Why Do Trees Need to Be Pruned?

Trees that we plant in our yards and along streets interact with our homes, our utility connections, local wildlife, and even us! Since trees in neighborhoods and urban locations are more isolated than those in nature, they need our help to keep them in good condition, good health, and safe from the dangers of the built environment. In this article, we’ll go over some of the main benefits, techniques, and best practices to help your Nashville trees thrive.

Pruning and Trimming Trees

When a tree is pruned, branches are cut to promote growth in a certain direction, to favor a certain shape, or to prioritize healthy branches over others. Trimming, on the other hand, is done to remove unhealthy, dead, or unwanted growth. Both have the effect of thinning out a tree to allow better airflow and more sunlight into interior branches. When we prune or trim a tree, it must be done intentionally; otherwise, it could result in damage to the tree (as in the case of tree topping, when whole limbs are cut back to stumps on the trunk, which is a misguided practice that can easily kill a tree).

Good tree pruning habits are important because healthy trees stay around longer, providing ecosystem services like air filtration, creating shade, and contributing natural beauty to an area. Big, mature trees perform these services best while also adding value to your property. Maintaining trees in healthy condition over the years by removing dead material and keeping them in good shape will support them throughout long, productive lives as part of the local ecosystem.

When to Prune Trees

Tree pruning is an ongoing requirement for trees from the time of planting and throughout their decades of maturity. Caring for the tree’s development over its lifetime significantly helps a specimen stay in the best condition that it can be to produce ecosystem services and remain safe near buildings, power lines, vehicles, and people. 

Trees should be pruned:

• Every year or two as a sapling matures

• Every five to ten years for mature trees (with visual assessments every year or two by an arborist, if possible)

• When sick or dead branches are visible (missing leaves or broken and hanging pieces)

• When inner branches are overgrown (removing overgrowth for wind to pass through branches helps the tree stay stable in storms and allows more light into the inner crown)

In terms of the best time of year to prune a tree, winter is generally the best, while minor pruning can be taken care of in any season if there’s a pressing issue. 

When to Contact an Arborist

Simple pruning and trimming of a tree can be done by almost any adult, but caution should be exercised when using tree-trimming tools like saws and shears. Professionals have experience making cuts of all sizes on trees of all heights, so while homeowners may be able to handle young and small trees under ten feet, professionals should be called to work on larger trees. 

We asked our resident master arborist, Michael Davie (board-certified master arborist with Bartlett Tree Experts), when residents can prune their own trees and when they should think about calling an arborist: “People can prune trees themselves if the trees are small enough and the cut parts aren’t large enough to cause damage or injure someone if things went wrong.” Certified arborists are trained to use specialized tools for pruning and trimming trees, and while homeowners can use some of the smaller devices for smaller cuts, large equipment should be left to be handled by a professional.

Tools of the Trade

Tree care professionals have a range of tools at their disposal for small, medium, and large cutting projects. The smaller ones can be purchased by homeowners to keep in the garage for simple home maintenance, like small branch removal or leaf trimming. 

• Safety equipment – Safety gloves, eye protection, and hard hats keep even small jobs free from scratches or cuts. Professional arborists use harnesses and roping equipment to get up high in trees and safely lower large cuttings.

• Proper clothing – Long sleeves, long pants, and boots provide further protection during jobs where someone may rub up against trees or experience branches falling.

• Arborist pruning saw – With a long, thin blade and a short handle, a pruning saw is used for small to medium cuts.

• Folding saw – Another small pruning saw, this one folds up and can be easily carried around from tree to tree.

• Pruning shears – Pruning shears are used to trim small to medium branches. There are two main kinds: anvil shears, which have one blade that moves and cuts into a stationary blade, and bypass pruning shears, where one blade makes a deep cut across the second one. Loppers are large, two-handed pruning shears.

• Pole pruner – Pole tools have a long reach with a rope pulley system that controls the saw or shears. They are specialized forestry tools that should only be operated by a trained professional since they are used for high-up cuts that result in overhead falling material.

• Chainsaw – Chainsaws are motor-operated cutting tools that certified professionals use for cutting large branches and tree trunks.

• Lubricant for shears – A lightweight household lubricating oil keeps shears in their best working order for strong, smooth, and clean cuts.

• Pruning sealant – Michael Davie shared with us that “pruning sealant is not needed, and studies have shown that it can even be detrimental at times. The only time it may be useful is on pruning wounds in summer in areas with diseases like oak wilt (which we don’t have here) or Dutch elm disease (which is rare here).”

The Basics of Tree Pruning

When a tree is being sized up to prune, certain best practices should be kept in mind, whether by a professional or homeowner:

• Assess the tree. Identify what species it is and what its healthiest shape is, and look for damaged or dead branches and competing central branches like the central trunk or major lateral branches.

• The smaller the cut, the healthier it is for the tree. This is why doing this over the tree’s lifetime is important: to train it in the healthiest shape and condition and remove problems early for minimal maintenance later.

• Only prune what’s necessary. The fewer cuts, the better!

• Don’t remove more than 10-20% of a tree’s canopy at once. Fewer leaves mean less photosynthesis and less energy to the tree.

• Mind the branch collar. Don’t cut a branch too close to the trunk; more on this next!

What Is a Branch Collar?

A branch collar is found at the base of a branch where that branch grows off of the main trunk or limb. This juncture where the tree and branch diverge needs to be extra strong to support the weight of the branch, and the collar is full of specialized tissue that supports the healing process if a branch breaks off. If a pruning cut is made too close along the trunk, effectively removing the collar, that tissue is unable to create a healthy seal at the cut, which may then remain open and exposed to infection by disease or pests. 

How to Prune Correctly

When deciding whether to contact a professional arborist or do the work yourself, consider your knowledge and experience, the size of the project, and the intended outcome. Small cuts may be able to be done by you, but big pruning projects should be left to a professional for the best results. As Michael Davie says on the matter, “The value of the trees to you (the homeowner) may be relevant in the decision; there is more possibility of making mistakes or causing some problems with DIY work. But if you have a good set of bypass-style hand pruners or loppers and a sharp Japanese-style handsaw, there’s a bit you can do.” 

When taking small pruning and trimming jobs into your own hands, remember the reasons to prune:

• To encourage a strong form of the tree (strong central trunk, strong lateral limbs)

• To remove dead and dying branches

• To remove crossing and rubbing branches

• Interior cleanup for the tree’s canopy to have good sun exposure and ventilation

Different types of cuts include:

• Pruning cuts to stimulate growth of remaining leaves and/or branches

• Thinning cuts to remove small branches from larger branches 

• Heading cuts to cut branches only partially to encourage new buds and shoots, increasing internal growth (the opposite effect of thinning cuts)

A particular cutting method that is good to use when removing medium to large branches is the three-cut method. This cutting method protects the tree collar while preventing ripping when the branch is removed, significantly reducing the impact to the tree when cutting. The first cut is an undercut a third of the way into the branch, one to two feet out from the trunk. The second cut is a top cut into the branch from above, an inch or two out from the first cut, which removes the outer bulk of the branch. The final cut is outside of the branch collar to remove the remaining one to two feet of branch from the tree. 

Here’s a useful diagram that shows of the three-cut method of pruning.

Common Mistakes to Avoid

Tree pruning is careful business, and sometimes, what not to do is just as important as what to do. Here are a few practices to avoid:

• Ripping branches from the trunk – This damages the tree collar and the bark at the connection, leaving the rip open to potential infection and improper healing.

• Lion’s tailing – This happens when too many internal leaves are removed from a branch, leaving only the ends with leaves, looking like a lion’s tail. This can hamper photosynthesis and just doesn’t look good.

• Over-thinning – Removing too many leaves and branches reduces the tree’s ability to photosynthesize and, like lion-tailing, leaves a tree looking thin and empty.

• Cutting important main branches – While trees do grow new branches, it takes a long time, and important main branches may contribute to a tree’s health due to the amount of leaves they contain or by providing structure to the tree as a whole.

• Tree topping – Cutting large branches and limbs down to stumps along the trunk of a tree will create a lot of stress on a tree by opening up a wound and removing a significant amount of leaves and woody material from the tree. This leaves the tree open to infection, with a lower capacity to create energy and heal.

• Pruning and trimming a tree yourself when you should call an arborist – Large projects should be left to professionals to be sure everything is done right and safely. When in doubt, ask an arborist! They can also guide you on how to do home tree maintenance between arborist appointments. 

Benefits of Pruning Trees

From improved air quality and cooler local temperatures to added curb appeal and increased property value, maintaining trees in healthy condition with regular pruning enables them to create the many benefits that mature trees produce where they stand. Not only does pruning trees keep them healthy; it makes them safer! Healthy trees are less likely to break in wind or storms, and trees that are regularly thinned allow wind to pass through rather than being caught by a too-full crown like a sail. 

If you’re thinking about replacing a tree or planting a new one, remember to keep it properly pruned as it grows! Browse our selection of trees available through our annual tree sale (open from October through February) to support Nashville’s local tree trade. And to help us get more trees on the ground, volunteer with us! For more tips on tree care, as well as information on Nashville tree news, sign up for our newsletter.