of propagating any plant that does not easily start from seed. Tree rootstocks are plants or stumps with healthy, established root systems.
One of the trees most commonly grown from rootstocks is the apple tree. This is because many apple trees are susceptible to disease, making rootstock propagation one of the most viable methods for hobby gardeners and orchard growers alike. Apple tree rootstock has been used since the early 1900s with little change.
Aside from creating a hardier plant, using fruit tree rootstock ensures that growers know exactly how tall their plant will be. Labels are marked with a number, indicating the size of the mature plant. A label marked with the number one is 10 to 20 percent of a full-size tree, while a number two indicates a tree 20 to 30 percent of a full-size tree. The numbering system for rootstocks concludes at the number 10, which is a full-sized tree.
There are two basic methods of grafting onto rootstocks. In the first method, the scion, or a bud and piece of bark from the tree, are bound together. The buds and rootstocks grow together into a completely new tree. This method of growth is called budding or bud grafting.
The second most common method involves placing the rootstock onto an established branch, before binding the two together. This method of grafting is known as “whip and tongue grafting.” It is used when there is a viable portion of the tree still available for growth.
Budding or grafting has several additional benefits. Growers can create trees for all soil, water and light requirements. On a small hobbyist scale, the number of trees needed to create an ideal hybrid is prohibitive, but commercial growers have the means necessary to accomplish this. Trees grafted from rootstocks are less susceptible to certain kinds of bacteria, fungi and pests, depending upon the strengths and weaknesses of the individual rootstock and scion.
It is also possible for gardeners to use rootstocks to replenish plants that have been damaged by fire, lightening or drought. If the roots of the plant are still alive and healthy, a similar plant or live piece of the same plant can be grafted onto the plant's or tree's own root system. This process is called “own root” grafting.