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.
136. The object of this operation is to remedy any bad results of winter-pruning, of pinching, and of omissions in the disbudding; also to concentrate the sap in the tree, by removing those useless productions which would have to be cut off at the winter-pruning, and which, meanwhile, would have fed on the sap at the expense of others necessary to be preserved.
137. Summer-pruning, which is performed with the secateur, or with the pruning-knife, as may be requisite, is less applied to the wood-branches than to the fruit-branches, especially when the winter-pruning is well done. The following, however, are some circumstances where it should be employed. When the extremity of a vigorous young shoot has been too severely pinched, the upper eyes usually open at the same time, and several laterals are formed causing great disorder. These are perhaps pinched in their turn, and very often the result is a crowd of young shoots, originating near the same point. Such agglomerations receive the name of willow stools; they consume a great quantity of sap, and tend to impoverish the neighboring shoots. In this case, all these injurious shoots must bo cut down to one of the lowest and weakest laterals; and the growing-point must be pinched before there is time to form eyes along the shoot. The consequence is, the sap, finding all outlets at this part temporarily closed, turns into other channels before the former can be re-opened.
138. The removal of any shoot, and particularly that made after the second growth, of August, when the base of the shoot becomes woody, is in fact a summer-pruning.
139. It often happens, in the square form of training, that the upper secondary branches of a completely formed tree make two strong growths in the early part of the growing seaoon, notwithstanding the pinching of their terminal shoots and their laterals. In such a case we must cut back to a weak lateral, which then becomes a fresh leader.
140. With regard to the other wood-branches, it is only in case of accident to their extremities, such as breakage by the wind, severe disease resulting from gumming, or from any other cause injuriously affecting the leading shoot, that we must prune back in summer to a lower shoot suitable for succession. In doing this, we must take into account the position of the branches, and their relative force, so as to choose one more or less vigorous, which must afterwards be treated according to circumstances.
141. Summer-pruning is to the fruit-branches what disbudding is to the superfluous shoots. It sometimes happens that, deceived by appearances, we retain some fruit-branches which eventually do not realize our expectations, and which would otherwise have been cut off; they must be cut down on the young shoot nearest to their base, in order to get rid of the useless wood, and to encourage the growth of this young shoot, which is intended to become a fruit-branch next year. This suppression prevents a useless absorption of sap, and it not only prevents confusion, but likewise admits a freer circulation of air. It is also at the summer-pruning that the extremity of the successional shoot is cut down on the lowest lateral of those induced by pinching. In this respect summer-pruning is very important; for it concentrates the sap, and greatly benefits the part retained, which, in consequence, becomes furnished with wood and flower-buds (126).
142. It also often happens that a fruit-branch of the first sort (77, 78,) has been left longer than desirable, in order to prune in winter to a wood-bud; and which fruit-branch at that time had not a pushing-eye at its base, but has since produced one. In that case although the fruit-branch may be in bearing, we cut it back to the young shoot at its base, in order not to lose the opportunity of thus obtaining the successional shoot.
143. Summer-pruning is performed according as it is found necessary, and every time the shoots are nailed in during summer, until after the fruit has been gathered. The more it is attended to, so much the more is the winter-pruning advanced.