Walnuts have been grafted in pots in the greenhouse at the Experiment Station at Geneva, N. Y. for a dozen years or more and the practice is successful and very useful. This method was adopted for two reasons. First: Under field conditions results are often uncertain, owing to the vagaries of the weather or neglect at a critical time. The inexpertness of the operator made it desirable that the work be done under as favorable conditions as possible, with the hope that a favorable environment might overcome in part the lack of skill. Second: The work can be done in March before the field work begins, whereas field grafting in May would often not get done owing to the pressure of other work at that time. This method is not original with the writer, but is similar to the method used at the East Malling Research Station in England and described by Witt in 1928 [1].
The rootstocks, two year old black walnut seedlings raised from nuts planted in the nursery, are dug in the fall, stored in the nursery cellar until late February or early March, at which time they are potted in six or eight inch pots, depending upon the size of the rootstocks. The roots are cut back so that the plant will fit in the pot. At this time the tops are cut off, leaving the stem about 8 inches high. The pots are placed in a warm house, watered as needed, and in about 10 days the buds begin to break.
The Jones modified cleft graft is used. The stub is cut off at grafting time and the cleft is made by cutting, not splitting, the stock with a large grafting knife. The scion is tied in place with nursery tape, half-inch size, with a short wick leading out of the cleft. The scion is painted with grafting wax.
+Care of the Grafted Plant+
The pot is set in a propagating frame about 18 inches deep, with bottom heat, and covered with glass, plus lath or cloth shade. An inch of peat in the bottom of the frame is desirable, to hold moisture and maintain high humidity. The temperature of the frame is kept in the eighties, but is not allowed to go above 90°F. Under these conditions of warmth and high humidity, growth activity is rapid and in about two weeks the buds break, although, some may not start for a month. This spring adventitious buds developed on several scions. Many suckers arise from below the graft, and these are rubbed off two or three times a week. As soon as the shoots from the scion are two or three inches long the plants may be removed to a cooler house, where there is less danger of overheating on hot spring days. Later, they go to the cold frame for hardening off, and when danger of frost is over after May 21st, they are set in the nursery for two years. First year growth is not over eight or ten inches, but the second year the plants grow to three or four feet or even more in a favorable season.
The percentage of grafts starting depends largely on the scion wood. Wood cut from vigorous young trees which is grafted the same day will give a 90 percent stand or better, but wood from other sources varies according, to the age and vigor of the tree from which it is cut and the percentage of success may be much less.
This method is useful for small scale operations where a greenhouse is available and it is desirable to do the grafting before outside work interferes with it. For one not skilled in nut tree grafting success is probably more certain than with nursery grafting.
+Literature Cited+
1 Witt, A. W. The vegetative propagation of walnuts. Ann. Rpt. of the East Malling Research Station 14th and 15th Yrs. 1926-1927 II Supplement pp. 60-64.
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