You remember all those freshman college classes that ended in “101”. For some reason, I always felt less intimidated by the course if the title ended with that number. So welcome to Pruning 101, where we cover the pruning basics from A to Z.
While pruning can be intimidating for many people, it doesn’t have to be. In fact, once you know the pruning basics, you’ll quickly grow your confidence. Before you know it, you’ll be pruning like a pro.
Understanding pruning basics are an essential skill to a thriving garden and a more assertive gardener.
The First Thing to Know
Every gardener has heard that pruning is important. But getting out in the garden and doing it is a frightening challenge for many. After all, you’ve worked and waited so long to get those trees and shrubs to grow; and now you’re going to lop off some of that hard-earned plant growth?
It may seem counterintuitive, but the fact is this:
The very best way to stimulate a plant to grow is to cut it back. Sometimes WAY back.
Pruning is done for the following reasons:
- To control size and shape.
- To remove dead or diseased branches or limbs.
- To improve overall structure and health by allowing more light and air in.
- To encourage new growth or flowering.
Think of it as addition by subtraction and while that may not make much sense from a mathematical perspective, the science behind it will make you a believer once you see the results firsthand.
Why this Works
Inside a plant’s terminal buds and growing tips, a hormone called auxin is stored. Auxin’s job is to suppress the growth of other lateral buds below. Think of it as a traffic cop, holding back a line of cars. Only when the traffic cop is gone can those cars that have been waiting for race onto the freeway.
Remove a plant’s growing tip by pruning, and you also remove the auxin. The nearby plant buds are no longer suppressed and will grow rapidly in response to the auxin’s sudden absence. If leaf buds are present on both sides of the branch, you’ll likely get two or more new branches for each one that’s cut.
But make no mistake, once a limb is severed from the plant, there’s no going back.
Making that first cut can be intimidating—downright terrifying. So here are five steps to help you master the pruning basics from A to Z, taking you from a newbie who’s afraid of the blade to a ninja who wields the steel with utmost precision and skill.
1. Timing is everything
There’s a time for everything, and some seasons of the year are better for pruning than others. If your job is simply to remove dead or diseased branches, go for it whenever the mood strikes. Otherwise, factor in the following considerations:
Late winter/early spring: The best time to prune is just before new growth starting to develop. Although pruning does stimulate new growth, this doesn’t apply during dormancy. Most plants and trees utilize stored energy from fall and winter to produce new growth just below the pruning cut when conditions are favorable, starting in spring. That’s when temperatures and day length signal the appropriate time.
The exception is for trees known for heavy sap flow, like walnut, maple, birch, and chestnut. With these varieties, excessive sap can bleed out of a pruning wound and result in potential stem dieback. Wait to prune these trees until early summer, when the leaves will draw sap past the cut, reducing the chances of excess moisture at the wound.
Early spring is also a good time to provide established trees and shrubs with a top dressing of organic nutrients. Apply an organic fertilizer, like Milorganite, to the root zones. Demands will be high with new growth after pruning and putting nutrients back into the soil in time for the stresses of the new season and summer will pay big dividends to the sustainability and vigor of your shrubs and trees.
Early/mid-summer: The next best time to prune is after full leaf expansion. Be aware, though, that much of a plant’s stored energy is already gone, used to produce new spring growth. Cut this new growth off now, and it’s wasted. Yes, you will stimulate the plant to put out more new growth, but this extra demand can be stressful to the plant in the summer months when conditions are likely to be dry and hot, and the plant’s reserves are at a premium.
Early/mid-fall is the least favorable time to prune. Pruning now can encourage the plant to produce new growth just as it is sending nutrients and energy into reserves for the cold months to come. Re-routing those reserves can result in new growth that’s weak and more susceptible to damage or death by the colder temperatures. And that creates the perfect access point for over-wintering pests and diseases, especially for evergreens.
2. The rule of thumb for flowering shrubs.
Certain shrubs bloom on new wood, producing flowers on the current season’s growth.
Examples include abelia, clethra, and certain hydrangea varieties like Annabelle. These plants should be pruned in late winter. They will produce flowers the same year. (For a specific example when it comes to pruning butterflybush, check out this very popular article).
Other shrubs produce flowers on old growth (wood from the previous year). Azalea, rhododendron, holly, forsythia and some hydrangea varieties like oakleaf, and the classic mopheads (Hydrangea macrophylla0 are in this category.
Pruning these in late winter would remove all the new flower buds that were formed after last year’s flower display. Shrubs blooming on old wood should be pruned immediately after flowering and before new buds are set.
3. Have the right equipment.
Your pruning tools will be one of two main cutting styles: bypass or anvil.
- Bypass pruners use a blade that passes by a non-blade part in a cutting action similar to scissors. This type of pruner is best for live plant material when a clean cut is essential, and you don’t want to crush the remaining portion of the plant. Personally, I use my trusty bypass pruners for almost all of my pruning tasks.
- Anvil pruners use extra force to squeeze the branch or limb as a blade passes through the wood and stops against the other side of the tool. These are best for cutting dead limbs or when you’re not worried about crushing or damaging the remaining plant material.
4. Pick the place.
As in real estate, it’s all about location, location, location. If you cut too far away from the bud, that new growth you’re hoping for may never happen. Cut too closely to dormant leaf buds, and they may be damaged to the point that they won’t recover nor sprout at all.
For stems or branches with buds located in pairs (opposing one another on each side of the branch as seen in the top image in this post), make the cut straight across — with no angle — about a half-inch above the bud pair.
For branches with a single bud below your cut point, select a spot on the branch about a quarter- to a half-inch above an outward-facing bud. Then make the cut at an angle with the high point facing outward.
5. Know your limits.
How much is too much to prune? In general, a good guideline for live plant material is to limit cuts to no more than one-third. For branches you want to keep but shorten, measuring from the tip back, take no more than one-third of the total.
To be clear, this does not mean shearing off one-third all the way across the entire plant. While shearing is a technique used to shape plants in a formal landscape design, this discussion does not apply to that method whatsoever. Unlike shearing (also referred to as heading), my references to pruning are as a selective, thoughtful, methodic process, one branch at a time.
While some plants respond better than others to more severe pruning, your chances of overdoing it are greatly reduced if you stick to this one-third guideline. Remember, you can’t undo a cut.
Another reference to the one-third guideline pertains to plant renovation. Over the course of several years, many plants’ branches become less productive and excessively woody as they age. Hydrangea macrophylla (classic mophead) is a good example of that. Using the one-third guideline, you could identify the oldest, woodiest of the branches and cut no more than one-third of the total plant’s branches all the way back to the ground.
Doing so will remove the most unproductive wood while making room for new twig growth from the base. Over the course of three (or four years by removing only 1/4 of the plant’s branches to the base each year), you could rejuvenate the entire plant over that time.
And a final point. The information above was written as a guide to shrub pruning. While some of these principles will apply to tree branches, making the wrong assumptions can severely damage or even kill your tree over time. If you’d like to learn more about making the right cut when it comes to tree branches, start by reading my post on that first.
There is no need to fear pruning. Once you understand the pruning basics from A to Z, you can see how and why in most cases, pruning is advantageous to the plant. Then it’s simply a matter of getting started (always the hardest part). The more you do it, the more confidence you’ll have about it. And before you know it, you’ll be pruning like a pro.