Grafting is the operation of inserting a piece of a plant into another plant with the intention that it shall grow. It differs from the making of cuttings in the fact that the severed part grows in another plant rather than in the soil.
There are two general kinds of grafting--one of which inserts a piece of branch in the stock (grafting proper), and one which inserts only a bud with little or no wood attached (budding). In both cases the success of the operation depends on the growing together of the cambium of the cion (or cutting) and that of the stock. The cambium is the new and growing tissue lying underneath the bark and on the outside of the growing wood. Therefore, the line of demarcation between the bark and the wood should coincide when the cion and stock are joined.
The plant on which the severed piece is set is called the stock. The part which is removed and set into the stock is called a cion if it is a piece of a branch, or a "bud" if it is only a single bud with a bit of tissue attached.
The greater part of grafting and budding is performed when the cion or bud is nearly or quite dormant. That is, grafting is usually done late in winter and early in spring, and budding may be performed then, or late in summer, when the buds have nearly or quite matured.
The chief object of grafting is to perpetuate a kind of plant which will not reproduce itself from seed, or of which seed is very difficult to obtain. Cions or buds are therefore taken from this plant and set into whatever kind of plant is obtainable on which they will grow. Thus, if one wants to propagate the Baldwin apple, he does not for that purpose sow seeds thereof, but takes cions or buds from a Baldwin tree and grafts them into some other apple tree. The stocks are usually obtained from seeds. In the case of the apple, young plants are raised from seeds which are secured mostly from cider factories, without reference to the variety from which they came. When the seedlings have grown to a certain age, they are budded or grafted, the grafted part making the entire top of the tree; and the top bears fruit like that of the tree from which the cions were taken.
[Illustration: Fig. 174. Budding. The "bud"; the opening to receive it; the bud tied.]
There are many ways in which the union between cion and stock is made. Budding may be first discussed. It consists in inserting a bud underneath the bark of the stock, and the commonest practice is that which is shown in the illustrations. Budding is mostly performed in July, August, and early September, when the bark is still loose or in condition to peel. Twigs are cut from the tree which it is desired to propagate, and the buds are cut off with a sharp knife, a shield-shaped bit of bark (with possibly a little wood) being left with them (Fig. 174). The bud is then shoved into a slit made in the stock, and it is held in place by tying with a soft strand. In two or three weeks the bud will have "stuck" (that is, it will have grown fast to the stock), and the strand is cut to prevent its strangling the stock. Ordinarily the bud does not grow until the following spring, at which time the entire stock or branch in which the bud is inserted is cut off an inch above the bud; and the bud thereby receives all the energy of the stock. Budding is the commonest grafting operation in nurseries. Seeds of peaches may be sown in spring, and the plants which result will be ready for budding that same August. The following spring, or a year from the planting of the seed, the stock is cut off just above the bud (which is inserted near the ground), and in the fall of that year the tree is ready for sale; that is, the top is one season old and the root is two seasons old, but in the trade it is known as a one-year-old tree. In the South, the peach stock may be budded in June or early July of the year in which the seed is planted, and the bud grows into a saleable tree the same year: this is known as June budding. In apples and pears the stock is usually two years old before it is budded, and the tree is not sold until the top has grown two or three years. Budding may be performed also in the spring, in which case the bud will grow the same season. Budding is always done on young growths, preferably on those not more than one year old.
Grafting is the insertion of a small branch (or cion), usually bearing more than one bud. If grafting is employed on small stocks, it is customary to employ the whip-graft (Fig. 175). Both stock and cion are cut across diagonally, and a split made in each, so that one fits into the other. The graft is tied securely with a string, and then, if it is above ground, it is also waxed carefully.
In larger limbs or stocks, the common method is to employ the cleft-graft (Fig. 176). This consists in cutting off the stock, splitting it, and inserting a wedge-shaped cion in one or both sides of the split, taking care that the cambium layer of the cion matches that of the stock. The exposed surfaces are then securely covered with wax.
Grafting is usually performed early in the spring, just before the buds swell. The cions should have been cut before this time, when they were perfectly dormant. Cions may be stored in sand in the cellar or in the ice-house, or they may be buried in the field. The object is to keep them fresh and dormant until they are wanted.
If it is desired to change the top of an old plum, apple, or pear tree to some other variety, it is usually accomplished by means of the cleft-graft. If the tree is very young, budding or whip-grafting may be employed. On an old top the cions should begin to bear when three to four years old. All the main limbs should be grafted. It is important to keep down the suckers or watersprouts from around the grafts, and part of the remaining top should be cut away each year until the top is entirely changed over (which will result in two to four years).
A good wax for covering the exposed parts is described in the footnote on page 145.