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A tree may need pruning for a variety of reasons:
· to remove diseased or storm-damaged branches
· to thin the crown to permit new growth and better air circulation
· to reduce the height of a tree
· to remove obstructing lower branches
· to shape a tree for design purposes
Once the decision has been made to prune, your next decision is whether or not to tackle the job yourself. In the case of a large tree where you want to remove big branches in the upper area of the crown, it may be best to hire experts. Large tree pruning, in particular, can require climbing and heavy saws or even cherry-pickers and chain saws. However, there are new tools available that can make this a manageable job. (Click here for more.)
Whether the tree is large or small, the key is to prune the unwanted branch while protecting the stem or trunk wood of the tree. Tree branches grow from stems at nodes and pruning always takes place on the branch side of a stem-branch node. Branches and stems are separated by a lip of tissue called a stem collar which grows out from the stem at the base of the branch. All pruning cuts should be made on the branch side of this stem collar. This protects the stem and the other branches that might be growing from it. It also allows the tree to heal more effectively after the prune. To prevent tearing of the bark and stem wood, particularly in the case of larger branches, use the following procedure:
1. Make a small wedge shaped cut on the underside of the branch just on the branch side of the stem collar. This will break the bark at that point and prevent a tear from running along the bark and stem tissue.
2. Somewhat farther along the branch, starting at the top of the branch, cut all the way through the branch leaving a stub end.
3. Finally, make a third cut parallel to and just on the branch side of the of the stem collar to reduce the length of the stub as much as possible.
A similar procedure is used in pruning one of two branches (or one large branch and a stem) joined together in a 'u' or 'v' crotch. This is known as a drop crotch cut. Make the first notch cut on the underside of the branch you're pruning well up from the crotch. For the second cut, cut completely through the branch from inside the crotch well up from the ridge of bark joining the two branches. Finally, to shorten the remaining stub, make the third cut just to one side of the branch bark ridge and roughly parallel to it.
Trees naturally close wounds that result from branch removal, so ideally, pruning wounds should be left to close without any help from you. Also, since most pruning should be done in late fall or winter, insects should not be much of an issue. However, there exist some circumstances when it is preferable to seal the wound with a non-asphalt-based pruning sealer such as Tanglefoot Latex Pruning Sealer. In particular, you should seal pruning wounds on trees that are susceptible to damaging insect infestation such as birch, oak, and elm trees. Also, if the weather is particularly dry, a pruning sealer will help the tree retain more moisture.
For most trees, the dormant season, late fall or winter, is the best time to prune although dead branches can and should be removed at any time. Pruning during the dormant period minimizes sap loss and subsequent stress to the tree. It also minimizes the risk of fungus infection or insect infestation as both fungi and insects are likely to be in dormancy at the same time as the tree. Finally, in the case of deciduous trees, pruning when the leaves are off will give you a better idea of how your pruning will affect the shape of the tree. Some fruiting and flowering trees should be pruned at other times of the year, depending on whether they flower on the previous year's growth or not. After pruning, it is always a good idea to give the tree a good fertilizing so that the tree can naturally close the pruning wounds and to reduce the stress placed on the tree. The TreeHelp Annual Care Kit is an excellent fertilizer program to boost the overall health of the tree after pruning.
When deciding how much to prune a tree, as little as possible is often the best rule of thumb. All prunes place stress on a tree and increase its vulnerability to disease and insects.Never prune more than 25% of the crown and ensure that living branches compose at least 2/3 of the height of the tree. Pruning more risks fatally damaging your tree. In some cases, storm damage, height reduction to avoid crowding utility lines or even raising the crown to meet municipal bylaws, your pruning choices are made for you. But even in these instances, prune as little as you can get away with.
Advice regarding tools is pretty straight-forward. Buy the best tools you can afford and keep them in good condition. There are also some new pruning tools out on the market that you may not have heard of that can greatly decrease the effort involved in pruning.
Images adapted from USDA Forest ServiceAfter each tree you prune, remember to disinfect your pruning tools in a solution of 1 part bleach to 9 parts water followed by cleaning with soapy water and then drying. Tree diseases are easily spread by infected tools. Finally, if you're not skilled in the use of tools like chain saws or if the pruning job is more than you're capable of managing, hire an expert. Safety first.