Why Prune a Tree?
Pruning the limbs of a tree promotes health, safety and beauty of the tree. Both dead and living branches can be a hazard when leaning over property and people, which is why high risk branches need to be pruned. Branches that interfere with signs, block portions of driveways and streets, as well as cross power lines should be pruned immediately.
Learning how to prune a tree is also detrimental to the overall tree health. Cutting in the right places can help shape the tree as well as induce better fruit growth. Many trees do a degree of self-pruning. When a branch does not produce enough “food” for the tree, it will likely die and fall off on its own. The exposed wound will callus over and heal itself. Loose branches can easily be blown to the ground in a windy event. When pruning trees correctly, humans are simply aiding in these natural processes. Pruning can help shape a tree into any desired form, either to avoid structures or to create a unique and interesting shape.
The act of pruning can remove parts of a tree which have become ridden with insects or rot. The crown of a tree can be thinned to generate greater airflow across the leaves. Crossed and knotted branches can be removed to create a stronger tree which can stand up to harsh weather.
Tree Pruning Terminology:
With young trees, the primary goal when pruning is to create structural strength. More emphasis on shape, health and aesthetic appearance will come as the tree grows bigger. Here are some terms you should know when learning how to prune trees:
Node: The part of a tree where one twig/branch connects to another. Cuts are always made at this point.
Internode: The piece of a branch between two nodes.
Bud: The point where a new branch will grow. Buds look like small green flower buds.
Crown: All of the branches and leaves that lie above the trunk.
Pruning Method 1 (Thinning the Crown):
Crown thinning removes up to 1/4 of the live branches at a single time. The purpose here is to thin the branches to allow more air and light to flow into the tree. Branches should only be removed at nodes, not at any U-points of strong connection. When two branches grow next to each other at a sharp angle, it forms a “U” shape. In between the two branches forms what it called “included bark” (a crack often forms here).
Thinning should be done evenly throughout the crown. Only cutting on the interior of the crown can create an effect known as “Lion Tailing”, where leaves only grow in a tuft on the end of a branch. This not only looks strange but creates additional weight on the ends of the branch. Thinning the crown evenly reduces the amount of “wind sail”, or how much resistance the crown has with the wind. Decreasing the wind stop reduces the chances of branches being broken off by wind gusts.
Pruning Method 2 (Raising the Crown):
Cutting and removing branches near the ground can result in the crown of the tree growing higher into the air. This creates more clearance on the underside for furniture, vehicles, people and signs. This practice is also used in the timber industry to prepare a tree for felling. Ordnances specific to each city require trees near public areas to be raised to a certain height. After trimming, the you should have 2/3 the height of the tree in crown and 1/3 in trunk. On young trees, you can leave weaker branches on the trunk to serve as “temporary branches”. These are left on to protect trees from the sun, but should be removed at some point in the future.
Pruning Method 3 (Reducing the Crown):
A tree’s natural inclination is to grow tall, so crown reduction should be only used as a last resort. When a crown grows too tall, such as into power lines, it must be reduced. Crown Reduction Pruning is the most popular method for doing this, as it creates a natural look, minimally stresses the tree, and lowers the time between prunings. This method creates the biggest wounds to a tree, and as such, can lead to rot and decay in the cut area. If a tree is outgrowing its bounds, it might be a good option to replace it with a smaller tree.
Executing the Cut:
The ideal prune cut removes only the branch and does not cut into the stem/trunk of the tree. Since the branch and stem tissues are separate, this cut results in a low likelihood for decay and better healing.
Live Branches: Start by looking for the branch collar at the base of the branch. The branch collar is a bulbous growth which supports the branch and sometimes has a small crack/seam at the top known as a branch bark ridge. When pruning, the branch collar must not be cut.
Make your cut very close to the branch collar at an angle which is perpendicular with the branch’s direction. If you cut too far away from the stem, you will leave a partial branch which will take much longer to heal. Cutting close to the stem allows the wound to heal as fast as possible.
Large branches: A three-step cutting method should be used on larger branches. 1) Make a shallow notch on the bottom of the branch several inches away from the branch collar. This stops the branch from tearing away tissue as it falls. 2) Follow the branch out an inch or two and make a cut completely through the branch, letting the limb fall. Finally, remove the remaining stub by making a cut close to the branch collar (near the trunk/stem).
Dead Branches: When a branch dies, the bark becomes hard and usually falls off. When this happens, you can easily see the line between the branch collar and the branch itself. This makes cutting easy- simply cut just outside of the bark collar, taking care not to cut into the tree. You can use the three-step method for large branches. The likelihood of tearing bark is reduced in this case because the wood is dry and dead.
Harming the Tree:
Two practices known as topping and tipping can serve to damage the tree’s health. In the case of topping, inexperienced pruners remove upright branches which sit between the nodes of a branch. With tipping, users cut lateral branches between nodes, neglecting to cut the branch close to the base.
Avoid these practices, as they can cause epicormic sprouts (weak, fragile sprouts which cannot support themselves), as well as the death of branches near the pruned branch. Bark ripping can be prevented by simply following the three step cutting method for large branches. Cuts into the flesh can create decay.