Pruning 101

Robert Glendinning of Agriculture Canada shows where to make a cut, at the branch bark collar, using a small handsaw. Note that he isn’t actually pruning this drooping pear tree in the Arboretum – if he does prune it, he’ll do it in late winter or in the summer. PHOTO: J. HUMPHRIES

By Jennifer Humphries

Taking care of your urban tree starts with the basics – watering as needed, caution when mowing around the trunk and exposed roots and, for a seedling or sapling, keeping it staked until it is ready to stand tall on its own.

But sometimes more is required. You see a stray branch or a dead one, a split or tendency to grow in a direction you didn’t intend. Before you pick up your tools, please read on, and then follow up with a handy guidebook (Canadian or North American), an authoritative article from a government, university or college website, or a talk with a gardener or arborist you trust. Pruning can help your tree but, if improperly done, it can do serious damage.

My starting point to prepare “Pruning 101” was a conversation with Robert Glendinning to tap his expertise on trees. Glendinning has worked with Agriculture and Agri-Food Canada in the Arboretum for 15 years. As stated by the Friends of the Farm, “While he finds himself involved in everything from pruning to tree removal to data management, his passion is the propagation of trees and shrubs. The result is evident in the nursery and in the Arboretum’s new plants, essential to renewing their ever-changing tree inventory.”


You may prune for shape or aesthetics, to remove lower branches to create a canopy tree, or to remove a diseased or dead branch. Sometimes your tree is congested or bushy, and you want to let the air circulate to prevent disease and to allow the lower branches to get sunlight.

A key reason to prune is to avoid having branches touch and potentially damage your home or a power or cable line. Hydro Ottawa frequently prunes around power lines – sometimes not as judiciously and lightly as homeowners would wish. If it’s possible for you to take care of possible problems before Hydro Ottawa sends in their trimmers, you may be able to ward off the heavy pruning. Unfortunately, if you have a tree on city property with a power line near it, Hydro Ottawa’s guidelines are likely to leave your tree with the infamous V-shape or C-shape – it will still be viable, though certainly weaker. Web search on “Hydro Ottawa” tree trimming for their guidelines.


Glendinning advises that there are two optimal windows for pruning. One is late winter, when the tree is still dormant. Another – which he finds to be the best time in the Arboretum – is July and August.

The worst possible time to prune is the fall because, in effect, you are putting wounds on a tree that won’t have time to heal before the freeze. Another poor time to prune is the spring during or just after flowering, or sending out leaves: the tree has just used up all its strength to leaf and flower, and pruning at that point stresses it at its most vulnerable.

An internet search can offer you pruning time recommendations by tree type or species, but the advice above is simple, easy to remember and, generally, will serve you well.

According to an article from goodhousekeeping. com “Why You Should Stop Pruning Your Garden in the Fall”, ‘…Absolutely, do not prune if it’s wet out, it spreads a lot of diseases,’ explains horticulturist April Johnson, landscape coordinator at the Rodale Institute. Damp weather encourages the growth of microbes that will make the most of the damage your pruning does. ‘Wait until the sun’s out for a little while; it dries out and kills mold and bacteria, she says.”


Glendinning offers two key pieces of advice:

  1. Prune at the branch bark collar. This is the connection between the trunk and the branch. Don’t cut into the collar. What you want to have is a cut at the connection point where there are cells that are well equipped to heal. Eventually, if correctly done, a circle of healthy callus will swell around the cut. A good resource is Garden Notes #613 Pruning Cuts from Colorado State University Extension: csfs/pdfs/613.pdf
  2. Use the appropriate tool. Ideally use a bypass pruner. It makes a better cut than an anvil pruner which tends to crush soft plant tissue. If you use a bypass pruner, which works like scissors, you do almost no damage to the tree. If you’re pruning a larger branch, you may need to use a handsaw, a small pruning saw that cuts both ways. Whatever pruning tool you use, make sure it is clean before and after use. This is particularly important if you are pruning due to disease, but it’s best to be sure they’re clean in all cases. Either a small amount of bleach diluted in water or a spray of rubbing alcohol will do the trick. Soapy water will kill most germs. For quality tools, take a look at Lee Valley Tools or Ritchie Feed and Seed.


Primary reasons to call in a professional are personal safety and the safety of property. If the pruning is at a considerable height or the branch in question is of substantial girth, an arborist is best equipped to do the job. Concern for your own well-being is a key determining factor in calling a pro. Another is that, in urban neighbourhoods such as the Glebe, your neighbour’s home is as likely as your own to be affected by amateur branch removal gone awry.

When calling a professional, Glendinning advises that you choose an arborist certified by the International Society of Arboriculture (the Ontario Chapter is at www.isaontario. com). It’s also a good idea to ask neighbours and friends for recommendations based on their experience. Most arborists are as keen on tree preservation as their removal, but some are more attuned to the techniques needed to maintain a healthy tree.

RESOURCES For pruning techniques with diagrams, see Agriculture Canada’s web article – search on Agriculture Canada Pruning – link

For fruit trees, see:

Jennifer Humphries is co-chair of the Glebe Community Association’s Environment Committee. You can contact her at environment@

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