INTRO TO GRAFTING
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, called the scion, of one plant grows on the root system, called the 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.
Many types of grafting exist, however not all forms of grafting are appropriate for all kinds of trees. Fruit trees are primarily grafted using the types of grafting we will discuss below.
TYPES OF GRAFTING
WHIP AND TONGUE GRAFTING
The whip and tongue technique is most commonly used to graft nursery crops or woody ornamentals. Both the rootstock and scion should be of equal size and preferably no more than 1⁄2-inch in diameter. The technique is similar to splice grafting except that the whip on the rootstock holds the tongue of the scion in place (and vice versa). This leaves both hands free to wrap the joint.
For the whip and tongue graft, make similar cuts on both the stock and scion. These cuts should be made with a single draw of the knife and should have a smooth surface so that the two can develop a good graft union. Up to this point, rootstock and scion are cut the same as for a splice graft.
PREPARING THE STOCK AND SCION
Cut off the stock using a diagonal cut. The cut should be four to five times longer than the diameter of the stock to be grafted. Make the same kind of cut at the base of the scion. Next, place the blade of the knife across the cut end of the stock, halfway between the bark and pith (on the upper part of the cut surface). Use a single knife stroke to draw the blade down at an angle through the wood and pith. Stop at the base of the initial diagonal cut.This second cut must not follow the grain of the wood but should run parallel to the first cut.
INSERTING THE SCION
Prepare the scion in the same way. Fit the scion into the rootstock so that they interlock whip and tongue. Be certain that the cambium layers are aligned.
SECURING THE GRAFT
Wrap the junction completely with a grafting strip or twine, covering the entire graft union. Never allow the binding material to girdle the stem.
T-budding is most commonly used for summer budding of apples, crabapples, dogwoods, peaches, and pears. T-budding must be done when the bark will "slip." Slipping means that, when cut, the bark easily lifts or peels in one uniform layer from the underlying wood without tearing. The exact time when this condition occurs depends on soil moisture, temperature, and time of year. It varies with species and variety. Dry or excessively hot or cold weather can shorten the period when bark slips. Irrigation can be valuable in extending the T-budding season.
Since budding is usually done during the warm summer months, two other precautions are commonly taken to ensure success. First, buds should not be added when the air temperature exceeds 90°F. Second, buds should be inserted on the cooler north or east sides of stems.
PREPARING THE STOCK
Budding knives usually have a curved tip, making it easier to cut a T-shaped slit. First, insert the point of the knife and use asinglemotion to cut the top of the T. Then without removing the point of the knife, twist it perpendicularly to the original cut and rock the blade horizontally down the stem to make the vertical slit of the T. If bark is slipping properly, a slight twist of the knife at the end of this cut will pop open the flaps of the cut and make it easier to insert the bud. In practice, the top of the T is usually slanted slightly.
This same type of cut can be made using two separate strokes, one vertical and one horizontal, and then using the back of the budding knife tip to pry up the flaps slightly. Although much slower, this technique may be easier.
REMOVING BUDS FROM THE BUDSTICK
The bud to be inserted is often just a shield of bark with a bud attached or a very thin layer of wood with both the bark shield and bud attached. Various techniques can be used to make these cuts, but the shape of the cut remains the same.
Begin the first scion cut about 1⁄2-inch below the bud and draw the knife upward just under the bark to a point at least 1⁄4-inch above the bud. Grasp the petiole from the detached leaf between the thumb and forefinger of the free hand. Make the second cut by rotating the knife blade straight across the horizontal axis of the budstick and about 1⁄4 inch above the desired bud. This cut should be deep enough to remove the bud, its shield of bark, and a thin sliver of wood.
The cut surface of the rootstock and bud must stay clean. Do not touch these parts with your fingers. Do not set buds down or put them in your mouth. Contaminated bud scions will fail.
INSERTING THE BUD
Insert the bud shield into the T flaps of the stock and slide it down to ensure that it makes intimate contact with the rootstock.
SECURING THE BUD
Pull the cut together by winding a 4- or 5-inch long budding rubber around the stem to hold the flaps tightly over the bud shield and prevent drying. Secure the budding rubber by overlapping all windings and tucking the end under the last turn. Do not cover the bud.
Chip budding is a technique that may be used whenever mature buds are available. Because the bark does not have to "slip," the chip-budding season is longer than the T-budding season. Species whose bark does not slip easily without tearing may be propagated more successfully by chip budding than by T-budding.
PREPARING THE STOCK AND THE SCION BUD
Although all the basics in handling budwood and stock are the same for chip budding and T-budding, the cuts made in chip budding differ radically. The first cut on both stock and scion is made at a 45 to 60° downward angle to a depth of about 1⁄8-inch. After making this cut on a smooth part of the rootstock, start the second cut about 3⁄4-inch higher and draw the knife down to meet the first cut. (The exact spacing between the cuts varies with species and the size of the buds.) Then remove the chip.
Cuts on both the scion (to remove the bud) and the rootstock (to insert the bud) should be exactly the same. Although the exact location is not essential, the bud is usually positioned one-third of the way down from the beginning of the cut. If the bud shield is significantly narrower than the rootstock cut, line up one side exactly.
SECURING THE BUD
Wrapping is extremely important in chip budding. If all exposed edges of the cut are not covered, the bud will dry out before it can take. Chip budding has become more popular over the past 5 years because of the availability of thin (2-mil) polyethylene tape as a wrapping material. This tape is wrapped to overlap all of the injury, including the bud, and forms a miniature plastic greenhouse over the healing graft.