J. F. Jones, Nut Specialist, Lancaster, Pennsylvania
In the selection of scions of nut trees for grafting the propagator should keep in mind the fact that the wood selected must be full of vitality and must be of solid, well matured growth, that will stand the maximum amount of exposure and hardship after being grafted, as the grafts and stocks of nut trees callous or heal very slowly in comparison to fruit trees, and the scions must be of solid, well matured growth if good results are to be obtained. These requirements usually go together however and if we select scions of solid, well matured growth, we usually get scions in which the tree has stored the maximum amount of "starch" or vitality.
How to Judge Scions
The experienced propagator of nut trees can quickly distinguish between good and poor scions for grafting, but the beginner, not knowing the ear marks of good scions, often fails to select the best scions for grafting. The common mistake made by the beginner in the selection of scions of nut trees, is in selecting the smaller growth. The smaller growth is usually more pithy and lacking in vitality and gives poor results in grafting. Poor scions are usually characterized by pithy wood and a light colored, thin bark. The buds are usually farther apart than they are on good scion wood, though this is not always true, as good scions sometimes have the buds set well apart, except near the terminals. The distinguishing marks of good scions are solid, well matured growth, and a thick, dark colored bark. The buds are also larger and usually set closer together.
When to Cut Scions
Scions must be cut while the tree is still dormant and, in the case of trees that the wounds bleed when the tree is cut, as do the English and Japan walnuts, under certain conditions, we must guard against cutting scions soon after severe freezing weather and before the tree has fully recuperated. This semi-sappy condition of the trees following low temperatures that freeze the wood, seems to be a provision of nature to restore the moisture or sap lost from evaporation, and although more noticeable in some species of trees, notably the English walnut, this condition undoubtedly exists in other species of trees to a greater or less extent and we always try to avoid cutting scions of any kind soon after hard, freezing weather. I have found scions of the English and Japan walnuts, cut from trees in this condition, to be practically worthless for propagation, although the scions may have been cut in late winter, long before the sap gets up in the tree, naturally.
Handling and Keeping Scions
Scions of nut trees for grafting should be handled carefully to avoid rubbing off the buds, although this is not so important with nut trees as with fruit trees, for the reason that the more important nut trees such as the various walnuts, pecan and hickories have compound buds and if the larger buds should be destroyed the secondary buds may be counted upon to grow. The scions should be tied in bunches of a convenient size to handle and, after being well tied and carefully labeled, should be packed in paper lined boxes that will prevent evaporation of moisture in the parking material. Any material that will absorb and hold moisture and that will not heat when bulked, will answer the purpose for packing scions, but we have found sphagnum moss to be the best material for this purpose. This material can be obtained from the local florists or dealers in cut flowers usually. Sphagnum will absorb a good deal of moisture without actually becoming wet and will also hold this moisture and give it off more slowly than any other packing material with which I am familiar. This is especially important in keeping scions of nut trees in good condition for grafting, because, if packed too damp, the scions are soon spoiled for grafting, even if kept at a low temperature.
As a precaution against fungi, we usually use bordeaux mixture, two thirds standard strength, to dampen moss for packing scions, especially if they are to remain in storage several months.
Our rule is to use moss only slightly damp to the touch and if used in sufficient quantity, say two or three times as much bulk as we have of scions, we find no trouble in keeping scions in perfect condition for months. In fact, as an experiment, we have carried pecan scions in cold storage and without re-packing for fifteen months and then get a fair stand of grafts to grow.