Established magnolias usually do not require regular pruning; generally they do not respond well to pruning. But where damaged branches or overgrown specimens need work then this should be done when the tree is in full leaf, usually during midsummer. Pruning cuts made at this time of the year will have plenty of time to begin healing before the onset of winter, and are less prone to dieback.
Selecting branches
On overgrown plants, do not trim back all round, but rather select the highest- or widest-growing branches to remove, which will reduce the overall height and spread.
Taking out whole branches or side branches maintains the graceful shape of these trees and shrubs. However, while deciduous magnolias such as M. campbellii, M. x soulangeana and M. stellata have good powers of regeneration, large cuts into old wood are best kept to a minimum.
Magnolias can prove slow to heal and new growth is frequently not made until the second season after pruning. With vigorous species however, pruning may be followed by the production of strong, upright growing shoots known as water shoots. If possible, rub these buds out before they shoot,or alternatively, prune out this growth as soon as possible to prevent them spoiling the eventual overall shape of the tree.
Summer is also a good time to cut back or remove any wayward shoots on wall-trained evergreen Magnolia grandiflora.
Tony Dickerson