Why Prune Trees? Reasons You May Choose to Prune

Trees can grow quite happily on their own — they’ve been doing it for hundreds of millions of years — but sometimes, it may be necessary to do a little maintenance when trees and people are living in close proximity.

Why prune trees? I’ll do my best to explain the variety of reasons below.

Reasons to Prune a Tree

The general advice from arborists is not to prune a tree unless you need to. Each cut you make or branch that you remove will affect the shape and growth of the tree. For example, experts agree that pruned trees will always be smaller than those same types of tree that haven’t been pruned, with some horticulturists referring to pruning as a dwarfing process.

As trees have evolved to make the most of their natural form and growth patterns, it’s often best not to interfere. However, trees haven’t evolved to live near our houses, in our yards and gardens, or along our roads. They also haven’t evolved to give us as much fruit as we might like!

Pruning for Safety

Tree branches that have died or that are broken or damaged, perhaps from a storm, can pose a hazard to adjacent structures and passers-by. Sometimes it may be necessary to remove a dead branch or one that’s hanging precariously to prevent it falling and hurting someone, to stop it falling onto a nearby roof, or to stop it dropping onto power lines.

Responsible tree ownership always involves making sure that the trees on your property or in your care are safe, both for their well-being and for the health and safety of anyone else around.

Pruning a tree for safety or in any sort of emergency is the only pruning that can be done at any time of the year. However, please bear in mind that, like with all types of pruning, it might be better for the tree and safer for you to request the help of a professional, especially if you need to remove a large branch or the tree is near buildings or electricity cables.

Saving a Tree

If a tree has been badly damaged by a storm or high winds, there are times when careful and professional pruning could save its life. In this case, it would absolutely be wise to contact an arborist for help and specialist advice.

Pruning Fruit Trees

Professionals and amateur gardeners alike often prune fruit trees. This can help to train the trees into a specific shape, for example when apple and pear trees as trained as cordons. Pruning fruit trees can also, when the pruning is done correctly, allow larger harvests of fruit.

Apple tree espaliered against a wall
Photo by Andrew Martin at Pixabay

Different methods of pruning can produce different results. It’s possible to encourage new fruiting shoots to grow in older fruit trees through selective pruning techniques. Other methods can remove the hormone-producing buds which may inhibit shoot growth, and prompt growth at various points below the cut.

Pruning fruit trees, like pruning any trees, can also introduce more light and air circulation into the branches. This, when done properly, can encourage additional growth, flowering, and fruit production.

Training a Tree or Managing its Size

Pruning a tree is not something to be taken lightly. While it is perfectly possible to prune a tree purely for aesthetic purposes, maybe because you’d like it to be a specific shape, or you’re not keen on the angle of a particular branch, it’s important to remember that a tree is living thing.

A tree is the shape it is, just like we’re the shapes that we are. Think carefully before you start cutting branches if there’s no concrete reason to do so, and remember that every cut is a wound that the tree will have to seal off. A possible exception to this is pruning for topiary, but as that’s done regularly and only involves trimming relatively new growth, it doesn’t have the same impact as pruning mature branches. 

Topiary Yew Tree
Photo by David Mark at Pixabay

Even if you are happy to leave a tree to its natural growth, there are times when its shape might cause problems. There might be a branch overhanging a roof or garage, reaching towards power or telephone lines, or obscuring a window or even a door. A tree could grow faster, taller, or spread wider than you expected, and so you may have no choice but to nudge its growth in a particular direction or remove some extra height / width.

It’s also possible that a tree’s branches might need to be removed to provide clearance. This could be to allow cables to pass underneath upper branches as often happens with telephone or electricity cables and trees planted at roadsides. It could also be to allow pedestrians to walk under the tree, or cars to pass beneath it.

In these cases, a few, sensitive cuts and a careful shaping of the tree can make life easier and safer for everyone. Again, it’s always best to consult a professional or do some research to determine exactly the best way to prune the type of tree in question.

But Never Topping

It’s a fairly complex subject, but I feel the need at least to mention here that arborists in general are strongly against the practice of “topping” trees. This is often seen in street trees. According to Virginia Tech, “Topping occurs when the vertical stem (leader) and upper primary limbs (scaffold branches) on mature trees are cut back to stubs at uniform height.”

Experts from across the world agree that topping is dangerous, destructive, causes more harm than it saves in the long run, and (least importantly) makes trees ugly! Don’t plant trees that will grow too tall for their locations, and if you find yourself with such a tree, consult an arborist to determine the best solution.

Pruning for the Undergrowth

Some trees have such dense foliage and canopies that little or no light gets through to the ground underneath. If there are other plants growing around the roots of the trees or the tree is planted in a lawn, careful pruning can help to open up the canopy without causing the tree too much damage. This will allow sunlight, water, and freely circulating air to reach ground level, sustaining grass, flowers, or small shrubs that may be growing there.

Increasing Light

In the same way that dense canopies can block light from reaching the ground, they can also stop it reaching windows. If there’s a tree planted in front of your home, and its branches and foliage are blocking out the light, correct pruning by an expert can help to let the sun shine in without hurting the tree too much.

Reducing the Potential for Wind Damage

While trees can provide very effective windbreaks, they can also be subject to damage from wind themselves. This, in turn, can damage buildings, cars, and even people if wind-broken branches crash to the ground or the tree uproots. The right pruning techniques can reduce a tree’s wind resistance, making it less susceptible to damage in storms and high winds.

Uprooted tree toppled by windy weather
Photo by ykaiavu at Pixabay

Improving Structure

Trees generally know how to grow on their own. But occasionally, whether due to genetics, overcrowding from other trees, an incident when the tree was younger, or the direction of light or wind when the tree was growing, a tree can develop with an unhealthy and / or unstable structure.

Qualified arborists know how to manage the shapes of trees to give them the best chance at stability and healthy growth with even weight distribution and balanced branch structures.

When to Prune a Tree

As mentioned above, emergency pruning — cuts done to remove dangerous branches or repair damage that could threaten the tree’s life — is the only type of pruning that can be done at any time of the year.

While every tree has different requirements, there are some general rules. Pruning is normally best done during late autumn or during the winter, although for some trees, the recommendations are a little different (see below).

The autumn / winter months will be the tree’s dormant period, and during this time, it will be less susceptible to stress. It will be better able to cope with the wounds pruning causes, and as pests and fungal diseases are generally less active during the winter months, there will be less risk of the tree becoming infected.

Gardener using secateurs to prune a tree
Photo by MireXa at Pixabay

In that same vein, it’s very important to be aware if the tree is infected with, or in an area prone to, any specific infections. The oak wilt fungus, a fatal disease in oak trees spread either by a sap beetle or by root grafts created by oak trees living in close proximity to each other (50 feet or less), is easily spread by pruning.

Pruning or cutting oak trees during the time their sap is rising will attract sap beetles to the wound. If the beetles are carrying the oak wilt fungus, the disease will be introduced to the tree through the wound. (If you absolutely must prune an oak in an area prone to oak wilt fungus during transmission times, experts advise sealing the wound immediately with water-based paint or shellac. Tree pruning sealant is not recommended.)

Risk of infection aside, it really is important, especially with certain types of tree, to respect the dormant period. I once cut one small branch off an acer (Japanese maple, in my case) during what I thought was still its dormant period: late winter just before spring really began. Unbeknownst to me, the tree had already awoken for spring; it began to “bleed” sap and wouldn’t stop for nearly 24 hours. I was panicking!

Thankfully, the tree did heal, and is still healthy today. (I’ve never pruned it since, as I later learned that most trees, acers included, are thought to be best left alone for the healthiest growth.) While it’s generally accepted that such wounds will heal over time, in rare cases they can be fatal, and the loss of too much sap can weaken the tree or shrub, making it more susceptible to disease.

Certain trees have a significant rise of sap in late winter and during the spring and are especially prone to bleeding; some so much so that it’s advised to prune them during the summer. It’s even more important to prune at the correct times for these trees, but always do a bit of research to find the optimum pruning times for any type of tree. And of course, bear in mind that optimum pruning times will depend on your climate.

Red-colored maple leaf
Photo by Ilyona Ilyés at Pixabay

Trees Prone to Bleeding

These are the trees that are particularly sensitive to bleeding. I won’t give you specific recommendations here, because climates vary so wildly from region to region. However, these are the trees that require extra care and precision.

  1. Acers (maples)
  2. Birch (It’s suggested by some horticulturists that birch trees shouldn’t be pruned at all as they can bleed so much, but there are better times and worse times if you have to prune them.)
  3. Hornbeam
  4. Walnut
  5. Pecan and Hickory
  6. Laburnum
  7. Magnolia
  8. Mulberry
  9. Poplar
  10. Sophora
  11. Tilia (also known as Lime, but not the citrus kind)
  12. Grape Vine

It’s important to note that, even with trees that are prone to bleeding, the use of tree wound or tree pruning sealant is almost never recommended.

How to Prune a Tree

The first thing to do is to research your particular type of tree and learn the best way to prune it to optimize its health. If you’re confronted with a dangerous or emergency situation, or the pruning work looks to be extensive, it’s always better to consult a professional, qualified arborist than to attempt something yourself.

If your tree only needs a few small trimmings, perhaps the removal of a few small, dead or broken twigs or branches, then it may be possible to carry out the work yourself. There’s a big difference between a little work to open up the dense crown of a small garden tree and removing a storm-cracked branch from an ancient oak!

Pruning Shears
Photo by Michael Schwarzenberger at Pixabay

If you do decide to prune your own trees, always make sure that you’re safe before you start anything. Protective goggle are useful, as are thick gloves and even a helmet if you’re working with larger branches.

Always use clean, sharp tools when you prune a tree, and make sure you’re using the right tool for the job. Don’t try to use small shears or secateurs to cut larger branches; you’ll traumatize the tree and risk hurting yourself too! Disinfect tools before and after each use to avoid the potential spread of disease from tree to tree. Clean up any pruned material off the ground quickly, and dispose of it safely.

There are plenty of books and credible internet resources out there to tell you exactly how and when to prune, and of course, your local arborist will always give you advice. Good luck, be careful, and enjoy your trees.

Featured Image by Gordon Lamont at Pixabay

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