Inexperienced propagators should get it clearly in mind that union takes place only in the new growth. This new growth builds up from the cambium layer, which is the outside layer of wood cells that lies just beneath and in contact with the bark.
This is why it is so vitally necessary that the lines between the bark and cambium be placed in parallel contact as closely as possible, in the splice and cleft grafts. Never mind if the outside of the bark of scion and do not match perfectly, due to differences in the thickness of the bark. It is the inside line of the bark that must match.
Actual union takes place along this cambial line. The old wood of the wedge and cleft cannot, and never does, unite.
A word about scions. I seldom use a scion with more than two buds. The best scion wood is of the previous season's growth, if it is of good diameter and well ripened. Thin, slender twigs give poor results. On old, slow-growing, bearing trees it is sometimes not possible to get good scion wood one year old. In this case it is best to take some of the older wood in cutting the scion. When used, the wedge should be cut from the two-year wood, just below the one-year wood, with the top of the scion carrying two or three buds on the new wood. The tip of the scion should be waxed, if cut.
Scions should be cut when perfectly dormant and kept in cold storage until used. If kept too warm and wet the buds may swell, making the scions worthless.
It is quite possible to cut the scions about three weeks before the buds begin to swell and get good results by grafting immediately. The chief danger from this practice is that late frosts may nip the buds after starting, which is fatal to the new scion.
Waxing all cut surfaces, including the tip of the scion, should be practiced except as explained when the side graft is used for walnuts. Some advocate waxing the entire scion, also. If this is done I think it better to leave the buds unwaxed.
Have your knife very sharp. A broad blade is desirable in a grafting knife, as it helps in making smooth, flat surfaces in wedges and clefts. For budding, use a knife with a narrow blade, but also very sharp. Develop skill in making the scion wedge, and in cutting the cleft just the right depth and width for the scion selected. Experiment on worthless material until you get the knack. If you are a good, natural-born whittler you will find it a greater asset than a college degree.
Beginnings in Walnut Grafting
By C. C. Lounsberry, Iowa