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Pruning Trees- Introduction, Rules, & Tools:
Because trees are generally more costly and take longer to become established than other landscape plants, they deserve to be treated as an investment in your property. Watering to ensure adequate root zone moisture for two years after transplanting is probably the most critical factor of survival. But pruning during this time is the best way to create a safe and sound structure for future growth of the tree.
Generally, you can safely prune 10% to 15% of the canopy to improve its structure, but do not prune more than 30% of the canopy at any one time. To do so may open the crown so much that sunscald and temperature stresses will occur.
If you are unsure whether to remove a branch, then wait. You can always come back later to re-appraise its condition or status and decide whether to remove the branch. If you cut it off too soon, you cannot glue it back on.
Rules (these change as we get smarter):
An old rule was to “prune the top to match the roots”, because roots were destroyed when the tree was harvested, and the branches also should be eliminated to reduce water stress. However, this old rule is not true.
The root system is reduced when digging trees and transplanted trees will need adequate water in the root zone.
But new roots must be initiated and develop for the tree to establish successfully, and leaves of trees produce the food (carbohydrates) that will nourish new root growth. So, the best treatment for young trees is to prune properly for strength and structure (Gilman, 2002), but allow many stems and leaves to remain for nourishment.
Another old rule was to “apply pruning paint to the wound”, based on the thought that the exposed tissues needed protection from the environment. However, this old rule is not true.
Pruning paints contain chemicals that kill the tissue (meristematic cells) that will grow to seal the wound. Often the paint will crack and allow water to collect behind the sealant and rot the trunk tissue. If a thick layer of sealant is applied, it may act as a cover to protect insects that will nest in the wound cavity. The best treatment is to leave the wound uncovered. For cosmetic purposes, a compound called lac balsam may be applied to make the wound look less obvious.
Branches have a natural reaction zone at the junction of the trunk called the branch collar.
The tissue outside the branch collar is separate from the trunk itself. If you prune a branch and protect the branch collar, the wound area will be as small as possible.
Protecting the Branch Collar: Video Vignette (See it live!)
Pruning Rule of Thumb (to recognize branch collars)
Hold your hand out in front of you. Put your four fingers together and spread out your thumb.
Now pretend your doctor said you had to lose your thumb and you had two choices for removal: 1) you could cut it at the knuckle near your palm, or 2) you could cut it in line with your index finger to the wrist (think of the size of that wound!). Chances are you would choose to cut it at the thumb knuckle (we would!).
In this example, a cut at the thumb knuckle would represent a natural target prune to protect the branch collar. A cut along the finger line to the wrist would represent the old rule, a flush cut. It is not too difficult to see the difference in the wounds that would occur.
You won’t have these pictures along with you when you are pruning branches, but you should have your hands. Look at them frequently to remember our “rule of thumb” for pruning branches.
Tools: Basic Pruning Tools
Hand pruners are available in different sizes. Select one that fits comfortably in your hand. All hand pruners have a size limit, generally one-half inch, of branches they will cut. If you find yourself using two hands to squeeze the handles to make the cut, you are using the wrong tool and should select one of the following hand tools.
Typically, tree saws have slightly curved blades, but many of the modern short folding saws may have very sharp but straight blades.
Tree saws have one main peculiarity: PULL the blade to make the cuts and gently push the blade back to reposition it for another pulling cut. Trying to push the tree saw to make the cut will probably cause the blade to catch and bend, ruining it.
Professional arborists may use a ‘speed saw’ (bottom in picture) on the largest stems and limbs. Most homeowners will not need this large tool. Using the proper procedure, even the largest branches can be cut with tree saws. It will just take a bit more time and effort.
Pole Saws (bottom in picture above) are similar to pole pruners, but a saw blade is attached to the end. Some manufacturers make telescoping extension rods for poles, and other manufacturers use sectional extensions as shown with snapping locks. A pole may be extended to 24 feet if you are strong enough to manipulate it.
NOTE: arborists frequently use Chainsaws. For the purpose of this tutorial, we do not recommend the use of chainsaws due to their additional safety risks. If you have very large branches to prune, or so many limbs or trees to cut that a chainsaw may be required, we suggest you contact and hire a Certified Arborist. Or contact the ISA for their excellent instructional videos on chainsaw use and safety.
Purpose Right Tree / Right Place Selecting Trees Transplanting Trees Mulching & Staking Summary Diagram Pruning Trees Topping Hurts! Protecting Trees Tree Root Myths Pine Bark Beetles Live Christmas Trees Glossary List of Figures List of Video Vignettes Related Links Bibliography