In the Garden:
Northern California Coastal & Inland Valleys
Dead twigs, crossing branches, and the inability for light to penetrate to the interior are all results of topping a tree.
You've seen them, especially under power lines and near overhanging structures: trees that have had their heads chopped off to accommodate an overhead obstruction. Topping seems like a good idea at the time, but it's extremely hard on the tree and takes years to correct.
I had the opportunity to work beside a professional tree trimmer who was trying to guide a Douglas fir back into a reasonable shape and size. The tree had been topped by the homeowner to create a bonsai effect outside of a bedroom window. Douglas fir, when left alone, will grow a single trunk and head 50 to 75 feet straight up. This poor tree had been coaxed into a twisted, twin trunk.
Nature has a curious way of curing our mistakes, and in this case the tree was trying very hard to grow a new leader (the main growing tip of an evergreen tree). There were at least 7 new vertical branches growing off the bushy top of the tree, not to mention the tangled mess of growth, fallen needles, and dead wood that blocked all light to the interior of the multiple trunks.
The tree trimmer gave the homeowner two options: remove the tree (which the owner wasn't willing to do), or maintain the tree on a regular basis in the existing bonsai shape. The latter option will require constant pruning and thinning (expensive and time-consuming).
Hedge shears in the hands of an inexperienced gardener can be dangerous. It's natural to try to keep plants low by pruning to preserve a view or steer clear of overhead wires. A better solution is to select a variety of tree that won't grow tall in the first place. Always do your homework before planting a tree in your landscape.
The Sunset Western Garden Book provides all the information necessary for planting every type of tree, shrub, and plant suitable for our climate, including information on how tall they will grow. The correct way to reduce the height of a tree or shrub is to selectively prune out 20 percent of the unwanted tall growth. This will allow light to enter the interior of the plant, forcing new growth on the lower branches. The following year, or even later in the same season, remove another 20 percent. The secret is to gradually remove the unwanted growth so that you don't get the "hat rack" or "cat head" condition of crossing branches and woody stubs. The tangled wood left behind from a bad "haircut" is an invitation for insect, fungus, and disease problems, not to mention the fact that it's ugly.
In Menlo Park there are boulevards lined with mature native oaks that have been selectively pruned to make allowance for overhead power lines. The trees have been professionally groomed over many years to spread their crowns in a "Y" shape so that the wires can run unhindered between the branches. It's an excellent solution for both the trees and PG&E.
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