Hard-pruning and formative pruning should be carried out in autumn after leaf-fall, preferably within a 2-week period, or during the mid-summer semi-dormant period when wounds can heal very quickly. Never prune your maple during spring, as all Acer species have a habit of bleeding profusely, which can severely weaken the plant or even result in the loss of branches. Ensure all wounds are sealed.
Note: For trees that are displayed for their bare winter silhouettes, summer pruning might be considered.
Unless growth is required to form new areas of foliage or branches, cut new growth back to one or two pairs of leaves following bursts of growth through the growing season. For trees that require short internodes, buds can be pinched out, leaving 2 new opposing leaves as soon as they are visible; this will produce fine, twiggy growth with short internodes and also promote back-budding. Remove all growth with long internodes.
Leaf-cutting can be carried out in mid-summer. This results in smaller leaves, better ramification, and stronger autumn leaf colour. However, defoliation should only be carried out on healthy trees, never in the same year as repotting, never 2 years running, and never on weaker red-leaved varieties.
For highly ramified Japanese maples, ensure that enough light can get into the canopy by removing one of each pair of leaves. For trees that are displayed for their bare winter silhouettes, summer pruning might be considered.
Wiring can be carried out at any time from early spring to late autumn, though each period carries its own advantages and disadvantages. Optimally, wiring should be carried out on bare branches before bud extension in spring, after leaf-cutting in mid-summer, or after leaf-fall in autumn. At these points in the year, the branch structure is not obscured by foliage, and there is enough sap remaining in the branches to keep them supple.
Spring wiring should be carried out with great care, as the new buds can dislodge very easily, and wire can quickly start to mark the bark after the rapid growth of spring. Trees wired after leaf-fall in autumn should be protected against heavy frosts, as branches will not heal properly until the spring growth period. During the winter, branches become exceptionally brittle and can snap without warning; only very gentle wiring should be attempted.
