Summer pruning and pinching interferes with the growth by extension, and threatens the very life of the tree; the entire removal of all new shoots and their foliage, and the removal of the successive attempts by the tree at their reproduction, will cause its death in a little while. Their partial abstraction, as practiced in summer pruning and pinching, being an attack of the same kind, results in the formation of fruit-buds. The operations of budding and grafting upon an uncongenial stock, interrupting the circulation by ringing, by ligatures, by hacking, twisting, and bending downward, all tend to check the growth by extension, and are attended by similar results, since they are antagonistic to the mere production of wood. Shortening-in the branches of some species, which form their fruit-buds upon the shoots of the current year, has the effect to give them a fuller development, if performed during the summer, but if deferred until the following spring, it will have the directly opposite result, and will cause the production of woody shoots at the expense of the fruit.
The season for pruning has been made the subject of much discussion, and different periods have been very confidently advised by different authorities, from which it may safely be inferred that all are somewhat right, or may be supported by good reasons. This refers of course to pruning in its general sense, of trimming, and applies to the removal of limbs of greater or less size. We always desire to avoid the removal of large limbs, and should endeavor to provide against the necessity of such removal, by trimming our orchards sufficiently when they are young, and while the branches are small; but when such removal becomes absolutely necessary, it should be performed late in the autumn, when vegetation is at rest, because it is found that such large wounds, which cannot be soon healed over by the new growth, will at this season dry in, and resist the action of the elements better than if the section had been made when the wood was full of sap in active circulation.
Early spring is a favorite period for pruning, chiefly because it is comparatively a period of leisure; the weather is less inclement than in winter, and the absence of foliage affords us an opportunity to see our work and to anticipate its effects upon the tree. So soon as the buds begin to swell and the foliage to expand, pruning should be arrested, unless in small trees, because the sap is in active motion, and the material called cambium is not yet developed, hence the wounds will bleed, and are not so readily healed over; besides, the bark at this season is very readily separated from the wood, and bad wounds are thus frequently produced by the pruner, which may seriously damage the tree. Then follows a period when pruning had better be suspended until the time that the trees have completed their growth by extension, and formed the terminal bud at the ends of their shoots. The date cannot be given, but it is sufficiently indicated by this mark in nature's calendar; the formation and full development of the terminal bud, and by the copious deposits of woody matter throughout the tree. The annual layer of fibres is then being produced, and the tissues are in the formative stage; the tree now possesses within its own organism the best of all plasters to cure and cover the wounds made by the saw and knife, now the tree possesses the true vis medicatrix naturæ in the highest degree.
A few intelligent nurserymen have learned this very important lesson, and have applied it in the preparation of their trees, for the exposure incident to their removal from the nursery to the orchard. A very few practice it systematically; I knew one, (alas, for the lamented Beeler, of Indiana), who acted upon the suggestion made to him by observations and experiments in vegetable physiology. He left the side branches, though subordinated by shortening when necessary, in order to give stocky stems to his trees, and then removed them with the knife during the summer before they were to be sold and planted, instead of waiting until they were dug and sent to the packing house in the fall or spring. The result was, that while his stems were stout and stocky, they were also smooth, the wounds neatly healed over with new bark, instead of being open from the fresh cuts and liable to crack or bleed, as they would have done had this pruning been deferred until after digging, either in the fall or spring. This may be considered a small matter, but it is an illustration of the principle involved in selecting the period for pruning.
For the removal of small limbs from young trees, hardly any time can come amiss—better to do it out of season than to neglect it, and it is a good rule to have a sharp pruning knife always at hand when passing through our young orchards. There is but one time when pruning is absolutely interdicted, and that is when the wood is frozen. When so circumstanced, it should never be cut nor disturbed in any manner—not even to gratify your best friend, by helping him to a few grafts from your proved tree of some coveted variety. Let him wait for a thaw, or go away without the grafts, rather than commit such an outrage upon your tree: as to approach it with a knife when frozen.
While considering the question of the proper season for pruning, there is one axiom of great importance which should be firmly impressed upon the mind of the orchardist. Much will depend upon which of the two leading objects, above indicated, he may have in view—vigor of growth and symmetry of form, or simply fruitfulness, as the result of his labors in pruning his trees. Pruning at one season will induce the former result, at a different period of the year the same work will conduce to the latter; hence the postulate Prune in winter for wood; in summer for fruit.