Pruning Overview
Trees invented tree care hundreds of millions of years ago and have done a great job of it without us until relatively recently. In fact, trees even self-prune. So trees do not categorically need to be pruned or cared for.
That said, trees evolved in enclosed, dark forests and we plant them in open landscapes. This mismatch between the conditions they've evolved for, and the conditions we put them in, allows trees to grow in ways they wouldn't otherwise. Check out the habits of the trees below, growing so differently simply because the ones on the left are competing with one another in the forest environment (scrambling upward for light) while the one on the right is open-grown:​
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This open-growing environment can lead to various vulnerabilities, some of them structural. Almost every open-grown tree would benfit from early structural pruning to head off the worst of the common structural issues.
With respect to establishing a tree's permanent architecture and structural integrity, pruning a tree early in its life can save tons of time and money down the road. (More on that later).
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​We also have all sorts of aesthetic prefences, from wanting more light, to preferring particular styles, to wanting to encourage flowering, etc. Below are examples of a gradient of styles from formal to semi-formal to naturalistic - just a few of many styles:​​
When we were Arborists at Brooklyn Botanic Garden visitors would often ask us how to prune a tree. Despite practicing and teaching Arboriculture daily, we'd be paralyzed by the question, often responding with "how much time do you have?!". It's a bit like encountering a doctor on the street and asking in passing how to practice medicine. Pruning involves so many different variables that you could start almost anywhere. ​Here - in no particular order - are some pruning considerations:
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​overall objectives;
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tree risk potential;
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how trees make, move and store energy;
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how trees respond to wounds;
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particulars of different tree species;
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seasonality;
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pest and disease concerns;
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pruning styles - formal, informal, naturalistic, Japanese, etc.;
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site constraints;​
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budget;
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service interval;
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tree age/vigor;
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existing tree architecture;
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multiple vantage points
​A great Arborist will never stop getting to know each type of tree they come across and how they relate to things like climate, compaction, pests and diseases, light levels, pollution, etc. So ideally an Arborist will walk up to trees with something like this in mind:
Then step back and try to see each tree for the incredible idiosyncratic wonder that it is:
Holdinging all of these things, a vision and direction will begin to emerge. This will lead to scores of individual decisions. Add to that, years of practicing the physical techniques required.
That's how to prune a tree.