This section is from "The Horticulturist, And Journal Of Rural Art And Rural Taste", by P. Barry, A. J. Downing, J. Jay Smith, Peter B. Mead, F. W. Woodward, Henry T. Williams. Also available from Amazon: Horticulturist and Journal of Rural Art and Rural Taste.
62. The name of winter-pruning is given to the principal pruning, because it is generally performed at that season. As for us cultivators, who have a large number of trees to manage, we have no fixed time of pruning. I have occasionally pruned some of my trees in December, with the same result as those that were pruned later. It may therefore be concluded that it can be done from January till April: but I recommend it to be done soon rather than too late; for when vegetation is active, pruning causes a more sensible reaction on the trees. There are, however, cases where late pruning may be of use. When a tree not yet growing is pruned, it loses no sap; for on the latter beginning to circulate, it flows to the buds, which, by expanding, afford it an outlet; at the same time the cuts are so far dried up as to offer a sufficient resistance to the escape of the sap. If, on the contrary, we prune when the sap is actively circulating in the tops of the shoots, their pores, opened by the cuts, allow a portion of it to evaporate. Whence the conclusion, that it is proper to prune old trees when the sap is down, because they have none to spare; and that, on the contrary, it may prove beneficial to prune young or very vigorous trees after the sap has risen.
The loss of a part of this fluid can not be disadvantageous to them; for, by moderating their vigor, it insures the production of fruit. We must not forget that fructification weakens the trees. One of the objects of pruning is to diminish the superabundant strength of a tree; and when once it has put it in a state for fruit-bearing, pruning maintains a due balance between the production of wood, and that of fruit, so as to economise the strength of the tree, and insure its prolonged existence. Since I have been a cultivator, I have had numerous opportunities of convincing myself, by experience, of the correctness of this observation.
63. To render the operations of pruning more intelligible, I shall consider it in two points of view: 1st, the pruning ot wood-branches; 2d, the pruning of fruit-branches.
64. 1st, Pruning of the Wood-branches. Its principle is a consequence of their natural organization. I have explained (19 - 26) what is a shoot, and what is a branch. The first, which ultimately becomes the second, is furnished throughout its length with wood-buds, or with shoots of large or small size; and is always, itself, terminated with a bud which is designated by the name of terminal bud, or eye, or growing-point. The sap, which tends to rise in all trees with great force, but more especially in the Peach, gives a greater development to the terminal bud than to the others, which become gradually weaker in proportion to their distance from the top of the shoot, and as they come nearer to their origin at the place of the last pruning. The result of this constant natural tendency is, that we can direct the sap to whatever lateral bud we please on that shoot, by cutting the latter at a very short distance above, to make a new terminal bud, or eye, which takes the name of ceil terminal combine, to distinguish it from the natural terminal eye, and because the effects of pruning are combined in its development.
It is a bud, or eye, rendered terminal by pruning.
65. Thus the shortening of branches has not the effect of stopping their growth, but that of giving a great vigor to the eye above which the cut is made; and to the lower buds a strength which varies according to their distance from the bud to which the shoot was cut back. This bud, in growing, forms a shoot which constitutes a new prolongation, terminated by a growing-point; and is furnished, in turn, with lateral wood-buds.
We now perfectly understand that, as we can make any lateral bud a terminal one, by pruning above and near it, we can choose it according to our requirements and the end we have in view.
66. This is the fundamental principle of pruning the wood-branches. They should be pruned long or short, according to the strength of the tree. In those that are vigorous it is not uncommon to see branches make shoots of from four and a half to six and a half feet long in one season, and sometimes even of greater length. In such cases it is well not to prune them short, because, by leaving them at considerable length, there is space for several shoots likely to be produced of medium strength for furnishing the branch. This is a better mode of subduing the impetuous growth of young trees, than that of delaying the pruning till such time as the wood and flower-buds commence to open, and thus cause a loss of sap as mentioned (62). Moreover, I have only spoken of late pruning in order to meet a case where, from some cause, the operation could not be performed at its proper time; and it should be understood that, under these circumstances, it is the youngest and strongest trees that suffer the least from such delay.
67. If, on the other hand, short pruning is adopted, it will produce strong young shoots, often too near each other, the vigor of which can neither be repressed by pinching, nor by any other operation. There would be no resource left but to cut them out at the following pruning. This increases the number of wounds, weakens the tree, and prevents it from assuming a regular form, with branches tapering uniformly from their bases to their extremities.
68. Therefore, short pruning must not be adopted, except on the wood-branches of feeble trees. It is advisable in this case, because it would be improper to give them a greater length of wood than they can nourish; and because it is desirable that branches should have a thickness in proportion to their length. In cases like these, short pruning concentrates the sap, and the branch thus pruned becomes thicker. When ultimately such a tree takes a more active growth, the shoots, when pruned, must accordingly be left at greater length.
69. The Peach tree, trained in the square form, is first set off with two main branches (branches meres); and, in order that its form may be complete, each of these must be furnished, on its under side, with three secondary branches, which are called lower; and on its upper side with three secondary branches, called upper.