We’ve compiled everything you need to know about pruning: the what’s, the why’s, the how’s and the when’s
If you’re someone who’s suffered from a quarantine haircut, you might know how a “quick trim” can end up being a disastrous mistake. We can apply this same understanding to pruning our trees, plants, and shrubs—without knowing what you’re doing, you may end up doing more harm than good.
So, to give you a leg up for the upcoming pruning season, we’ll share exactly what pruning is, why and how you should do it, and when the best time is to get out your shears and make some cuts.
What is Pruning?
If you’re unfamiliar with the science behind pruning , here’s a quick summary. The main growing shoot of a plant impacts the shoots located below. Pruning encourages growth of these other, lower shoots by impacting a specific hormone—auxin.
Auxin is released into the green tip of an actively growing shoot and is transported down the main stem to stimulate shoot growth. All of the shoot tips will compete for the hormone. When pruning takes place, the pathway that the auxin usually follows is interrupted. This means that dormant buds are able to grow into branches in an attempt to restore this pathway. This can be commonly seen as a proliferation in the conversion of lateral buds into branches, which takes place just below where the pruning cut was made.
With this brief look into plant hormones, it’s no wonder that pruning is normally met with some trepidation from gardners. It’s difficult to trim foliage, especially that which looks beautiful and healthy. It’s even more difficult to know what to cut when you’re inexperienced. Deciding what plants/trees to prune, where exactly to cut, and how much to be removed sometimes ends up being too burdensome to consider that we end up putting pruning off until next year.
So, let’s tackle that first question: what plants and trees should be pruned?
In addition to other related reasons for pruning (which we’ll discuss later), there are many perennials, trees, and shrubs that will grow stronger and produce more blooms if they’re regularly pruned. This includes woody plants and trees like roses, fruit trees, deciduous trees, hedges, and so much more.
Once you realize what needs pruning, you can begin to determine where and how to prune, which requires you to understand how the plant will respond to any pruning.
Understanding Shoot Growth
The shoots include the woody stems, as well as their appendages, leaves, and buds. Having some insight into the natural rules of shoot growth  will help you better understand where pruning is needed and how it will impact the plant as a whole.
Different plants and trees will have different patterns of shoot growth, and there are no specific pruning instructions that could be applied to all trees in all circumstances, but there are general rules that can be helpful with fruit trees and most deciduous trees:
- Two branches that emerge from the same location of the tree trunk and are identical in diameter and length will have the same growth potential. This means that they will receive similar levels of hormones and nutrients.
- If two branches that are identical in all respects (emerging from the same location, same length), the branch that’s thicker in diameter will grow more vigorously than the thinner one. Pruning the thicker branch may help to support the other one but, ultimately, if the limb becomes too large it may need to be removed entirely as it might prevent the development of other limbs around the tree.
- Given that all other conditions are the same, a branch at a steeper angle will grow more vigorously. As a pruner, check for any upright limbs (those that are growing at an angle of 30 degrees relative to the trunk) because these will grow too quickly and end up being unproductive. Conversely, any flat limbs that are growing at an angle of 90 degrees relative to the trunk (or more) will also be weak and any upright shoots that grow off of these limbs may end up becoming unproductive after a year or two (and only produce small fruit). That said, they should be removed so that healthier limbs can develop.
- With two branches that are growing at the same angle, the one that’s higher up will grow more vigorously than the branch that’s lower in the tree. This is important to consider because if there are two limbs that are of equal size, the one higher up will continue to grow more quickly relative to the lower branch and might end up shading out the lower limb(s). If it appears that there could be a problem in years to come, removing any large limbs at the top of the tree may be a proactive way to prevent problems.
- The dominant shoot in the center of the tree is referred to as the central leader. Branches that grow closer to this central leader will grow more vigorously than branches that are further away.
- Lightly pruned trees, or those not pruned at all, will flower and fruit at a younger age. Unless you notice a problem, like one of those listed above, that will restrict/prevent the growth of a branch, pruning a young tree should be avoided or only done modestly if you want to achieve early flowering/fruiting.
- Heavily pruned trees will generally result in smaller trees. A tree that remains unpruned will always end up with a larger trunk diameter than a pruned tree. Although severe pruning may produce more vigorous shoot growth near the pruning cuts, the overall growth will be reduced compared to a tree that is lightly pruned or not pruned at all.
- Later pruning (i.e. later in the spring) will result in shorter growth from the terminal bud. Pruning in the spring (after you already see some shoot growth) will reduce the terminal growth for the season—which can be a good thing for trees that have restricted fruiting because of vigorous growth.
Why People Might Decide to Prune
Beyond pruning to maintain and support the health of the tree or plant in question, there may be several other reasons you might decide to prune.
You may want to direct the growth of your plant towards a certain direction or to fill a specific space, like in the case of a formal hedge. Pruning could be purely for an aesthetic purpose, you might want to train the plant to grow to a specific size or shape.
Pruning may also be motivated by safety concerns. For instance, you may have a tree that’s approaching a power line, growing too close to the house, or is simply becoming too big. You also may have a fruit tree that is pruned to be lower to help make picking easier/safer.
Speaking of fruiting plants, pruning is an important component of ensuring quality fruit as it allows additional light to penetrate into the tree. The quality of the fruit or flowers will be directly impacted by the amount of wood on a tree or plant and reducing any unnecessary or unhealthy limbs will direct more energy to the growth of fruit and flowers.
What Tools Should Be Used for Pruning?
What tools you’ll use will generally depend on what tools you have available. While it may not seem that important, the quality of the tools will play a pretty big role in the quality of the pruned tree or plant. Try to purchase the best quality tools that you can afford.
Also, keeping these tools in a good condition is essential. Keep them well oiled and sharpened. Clean the tools regularly with denatured alcohol (which is especially important after pruning diseased wood).
- Hand shears (commonly called secateurs) – These can generally be used for branches up to ¾ inch in diameter.
- Lopping shears – These long-handled shears are better for branches that range from ¾ to 1½ inches in diameter.
- Pruning saw – A pruning saw is best for cutting branches that are larger than 1½ inches in diameter.
- Hedge shears – This is the best option for small shrubs, evergreens, or hedges, and can be used to cut branches that are up to 2¼ inches thick.
- Pole pruner – This is an essential tool for reaching dead wood or doing light pruning in trees (around eight feet or more). Pole pruners can cut through branches about 1¼ inches thick and both manual and electric options are available.
When Should You Prune?
Generally speaking, the dormant season (i.e. late winter, early spring) is the best time to prune any plants or trees that bloom in summer. This also the best time to tackle any major pruning, where a significant part of the tree or plant needs to be removed.
Why is the Dormant Season the Best?
When a plant is dormant, it goes through a phase where its metabolic activity is minimal or temporarily inactive. During this period, no new growth takes place and the plant conserves its energy until the weather changes again, the ground thaws, and new growth is supported.
When you prune towards the end of the dormant season, you’re setting up the plant or tree for success once it starts growing again. Pruning in late winter means that there’s less risk for disease or pests and the warming temperatures will help the new wounds on the tree or plant heal properly.
What if it looks like my tree is bleeding? After pruning, some plants will appear to bleed heavily. This may be quite alarming to witness but is generally not harmful. If you’re concerned about bleeding, you may want to wait a few additional weeks to prune as pruning that occurs after leaves have started growing (like in late spring) will minimize the amount of bleeding and allow the cuts to heal quicker.
If you need an even more specific recommendation as to when you should take care of pruning, experts suggest  that March is the most ideal month. This is because the risk of extremely low temperatures is rare and you can be more confident that any cuts won’t be subjected to winter injury—which is much more difficult to say in January or February.
In addition, the tree structure will be more apparent around March, so it should be easier for you to see the best places to make cuts. Similarly, because the buds and generally have not started swelling in March, they won’t be damaged by any falling limbs as a result of your pruning efforts.
Pruning throughout the spring and summer generally isn’t too problematic (may only result in fewer fruit or flowers), but you should avoid pruning after mid-August as this could subject new growth to winter damage.
How Often Should You Prune?
While most of us are guilty of the “I’ll just put it off until next season” excuse, it’s better to have smaller, more frequent (annual) pruning sessions than waiting for a severe pruning that only happens every couple of years or so.
Pruning Best Practices
- Remove branches that are broken, diseased, or appear weak, like those that form a sharp angle (around or less than 30 degrees) with the trunk.
- Avoid leaving stubs and try to cut as cleanly as possible. You’ll generally want to cut just above a bud, and do so on a slight angle.
- Remove any branches that appear to be growing in a downward direction, as they’ll continue to get weaker over time and will produce low-quality fruit.
- Look for branches at the top of the tree that are larger than those directly underneath them and prune them or remove them entirely to prevent shading lower branches.
- Remove all upright suckers or waterspouts. While fast-growing, these will generally never be productive.
- If a large amount of pruning is necessary (i.e. a fruit tree has overgrown the amount of space it’s been allotted), try to plan subsequent pruning sessions over the span of a two or three-year period. It’s generally a better idea to start with the lower limbs, because they’re weaker and pruning won’t stimulate rapid regrowth. Any attempts to minimize the height of the tree should be carefully planned because pruning in the tops of the trees may inadvertently stimulate vigorous growth.
- That said, pruning can be used to stimulate growth. If a tree has become weak (perhaps due to over cropping), more frequent/vigorous pruning may encourage vegetative growth.
- If a tree becomes so shaded that its production is impacted, reducing or pruning limbs at the tops of the trees may allow for improved light penetration.
- Regularly remove the root suckers (which are generally activated by damage caused by a weed trimmer or lawn mower) that are found growing at the base of the tree.
- Use heading pruning to remove the terminal part of a limb or shoot to invigorate thick and compact growth. This is a better pruning option for shrubs or fruit trees because it concentrates the energy of a branch and encourages more growth at that point in the following season.
- Use thinning pruning to remove an entire limb or shoot to maintain health, shorten limbs, or improve light penetration. This won’t generally invigorate growth and will help to maintain the natural form of a woody plant.
Final Thoughts on Pruning
While this is a good place to start your pruning planning, it shouldn’t be the end-all-be-all advice. Pruning is a complex subject and is dependent on many different factors. You should use this as a general guide but also take the time to study the specific characteristics of the plant or tree in question.
Having a good idea of a plant’s susceptibility to cold weather and its flowering date will help you determine the best pruning strategy for you. As always, we’re always here to help, too. Feel free to get in touch with any pruning or gardening questions you may have.