Grafting and Budding Nursery Crop Plants
Introduction
Grafting and budding are horticultural techniques used to join parts
from two or more plants so that they appear to grow as a single
plant. In grafting, the upper part (scion) of one plant grows on the
root system (rootstock) of another plant. In the budding process, a
bud is taken from one plant and grown on another.
Although budding is considered a modern art and science, grafting is
not new. The practice of grafting can be traced back 4,000 years to
ancient China and Mesopotamia. As early as 2,000 years ago, people
recognized the incompatibility problems that may occur when grafting
olives and other fruiting trees.
Since grafting and budding are asexual or vegetative methods of
propagation, the new plant that grows from the scion or bud will be
exactly like the plant it came from. These methods of plant
reproduction are usually chosen because cuttings from the desired
plant root poorly (or not at all). Also, these methods give the plant
a certain characteristic of the rootstock - for example, hardiness,
drought tolerance, or disease resistance. Since both methods require
extensive knowledge of nursery crop species and their compatibility,
grafting and budding are two techniques that are usually practiced
only by more experienced nursery operators.
Most woody nursery plants can be grafted or budded, but both
processes are labor intensive and require a great deal of skill. For
these reasons they can be expensive and come with no guarantee of
success. The nurseryman must therefore see in them a marked advantage
over more convenient propagation techniques to justify the time and
cost.
Clones or varieties within a species can usually be grafted or budded
interchangeably. For example, Pink Sachet dogwood can be budded or
grafted onto White Flowering dogwood rootstock and vice versa.
Bradford pear can be grafted or budded onto Callery pear rootstock
and vice versa. However, Pink Sachet dogwood cannot be grafted or
budded onto Callery pear.
Grafting and budding can be performed only at very specific times
when weather conditions and the physiological stage of plant growth
are both optimum. The timing depends on the species and the technique
used. For example, conditions are usually satisfactory in June for
budding peaches, but August and early September are the best months
to bud dogwoods. Conversely, flowering pears can be grafted
while they are dormant (in December and January) or budded
during July and August.
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 lawn
mowers, 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 progeny 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.
