This advice is suitable for open-grown ornamental trees.
Although pruning does make trees slightly smaller than they
would be without pruning, attempting to keep a big tree small by
pruning is usually unsuccessful. This advice does not apply to
restricted tree forms such as fans and espaliers. When to prune
trees Deciduous trees (ones that lose their leaves in winter)
are usually pruned in autumn and winter. In some cases, for
example with magnolias and walnuts, pruning is best done in late
summer, as healing is quicker. Trees such as Prunus sp, which
are prone to silver leaf disease are best pruned from April to
July when the disease spores are not on the wind, and the tree
sap is rising rather than falling (which pushes out infection
rather than drawing it in). Some trees can bleed sap if pruned
in late winter and early spring. Although seldom fatal, this is
unsightly and can weaken the tree. Birches and walnuts often
bleed if pruned at the wrong time. Evergreens seldom need
pruning, although dead and disea