Grafting

Reasons for Grafting and Budding

Budding and grafting may increase the productivity of certain horticultural crops because they make it possible to do the following things:

  • Change varieties or cultivars. An older established orchard of fruiting trees may become obsolete as newer varieties or cultivars are developed. The newer varieties may offer improved insect or disease resistance, better drought tolerance, or higher yields. As long as the scion is compatible with the rootstock, the older orchard may be top worked using the improved variety or cultivar.

  • Optimize cross-pollination and pollination. Certain fruit trees are not self-pollinating; they require pollination by a second fruit tree, usually of another variety. This process is known as cross-pollination. Portions of a tree or entire trees may be pollinated with the second variety to ensure fruit set. For example, some hollies are dioecious, meaning that a given plant has either male or female flowers but not both. To ensure good fruit set on the female (pistillate) plant, a male (staminate) plant must be growing nearby. Where this is not possible, the chances that cross-pollination will occur can be increased by grafting a scion from a male plant onto the female plant.

  • Take advantage of particular rootstocks. Compared to the selected scion, certain rootstocks have superior growth habits, disease and insect resistance, and drought tolerance. For example, when used as rootstock for commercial apple varieties, the French crabapple (Malus sylvestris, Mill.) can increase resistance to crown gall and hairy root. Malling VIII and Malling IX are used as dwarfing rootstocks for apple trees when full-sized trees are not desired, such as in the home garden.

  • Benefit from interstocks. An interstock can be particularly valuable when the scion and rootstock are incompatible. In such cases, an interstock that is compatible with both rootstock and scion is used. An interstock could increase the disease resistance or cold hardiness of the scion. Plants also may be double worked to impart dwarfness or influence flowering and fruiting of a scion.

  • Perpetuate clones. Clones of numerous species of conifers cannot be economically reproduced from vegetative cuttings because the percentage of cuttings that root successfully is low. Many can be grafted, however, onto seedling rootstocks. Colorado blue spruce (Picea pungens, Engelm), Koster blue spruce (Picea pungens var. Kosteriana, Henry), and Moerheim spruce (Picea pungens var. Moerheimii, Rujis) are commonly grafted onto Norway spruce (Picea abies, Karst.) or Sitka spruce (Picea sitchensis, Carr.) rootstock to perpetuate desirable clones. Numerous clones of Japanese maple (Acer palmatum, Thunb.) that either root poorly or lack an extensive root system are grafted onto seedling Acer palmatum rootstock.
  • Produce certain plant forms. Numerous horticultural plants owe their beauty to the fact that they are grafted or budded onto a standard, especially those that have a weeping or cascading form. Examples include weeping hemlock (Tsuga canadensi.3, Carr. var. pendula, Beissn.), which is grafted onto seedling hemlock rootstock (Tsuga canadensis, Carr.); weeping flowering cherry (Prunus subhietella var. pendula, Tanaka), which is grafted onto Mazzard cherry rootstock (Prunus avium, L.); and weeping dogwood (Cornus florida, L. var. pendula, Dipp.), which is grafted onto flowering dogwood rootstock (Cornus florida, L.). In most cases, multiple scions are grafted or budded 3 feet or higher on the main stem of the rootstock. When used this way, the rootstock is referred to as a standard. It may require staking for several years until the standard is large enough to support the cascading or weeping top.

  • Repair damaged plants. Large trees or specimen plants can be damaged easily at or slightly above the soil line. The damage may be caused by maintenance equipment (such as lawnmowers, trenchers, or construction equipment), or by disease, rodents, or winter storms. The damage can often be repaired by planting several seedlings of the same species around the injured tree and grafting them above the injury. This procedure is referred to as inarching, approach grafting, or bridge grafting.

  • Increase the growth rate of seedlings. The seedling progeny of many fruit and nut breeding programs, if left to develop naturally, may require 8 to 12 years to become fruitful. However, if these progenies are grafted onto established plants, the time required for them to flower and fruit is reduced dramatically. Another way to increase the growth rate of seedlings is to graft more than one seedling onto a mature plant. Using this procedure as a breeding tool saves time, space, and money.

  • Index viruses. Many plants carry viruses, although the symptoms may not always be obvious or even visible. The presence or absence of the virus in the suspect plant can be confirmed by grafting scions from the plant onto another plant that is highly susceptible and will display prominent symptoms.