[FIG. 15]. STOCK.
[FIG. 16]. CION.
[FIG. 17]. FIG. 18.
Cleft Grafting.—This method is employed principally upon stocks or branches of trees too large for splicing. The stock is first cut off at the point where it is desirable to insert the cion; then split with a knife, being careful to divide it, so that the edges will be kept smooth, and not rough and ragged (Fig. 15). When the knife blade is withdrawn, the cleft may be kept open with a hard wood wedge, if the stock is too large to admit of opening it with the point of the knife when ready to insert the cion. The cion may be three or four inches long, containing two or more buds; the lower end is cut wedge-shape, as shown in Fig. 16, and slightly the thickest on the side to be set against the bark of the stock. In stocks of an inch or more in diameter, two cions, one on each side, may be inserted (Fig. 17), and if both grow one should be cut away, else the tree, in later years, will be very likely to divide or break apart at this point. In stocks of an inch or less in diameter, one cion is sufficient, the top of the stock to be cut off with an upward slope, as shown in Fig. 18. After the cions are inserted, the entire exposed surface of the wood must be covered with grafting wax or waxed paper, and usually both may be employed with benefit. All the various forms of grafting in the open air, as described in my work on the "Propagation of Plants," may be employed on the chestnut, but the two here given will probably answer just as well as others for those who may have occasion to propagate this tree.
Success in Grafting.—The question has been asked many times, and will, no doubt, be frequently repeated, "What percentage of cions should one accustomed to grafting make grow?" As there are no statistics upon which to base an answer to the question, I can only give my own personal experience, and this leads me to say that seventy-five per cent may be considered an excellent, if not a high average. In some seasons this has been exceeded by at least ten per cent, while in others it has fallen as much or more below, with no apparent reason for the difference. Ninety-five per cent of the cions may push their buds, or even make a growth of several inches, then begin to die off; consequently, the time to count your successfully grafted trees is in the autumn, and not in spring or midsummer, as it is to be feared some are in the habit of doing when making a report upon what they call success in grafting nut trees.
Growth of Cions.—Cions set in strong stocks usually make a very rapid and vigorous growth, and if left unchecked, there is danger of loss by being broken or blown off by strong winds during the summer and autumn. To prevent this as much as possible, it has been my practice to pinch off the ends of the young shoots when they are about two feet long. Lateral shoots will then push out freely, and in some seasons it may be necessary to check their growth in the same way later. On feeble stocks, or those quite small, and with the less vigorous growing varieties, no summer pinching or pruning will be required. My experimental grounds are well protected upon the north and west, not only by rising ground, but by Norway spruce and American arbor vitæ hedges twice as high as the grafted chestnut trees in the nursery rows, and yet almost every season some of the stronger-growing grafts are blown out or broken off by the wind. After the first season there is little danger of injury, probably because the union between cion and stock has become stronger.
Grafting Chestnut Sprouts.—In grafting the vigorous sprouts that always spring up from the stumps of old trees that have been recently cut down, we may reasonably expect a prodigious growth of the cion the first season, as well as in succeeding ones, and if all goes well with them we will secure large bearing trees in a very few years, but such stocks are only available where old trees are sacrificed for their timber or other purposes. Having a few such sprouts on my place, they have been utilized from time to time in testing some of the newer varieties. In one instance I allowed the cion, set on a sprout about one inch in diameter, six feet from the base, to grow unchecked throughout the season, as it was in a protected position, and in the fall the entire length of the main stem and lateral branches was sixty-five feet, and all from one bud on a cion set early in the spring. The third year this tree bore about a peck of very large nuts, to which I shall have occasion to refer again under "Injurious Insects."
Grafting Large Trees.—Grafting large chestnut trees with stems of six inches or more in diameter, and with large spreading heads, is possible, but far from being economical or practicable, especially if the trees stand out where they will get the full sweep of prevailing winds. By cutting off and grafting a few of the branches at a time for several seasons in succession, one may, in a few years, succeed in getting the entire head grafted, but there is constant danger of some of the cions being broken out if they make a vigorous growth, leaving a distorted and ill-shapen tree. Having experimented somewhat in this line with variable success, I am not inclined to recommend it, because ten trees can be raised to a bearing age on moderate-sized stocks with less labor, and the results will be more satisfactory.