Pruning is a very useful garden maintenance practice that is best done proactively before troubles arise. Not all woody plants will require it but it should be part of a gardener’s routine maintenance for many reasons.

As a topic, pruning is very complex. This article will cover the basics and give you some ideas. For more advanced pruning issues or specialty techniques, check the resources listed at the end of this article.

Before You Start – are you sure you want to do this?

Pruning trees and shrubs at the wrong time can do more harm than good. Removing stems and branches opens up a plant to air and light but also to disease opportunity in the open wound and pests that attack while immunity is compromised. Pruning a flowering shrub at the wrong time can also remove all blooms for that year.

Most mature plants won’t respond well to severe pruning. Shaping a plant gradually is best. If a tree or shrub is vastly oversized for the space it’s in, consider moving it rather than pruning.

Since plants get food & energy from their leaves interacting with sunshine, severe cutbacks cause sudden catastrophic loss of photosynthesis that will harm and possibly kill a tree or shrub.

So, before you start, make sure pruning is necessary, is the right choice for that plant, and it’s the right timing.

Why We Prune

Many people are nervous about pruning correctly. Some wonder if it’s even necessary. Others just worry about doing it wrong and harming the plant.

This article will review how to ensure we are cutting the right branches, in the right way, and at the right time. I also caution all gardeners to understand the reality of mature plant sizes. Instead of fighting Mother Nature, we should be realistic about the natural size and shape of our landscape plantings. If it’s the wrong plant in the wrong place, pruning is not the right solution.

Here are five basic reasons for pruning:

1. To remove property and safety hazards
2. For maintenance of the health of the tree or shrub
3. Training a young specimen
4. Aesthetics – flowers, foliage, shape, restrict growth, correct uglies or reversions
5. Fruit production

What to Prune

The top priority is to prune the 3 D’s – Damaged, Diseased, Dead branches or stems. Leaving damaged or diseased wood is like leaving an open wound – it can allow further spread of disease or allow a pathogen to settle into the wound and thrive. It’s wise to remove the damage with a clean cut.

Pruning for Health (Your’s and the tree’s):

• Remove property or safety hazards such as dead or dying overhead branches, esp those next to housing and property lines or any branches interfering with power lines.
• Rectify structural issues and future points of failure due to winds, ice, or snow load. Examples include double leaders (co-dominant or competing leaders), overweight unbalanced canopy, and narrow v-shaped crotch angles where bark and branch form a weak spot and entry point for decay. Also, look for and prune out crossed branches with rubbing points where pests and disease can gain entry in the future.
• Plan long-term health for a young tree or what will become a large shrub, by creating a strong structure referred to as scaffold and selecting appropriate branches for long-term development. Read More here about Pruning Young Trees.

Pruning for aesthetics (primarily for our own purposes, not for plant health)

• Improve the quality of flowers, foliage and stems by pruning out twiggy weak growth or discoloured branches and deadheading old blooms.
• Restrict growth when a plant is slightly blocking a path or a window or to shape it to block a bad view. Keep in mind that if a significant amount of pruning is needed annually, you’ve likely got the wrong plant in the wrong place. If it’s still a younger tree or shrub, considering moving it to where it can naturally develop to its mature size.
• Rejuvenate an overgrown woody shrub either by removing suckers, thinning it out, or even cutting it right back to the trunk base, This works well for some specific shrubs. I’ve had success with cutting back rose of sharons, weigela, and forsythia to a few inches from the ground and they have bounced back well. Many shrubs won’t tolerate such severe treatment though, so do a bit of research before you start hacking away.

Pruning for Fruit Production – This is advanced pruning that requires very specific instructions depending on the type of fruit tree. See the specialty pruning references at the end of this article.

When to Prune

NOT at the time of planting. Let it settle and establish. It’s an old myth to cut back a newly planted, or transplanted shrub. That plant needs energy to reestablish itself and it gets that from the photosynthesis of its leaves interacting with the sun. So, leave the leaves and branches alone as much as possible when you move a woody plant.

The type of plant affects when best to prune

ALERT – Oak wilt fungal disease is affecting oak trees. Symptoms include leaf discoloration, wilt, defoliation, and death. The fungus spreads from diseased to healthy trees from pruning tools, insects, or by root connections with infected trees. Red oaks and Pin Oaks are particularly susceptible. Help prevent infection by avoiding pruning from April through August.

• Evergreen Conifer Shrubs – pinch tips in winter.
• Evergreen Broadleaf Shrubs – early spring.
• Deciduous Shrubs – generally, prune right after they bloom.
• Evergreen Conifer Trees – typically don’t prune at all.
• Deciduous  Trees – prune after they lose foliage in Fall.
• ‘Bleeders’ (trees with sap) – prune mid-winter before sap starts running.

Dormant Season is best for many woody plants as no diseases or insects are active and it’s easier to see any structural issues on trees (leaders, narrow crotches, crosses) after the leaves have fallen.

Spring is okay for some summer-flowering shrubs – but not great for trees.

Early to Mid Summer is best for spring-flowering shrubs. Many diseases and insects are active at this time and the open pruning wounds will attract them. However, this is the time to deadhead and reshape spring-flowering shrubs right after they finish blooming. This timing will produce optimal flowering next spring.

Late Summer / Early Fall – Don’t. Why not wait until the growing season has ended? Dormancy is the safest time. If you prune late in the summer, new growth may not have time to harden off for winter and you’ll suffer some die-back.

Rule of Thumb for Evergreens -Leave evergreen conifers alone except for some very mild pinching unless you know what you’re doing. Most are unforgiving and won’t fill in if you’ve cut back to their brown stems. Two notable exceptions are yews and cedars which can handle a good trim in the spring. Tip – a good pruning practice for pines is called ‘candling’ to help control size and increase bushiness. Do this in June.

Pruning practices:

Cut just above buds, not too close, and don’t leave a stub.

Big heavy branches require a special method called a ‘3-point-cut’. If you try using just one cut, a heavy branch will break and tear as you’re cutting, peeling excess bark, and leaving a bigger damaged area more susceptible to insects and disease.

Keep in mind the symmetry of branching so the tree maintains good shape and balance as it grows.

Rejuvenate some twiggy plants and cane-based plants that produce side growth or suckers by cutting some or all of it to the ground. This is effective for removing excess bulk from lilac or for starting over with an overgrown weigela.

Common Mistakes

• Don’t prune at the time of planting or transplanting. Let the plant settle and establish itself.
• Avoid snipping away at the outer edges of woody shrubs year after year or you’ll end up with twiggy outer growth. It is more beneficial to make a few large cuts back at the trunk or main supporting branch.
• If you shear everything into formal shapes, you’ll likely remove most flowers, and will weaken the plant over the years. This method works for boxwood but for most other shrubs you’ll be attempting to totally defy the natural shape of the plant. If your desired look is formal and you have a yard full of forsythias, bottlebrush, viburnums etc,  you will never be happy and neither will your shrubs. Learn to live with their beauty or replace them.
• Topping! Never top a tree or have an “arborist” do so. Lopping off the top of mature trees encourages wispy weak growth and ruins the tree structure forever. The BAD about Tree topping 
• Cut only to the branch collar of a tree, NOT flush to the trunk. That’s the best place to allow the tree to heal well.
• Avoid girdling the bark with any cuts, ties, or decorations. Once girdled, the path for energy to reach the treetop is severed, and that’s game over.
• Never use pruning paint to patch a new or old pruning cut. That’s an old myth and has been proven to be worse than allowing the plant to heal itself!

Tools – Use the right tool for the right job.

• Pruning shears or hedge clippers for light stems that aren’t too woody for example a lavender plant or spiraea.
• Secateurs or bypass pruners for the small woody stems up to approximately 2 cms (1/2 inch),
• Loppers for reaching further and getting branches up to 3 cms (1 inch).
• Pruning saw for anything more than 3 cms (1 inch).
• Chain saw for anything you can’t cut with a pruning saw.
• All should be sharp and clean. And by the way, bleach is NOT recommended to disinfect tools!

Create a Pruning Plan

I recommend that gardeners don’t wait until a plant has outgrown its space or become a troubled, diseased specimen before deciding to prune (esp evergreens as they don’t respond well at all to heavy pruning). A bit of proactive pruning for shape and some touch-up pruning to remove the 3 D’s is likely all you need.

Consider what woody plants you have in your garden and make a plan for which month to prune. You’ll be protecting your investment and making your life easier by planning and solving any issues when they’re small rather than later …hopefully not after a branch has fallen on your roof or your neighbour’s!

Here’s a brief Pruning Primer Video to enjoy!

PS. Specialty pruning for Fruit trees

• Fruit trees – to control the size of the tree, distribution of branches, promote fruit production and help control crop load. OMAFRA – Pruning Fruit Trees 
• Pruning apples – video – University of Maine extension service
• Espalier – is often used for fruit trees by pruning and tying branches to a frame so that they grow flat against a structure such as a wall, fence, or trellis. Here’s a how-to article  
• Pruning Overgrown Apple Trees – The Garden Professors

Resources for general Pruning

One of the best resources – Clemson College – Principles and Practices for Pruning Trees

• Fine Gardening has some good links about Pruning
• Purdue University Pruning Guide
• How to Prune Trees – an excellent resource from the USDA Forest Svc