Buds: Buds of the walnut are in vertical groups of two or three in the axils of the leaves. They have few scales. They appear on seedlings and current year branches. Some have short stalks. If broken off they do not usually grow back again. The second year, these buds usually drop off in mid-season. In cutting off buds, unless the group of buds is taken out as a chip, some may grow out again.
Leaf arrangement: There is a three rank arrangement of leaves in the walnut, the ninth leaf coming in the same position as the first. According to the work of Caesalpino, the buds should then rise in three places at the crown. Only in rare cases does this occur in the black walnut, although it is usual with the Persian walnut. If the nut is planted deep this causes much suckering and a tendency to etiolate the buds so they will stand water.
Buds are sensitive: Buds are sensitive to water, and storage material must be fairly dry and cool. In two large boxes of scions received last year from Germany, some 20 varieties of Persian walnut, all had dead buds when received. They were packed in German peat. When buds are covered with wax the wax must not be too hot or it will kill the buds. In placing grafted walnuts in sphagnum or sand they should not stay wet or the buds will die. Either unions must be above damp sand or sphagnum, or the buds be protected by wax or adhesive.
Sap: In spring grafting there is an enormous flow of sap which will sometimes tear the plates out of the pith. Grafts may be protected by girdling the stock a few inches below the place where the graft is set, or both above and below it. In 1937 259 walnuts three years old were cut off six inches above the ground and girdled two inches above the ground. 171 crown buds came up, 88 started above the girdling. 207 trees were cut off three feet above the ground, and the trunk girdled six inches above the ground. 153 started above the crown, and 90 started above the girdle. The same year (1937) 195 trees three years old were cut off four feet above the ground, and all buds above ground were cut flush with the surface of the bark. This was repeated twice, finally taking buds out as a chip, except the top bud; 126 died; 69 grew from the top but. 203 trees three years old were cut off five feet above ground and all buds cut off except upper one; 64 died; 139 grew from top bud. 200 trees three years old were cut off six feet above ground, and all buds kept rubbed off except top one; 33 died, and 167 grew from top bud.
Vitality and sap: Black walnut sap changes color from oxidation almost instantly. Bench grafts must be made quickly and put in place at once or the unions will dry out. If the root does not stain hands in grafting the graft usually fails. In outdoor grafting if the sap stands in pockets the sugar will ferment, killing the graft. There is a new Jersey (3) bulletin which shows black walnut sap as unstable, quickly forming sugar when exposed to warm weather.
Vegetative propagation of greenwood cuttings: Witt and Spence (4) in England working with greenwood cuttings attained 75 per cent success with Persian walnut and Royal walnut in July and August. They had no success with black walnut at that time (1926). The Germans in 1936 (1) working on greenwood cuttings had most success with the Persian walnut, but used greenwood taken in September.
Vegetative propagation or hardwood cuttings: In 1938 the author (2) using growth substance on saddle grafts of various walnuts found Asiatic and western walnuts went on their own roots. At this time the Tasterite black walnut went on its own root. In 1946 and 1947 using about 25 varieties of black walnut, Persian, western and Asiatic walnuts, eight inch hardwood cuttings were used beginning in December and repeated in the spring of 1947. Nearly all the cuttings of the larger size (about ½") started in about a month and grew about two months. Then all died. There were balls of callus on many of them. One on Thomas was an inch in diameter. The bottom heat was held at 70 degrees F. This may have been too high, as on raising the cuttings it was found the callus had rotted. This procedure has possibilities.
Literature Cited
1. Institut fur Obstbau, Berlin. Die Walnusz veredlung. (Vegetative propagation of walnuts). Merkbl. Inst. Obstb. Berlin 5, pp. 15, 1936.
2. Lounsberry, C. C. Use of Growth Substance in Bench Grafting Walnuts and Hickories. Northern Nut Growers Association 1938 Report, p. 63.