Ask a Gardener (January 2021)
Updated: Feb 12
When is it Best to Prune Trees?
by Helen Hartung
The short answer is in winter. This holds true for many, if not most, trees in Southern California, especially evergreens, such as pines, cedars and ficus.
There are exceptions.
--Southern magnolias, though evergreen, should be pruned after they bloom, usually in early spring.
--Flowering trees should be pruned after they bloom. For most flowering trees, such as jacarandas and ornamental plums, this is in spring. Pruning later in the year will result in fewer blooms next time. Late flowering trees, such as crape myrtles, should be pruned in winter.
--Most deciduous trees (those that lose their leaves in fall) should be pruned in winter. Exceptions include maples and birches, which release a lot of sap if they are pruned in winter. They do better in spring.
--Fruit trees, including citrus, have their own requirements. It’s best to consult an expert.
Avoid pruning in the heat of summer (too stressful) and in early fall, when certain wood-decaying fungi proliferate.
Good pruning should be subtle and respect the natural form of the tree. Magnolias, for example, should be full and pyramidal in form, not trimmed like a poodle. Over-pruning will damage a tree, impeding photosynthesis and encouraging disease and insect infestations. If the tree “needs” to be heavily pruned regularly (for example, to let in more light or open a view), it is the wrong tree for the location.
The best rules for tree trimming are:
1. Learn what your trees are supposed to look like, and love them for what they are. Don’t try to force a southern magnolia into an airy, open shape, and don’t cut the top off a tall sycamore or liquidambar.
2. Most important! Hire a licensed arborist for all your pruning, and recognize that some trees need to be pruned at different times than others. Do not trust your precious trees to a cheaper, untrained crew. You get what you pay for.