By: Jonathan Sturm
Grafting means joining part of a plant onto another. Usually, this is done to propagate plants that do not come true to type from seed and cannot be struck from cuttings. Another reason for grafting is that different kinds of rootstocks can impart desired characteristics to the plant. Examples of this include resistance to root disease, increased vigour, decreased vigour (dwarfing) and resistance to pests. Fruit trees needing cross-pollination are often grafted with two, or three, suitable varieties for the home gardener who cannot spare the space for two or three trees. Budding is the term used when the plant part being applied to the rootstock is a bud rather than a shoot.
|Bud||a scion with one bud|
|Bud Stick||shoot of current year's growth used to supply buds|
|Callous||scar tissue formed by plant to heal a wound|
|Rework||to bud or graft onto a mature plant that was previously budded or grafted to another variety when young.|
|Scion||the bud or shoot to be attached to the root stock.|
|Scion wood||a dormant shoot that grew last year, though occasionally older wood is used.|
|Stock (also, root stock)||This is the part that has, or will have, roots.|
|Work||to bud or graft a young plant.|
The ancient Greeks practised grafting. Budding is of more recent origin. In both cases the principle is the same. Just under the bark of a plant is a layer of actively growing tissue, called the cambium. This layer must be mated between the scion and the stock. A callous then forms around the union, creating a permanent joint.
For this to work, the two plant materials must be compatible. For example, some pear varieties can be grafted onto quince rootstock with great benefit. Most varieties cannot. No pear variety can be grafted onto apple or stone fruit root stocks. In the instance of the incompatibility between some pear varieties and the quince root stock, the incompatible varieties can be grafted onto a compatible pear variety that has been grafted onto the quince root stock.
Whip and Tongue Graft
This is the most popular grafting method. It can be performed when the scion and stock are dormant, or just as the stock begins to move in the spring. Using a very sharp knife, make a long, sloping cut on the scion and a matching one on the stock. The cut should be perfectly straight. Make a split one third of the way along each cut and push the scion onto the stock, as illustrated. The union must then be sealed against moisture loss. Special plastic grafting tape is readily available, but discarded bicycle inner tube works just as well. In bygone days, raffia (a type of grass) was used and melted wax applied after it was in place. The plastic tape must be removed when the graft has well taken, to avoid strangulation.
This is used to rework established trees. An inverted L is cut through the bark of the tree, often a limb. The scion is cut as for a whip and tongue, but the split for the tongue is not made. Instead, a slice is taken off one side. Insert the scion under the flap so that the slice is against the bark of the vertical part of the cut. Put a tack through the scion to secure it and paint the union with grafting mastic. Traditionally, melted wax was used for this.
This technique is used to rework trees that have been cut back. A vertical slit is made in the bark and a scion prepared as for inverted L grafting is inserted into the slit. The scion is tacked into place and the join covered with grafting mastic. Several scions are often grafted onto the stock. This speeds the callousing and allows for some scions not taking.
Shield, or T Budding
This can only be done when the bark of the stock will readily lift. This is usually in mid to late summer. A bud stick is cut from a vigorous shoot of the current season's growth. If it is not to be used immediately, it can be enclosed in plastic and kept in the fridge for a few days. Remove the leaves, but not the leaf stalks. These are used as handles to manipulate the buds. Take each bud as you need it by making a long sloping cut from about 12 mm below the bud. Remove the bud by cutting it off about 18 mm above the bud. This is often then placed in the operator's mouth to prevent drying out, but it is not really necessary. The T cut is now made in the stock, just big enough to receive the bud. The flaps are pulled back and the bud inserted right way up. The leaf stalk is used to hold the bud during this part of the operation. The excess bark on the bud is cut off flush with the top of the T and the union is bound with grafting tape. The tape is removed six to eight weeks later.
The bud generally remains dormant until the following spring. As bud unions can be quite weak, the new shoot is often tied to the stub until the union is strong. The stub is then removed.
This is done where the bark will not lift readily and generally in summer to mid autumn. Cut the bud as illustrated and make a matching slot in the stock. Insert the chip so that the cambium layers touch on at least one side and bind with grafting tape. The tape can be removed six to eight weeks later.
Budding fairly high on the stem will induce more laterals in the following season of growth. Budding low on the stem will tend to produce a shoot with few or no laterals, called a whip.
For all types of grafting to succeed, the stock must not be stressed while the graft is taking. In the case of budding, this often means irrigation is necessary. Birds are often responsible for grafts not taking, as they prefer to perch on the sticks rather than established laterals.