Dormant and Summer Pruning Compared by Pruning Young Apple Trees Once on a Succession of Dates

Rooted cuttings of Malus sylvestris (L.) Mill. var. M.VII were permitted to grow from a single shoot. This was cut back to 3 cm. and the utilization of the subsequent increment, as leaves, stem and root, was determined. Different batches were treated on 7 occasions–June, July, August and December of the 1st year of the bud’s growth and March, April and June of the 2nd year. Also two further batches were cut back in the 2nd year (June and July) to the base of the 2nd year’s shoots. The growth to the end of the 1st and 2nd years was compared with that of unpruned controls.

In most cases pruning reduced the subsequent increment. Following dormant pruning (December, March, April) this reduction was associated with fewer growing shoots, although the leading shoots might be longer than comparable shoots on the controls. The reduction in increment after pruning leafy shoots was attributed to the loss of leaf and to shortening the effective growing season. Such leafy pruning was equivalent to the loss of ½ to ? of the growing season.

The relative distribution of increment (i.e. increment of the part as a fraction of the total increment) to leaf, stem and root was little affected by pruning. The main effect of pruning occurred within the stem region, where the fraction utilized by the old stem decreased, and by the new stem correspondingly increased, so that the total stem fraction changed very little. A small effect following pruning leafy shoots was that the leaf fraction increased slightly and the new stem decreased.

It is concluded that the different effects of dormant and summer pruning may be attributed to the relative importance at different times of the year of bud inhibition and curtailment of the growing season.