Driving home yesterday morning I noticed once again the number of crews out and about pruning trees. I paused for a few moments at one site and watched as within minutes a mature, well-shaped, shade-giving mesquite was reduced to one scrawny, crooked stick with a little tuft of branches way up on top. The crew started the job standing in nearly full shade and by the end they were standing in full sun – without even moving.
We seem obsessed with pruning trees around here.
Pruning trees is the one area of desert landscaping where landscape maintenance companies and homeowners most often make mistakes, and the biggest mistake we make doesn’t start with “how” we prune, but with “why.”
Common practice, especially among those who are paid to prune trees, is to treat tree pruning like getting your teeth cleaned at the dentist: do it twice a year whether you need it or not. But the truth is, tree pruning is more like surgery: you should only do it when you really need it. And, no, cosmetic surgery doesn’t count.
To understand why, keep a few things in mind:
Any time we prune a tree we damage it. Trees, like humans, are protected by a skin – bark, in the case of trees – that helps to exclude diseases and parasites. Every time we prune a tree, we open a wound in that skin, making the tree susceptible to insects and pathogens.
Trees, unlike humans, make their own food. While we can provide a tree with water and fertilizer, those don’t feed the tree. Trees make their own food in their leaves, through the process of photosynthesis. Any time we prune a tree, we prune off leaves, or leaf-producing twigs, and reduce the amount of food that a tree can make for itself. Too much pruning, and the tree goes into stress because of a lack of food.
Trees that are pruned too much become weak, grow poorly, and never develop the strong trunk and branch structure that makes for a sturdy, safe, and strong tree.
Trees provide specific and measurable benefits in the landscape, including shade, heat reduction, dust reduction, and more. They also add a calculable monetary value to a property. Whack a tree into a funny shape and you get none of that.
Trees that are over-pruned or pruned incorrectly can and do become a legal liablity. If a tree is pruned in such a way that it consequently fails and damages life or property, the tree's owner may be legally liable for damages.
And, lastly, you have to pay someone to prune your tree; isn't it worth your while to make certain you're spending your money on something you need? If you've got excess cash, send it to the orphans.
So, what are good “whys” for pruning trees? There are really just two: to remove dead, diseased, or injured wood, and to keep your tree from being a nuisance.
"Nuisance" does not mean, "Look, that darn tree is growing again." That's not a nuisance; that's what trees are supposed to do. "It's getting too big," doesn't cut it either; you need to finish the sentence: getting too big for what?
Obscuring traffic, interfering with your roof tiles, making the sidewalk impassable; those are good reasons to prune a tree. If your tree is getting into the power lines, that's an excellent reason to prune a tree; call the power company and they will do it for you, safely and for free.
Before you have your tree pruned, ask yourself: why? If you don't have a good answer, then don't do it. You will have a cooler, shadier, safer, and less expensive landscape.