Cole Hardware's Hotline: Pruning Trees and Shrubs


	Only the last illustration is the correct way to make a cut. The others will interfere with the healthy growth of the bush or shrub.

Pruning Trees and Shrubs

(It's that time of year again ...)

Rule of Thumb #1: Flowering, fruiting and growth habits differ widely among trees and shrubs. These differences impact pruning strategy and technique. Learn about your tree/shrub before you get your pruning shears out!

Rule of Thumb #2: Be clear about why you are pruning. The most common reasons are esthetic form, structural strength, health (of the tree/shrub) and compatibility with other elements in the environment.

Esthetic Form

    The core esthetics questions, taste and tradition, are matters of context and personal choice.

    Pruning is like cutting hair: Do a lousy job and you’ll have to wait quite a while to try again. However, how you prune woody vegetation greatly influences future growth patterns ... so to a greater extent, what’s done is done.

    Take your time! Think about what you want your tree/shrub to look like down the road and work with its natural growth patterns. Unless you are working under very controlled conditions, the eventual results will fall somewhere between what you visualized and how the tree grew given its natural character and the limits of the environment.

    The most Neanderthal of pruning activities is called "topping" -- that's when the whole top of a tree is lopped off. The reasons for topping are various: to eliminate interference with views or overhead wires, to reduce root growth (the efficacy of topping for this purpose is questionable) or to achieve a particular esthetic end. Topping shortens the life of a tree (provides multiple points for insect and disease invasion), and is self perpetuating (encourages suckering). In many cases topping is a last ditch effort to make up for a lack of foresight. Everything (except the crew cut look) achieved by topping is better achieved over time by planting the right tree in the right location, taking existing trees into account in the early phases of architecture and streetscape design, and taking a long-term approach to pruning.

Structural Strength and Health

    Left to its own devices, vegetation goes through its own natural pruning process -- weak and crowded branches break off or die and remain as dead wood within the living structure, creatures gnaw and infest. The intent behind getting your loppers out is to intervene early in those natural processes and bend the natural growth patterns to your wishes. On that note, keep in mind: Tight branching angles weaken the structure.

    Crossing branches tend to rub and create an entry point for insect and disease. Dense branching limits air flow and light access. Multiple leaders (trunks) fight for predominance (one of them will eventually break or die off, inviting insect and disease invasion and throwing the whole structure out of esthetic balance). A good pruning cut doesn’t leave a big stub but also doesn't interfere with the collar of bark that grows at the union of two branches (both extremes would invite insects and disease).

    A very general rule of thumb for trees and shrubs is to remove no more than 25% of the live growth. Your particular tree/shrub and situation may well require you to break this rule, but keep in mind that with each cut you are reducing the plant’s capacity to feed itself (via photosynthesis) and with each additional cut you increase the plant’s natural hormonal response to send out a burst of new growth. A real hack job may result in wild “sucker” growth during the next growing season (suckers are shoots of rapid growth and are thus weak and esthetically incompatible with the overall structure of the tree or shrub). That means you’ll have lots more pruning work in the following seasons.

Compatibility with Other Elements in the Environment

Elements that are likely to influence your pruning decisions include buildings, walkways, wires, views (good views you want open or bad views you want screened) and other vegetation. Weigh all the elements in your mind (try the exercise in the box below), factor in time and then plan your pruning strategy.

Leveling the Playing Field

Here’s an exercise to get you thinking about how you place yourself within the natural environment: Focus on a tree in view, and then close your eyes. Try to think of that tree as just as important as yourself, your house, your automobile, your cable access, etc. ...

Hard to imagine? You’re not alone! Most of us are so used to harnessing the environment for our own service, it’s hard to imagine this relationship being any different.

- Hardware Hotline January, 2003

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