The Importance of Stock and Scion Relationship in Hickory and Walnut
CARL WESCHCKE, St. Paul, Minnesota
Twenty-five years of practical study and living with the hickories ought to suffice to make a success in growing these trees for their delicious product. However, it is only in the twenty-eighth year of such work that I have made an important discovery about the particular hickory with which I have had the most success; I refer to the variety known as the Weschcke shagbark hickory.
I began to graft such varieties as Beaver and Fairbanks (bitternut—shagbark hybrid) hickory on Wisconsin native bitternut hickory (Carya cordiformis) in 1920, and some grafts are doing very well at this time, 1948, but they are practically barren of fruit. Since then I have accumulated more varieties to test from many different sources, to continue the work down to the present day. During that time I noticed, but did not appreciate, the significance of the relationship of growth between scion and root system. True, I have been very cognizant of the so-called compatibility between stock and scion in the hickory family, and have written about this matter for publication several times, but I was then more concerned with the stock and scion living together in a harmonious state of existence and health without realizing that there was something else necessary to this relationship in order to promote heavy bearing.
+Experiments in Grafting Black Walnuts+
Parallel to these early experiments, I was grafting in the same family as the hickories, known as the walnut, or Juglandaceae family, using wild native butternut (Juglans cinerea) as a stock for grafting to such varieties as the Thomas, Ohio, Stabler and Ten Eyck black walnut (J. nigra). Some of these trees, so grafted, exist today, being more than 25 years old, and they have never borne more than a hatful of walnuts to a tree, even when they became large trees. Most of them are entirely barren year after year. I often remarked to persons who were interested in this phase of my work, that the black walnut was non-productive on the butternut root system, but it was very evident that there was not completecompatibility because the walnut scion greatly outgrew the butternut stock causing a marked difference in their trunk diameters just below and above the union. This great difference, the butternut being so much smaller, was no doubt the cause of a shortage of food supply elaborated through the bark circumference which limited the top to a mere growth of leaves, not leaving sufficient additional supply for the growth of fruit.
My observation among the hickories, with which I did far more experimental work than with the walnuts, was beclouded by the fact that many successful, apparently compatible varieties, grew and throve on the native bitternut stock without bearing fruit, except for just a few nuts occasionally; and yet there was no apparent difference between the scion diameter and the trunk diameter, nothing like the overgrowth of the black walnut when grafted on butternut. So it took many years and a different growth phenomenon to open my eyes as to what was the trouble in getting hickories to bear on foreign root systems.
The final solution of the problem was determined by my observation this year of grafted hickories of several sizes and ages were Weschcke shagbark (C. ovata)[33] scions and other hickory scions, such as Siers, Bridgewater, Deveaux, Beaver, and Fairbanks have been grafted on the same tree to act as pollinators for the Weschcke, which is devoid of pollen.[33] This year particularly, the difference in rate of growth between two varieties grafted on the same stock was very apparent; in every case all other varieties greatly exceeded the growth of the Weschcke hickory, but in many cases, only the Weschcke hickory had any nuts growing on the graft, and if there were any nuts on another graft, there were but a few. In practically all cases, the diameters of the scions of varieties of hickory other than the Weschcke were at least twice the diameters of the Weschcke grafts, and the growth of all varieties so grafted was healthy and vigorous and thoroughly compatible with the native bitternut hickory root system.
Several years ago I had to trim some of these other varieties back in order to allow the Weschcke graft to get more growth because it was so backward in development that it looked as though it might be crowded out of existence. It never occurred to me in those years that it was the difference in rate of growth between the two varieties which was really responsible for the difference in the diameter of the scion growth, and not some accident of propagation. Now it is very apparent, from the many examples that I have about me, that the Weschcke hickory is about one-half as fast a grower as such varieties as Bridgewater, Deveaux, Laney, Siers, and many others. This, then, accounts for the heavy bearing of the Weschcke when it starts to bear on the bitternut roots, and it also explains the lack of bearing in such varieties as Beaver, Fairbanks, Laney, Siers, Pleas, Deveaux, Rockville, Green Bay, Hope pecan, Stanley shellbark, Platman, Kirtland, Glover, Barnes, and many others which are hardy and get along well with the native bitternut root system, some of them having lived more than fifteen years grafted in such combination. The Bridgewater is the only variety which bears a fair crop of nuts as compared to the prolific Weschcke, and is the pollinator for the Weschcke when used in orchard planting.
[Footnote 33: See author's added remarks following.—Ed.]