Shade trees in Bakersfield have a range of appearance, from the pleasing to the grotesque. Unlike fruit trees, pruning for shade trees, usually done in autumn, should not be considered an annual necessity, especially if structure has been established when trees were young. We recall that trees in the world’s forests grow well with no pruning intervention and severe pruning is damaging to most tree species.
So the first question to ask before pruning is, “Why?”
Pruning should proceed only if specific reasons exist and clear goals have been established, such as the following:
Structure: Shade trees should have a central leader with scaffold branches spaced one to three feet apart. Branches should have wide angles of attachment to the trunk to lessen the likelihood of splits as the tree grows. Competing branches should be removed. Establish a dominant leader by shortening competing leaders, especially in young trees. That’s easy to do in some tree species, like liquidambar, and more difficult in others, like Chinese pistache.
Health: Diseased, damaged or rubbing branches should be removed.
Safety: Branches which pose a hazard should be removed. Examples are branches which hang low over sidewalks.
Appearance: Many trees have interesting trunk and scaffold forms. Exposing the form of the tree can enhance its appearance. Trees that have been pruned correctly retain a “natural” appearance and often don’t obviously look as though they have been pruned.
Two types of pruning cuts, heading and thinning cuts, should be used in combination. A heading cut shortens branches and removes the terminal bud. If the terminal bud or shoot is removed, lateral buds will break and lateral branches will grow faster, therefore, bushy growth results. Heading main branches to the same point every year, as is often done with mulberries, is known as pollarding. Pollarding dwarfs trees and limits shade and some species can be killed outright by this practice.
A thinning cut removes a smaller branch at the place of attachment to a larger branch. Thinning opens the tree crown while retaining larger limbs and preserves a “natural” appearance of the crown. Keep the central leader and key structural branches to preserve a framework within the tree crown.
When a tree is topped, several lines of defense are breached, and direct entry to the heartwood of the tree is possible for decay fungi. Therefore, topping should be avoided unless absolutely necessary. If severe topping is necessary, perhaps tree removal is a better choice followed by replanting of a smaller species. ￼
John Karlik is an adviser with the University of California Cooperative Extension in the areas of environmental horticulture and environmental science. He has been with UC Extension at its Kern County office, 1031 S. Mt. Vernon Ave., Bakersfield, for 33 years.