To prune or not to prune

Topiary shrubs

The topiary garden at Hampton Court Palace, England. Photographed in February, 2015.

Pruning is one of those divisive words that can inspire fear, joy or annoyance but I think we can all agree that a shrub or tree, when in need of a trim and correctly pruned, looks the better and is healthier for it. But that’s the problem. How do you know what needs to be pruned?

BRIEF COMIC INTERLUDE: The photos at left and below were taken in February, 2015, at Hampton Court Palace where gardens, unlike those in Southern Ontario, generally tend not to be buried under a heaving crust of snow and ice in late winter. And, as this was home at one point to King Henry VIII, you can appreciate why the topiary is at the pinnacle of prune-liciousness. But….back to reality.

What to prune     Organic gardening methods tend to focus on working with the plant rather than forcing stuff upon them. When interfering with the natural growth of a plant, less really is more. Here are some thoughts to help you decide what to prune:


At commercial fruit farms, trees are pruned to allow more light and heat to the fruit within a tree’s canopy. This can stress the tree (see below). But agricultural practices focus on maximum yields not maximizing the tree’s lifespan. Trees on farms are regularly replaced when yields drop and pruning no longer improves fruit production. If you want to keep your fruit tree for beauty and shade, it’s gorgeous blossoms in spring time and a harvest of homegrown fruit for as long as possible, resist the urge to remove a lot of branches from the canopy as so many gardening advice columns recommend. Yes, you’ll get less fruit but how much fruit do you really need? Here’s a link to a good article on fruit tree pruning in Canada for more information.


I see lots of advice in various gardening media about pruning to allow light and air to reach the inner branches of a tree thus creating a healthier tree. When you study botany, you learn that the leaves inside a tree canopy and in the lower half of the canopy (essentially leaves that don’t get a lot of exposure to sunlight) have evolved to photosynthesize using the amount of sunlight they do get–which kind of makes sense. When you take out branches to “open up” the canopy science tells us that those smaller leaves within the canopy, upon being exposed to extra light for which they are not designed, suffer overexposure to UV light and heat stress.

Instead, look for dead or dying branches and, of course, branches that present a safety concern. Lots of gardening pros recommend that you also prune out diseased branches as well. But, unless the diseased branch is dying, consider keeping the branch. If you cut it off, you’re not removing the source of the disease which originally came from the air (as an airborne pathogen) or soil and the cut makes another entry point for the disease as well as stressing the plant.

If you have to cut off a branch, don’t use a wound dressing. There are a lot of products available that are sold as an aid to protect and heal a cut but research has shown that, in fact, these products tend to assist decay and prevent the wood from healing.


If you don’t prune a flowering shrub, it will eventually grow woody and you’ll get fewer and fewer flower buds. So whether you’re looking at a forsythia, an hydrangea or a bridalwreath spirea, a regular trim is actually a good thing. The general rule of thumb is to prune spring flowering shrubs immediately after they’ve flowered. Prune summer flowering shrubs in early spring before they’ve bloomed. Here’s a link to a comprehensive guide from the Colorado State University Master Gardener program that includes clear explanations about why you’re pruning and which shrubs need to be pruned when.



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