Pruning shade trees
When pruning trees, be sure to use the proper tools, and be sure that they are all in good condition. Hand pruners are useful for branches less than one-half an inch thick. Limb loppers should be used for branches one to one-and-one-half inches in diameter. For limbs up to 30 feet high, use pole pruners. Hand saws are the most common tool for homeowner pruning, but take extreme care when pruning with a power chain saw. Avoid power tools not specifically designed for pruning. Consider professional help for pruning larger trees.
To remove a large branch, make an undercut on the branch about one foot from the trunk. The undercut should be just deep enough to cut the bark of the tree, along the bottom quarter of the branch. This cut prevents the bark from tearing down the trunk when the branch is cut.
Then, on the top side of the branch, two inches further from the trunk than the undercut, cut all the way through the branch.
Cut the remaining stub of the branch just slightly outside of the bark ridge. The ridge is the area of the tree where the branch slopes away from the trunk. Leaving the ridge on the tree is vital for the tree to heal.
Never remove more than one-third of a tree canopy during one season. Dead and dying wood can always be removed, but do not prune too much of the live wood.
Most trees can be pruned at any time of the year. Some exceptions are American elms and crabapples which should be pruned in the winter to abate disease spread. Aspen, silver maples, birch and walnut trees exude sap if pruned in the later winter or early spring; but this will not harm the tree.
For more information, see the following Colorado State Extension fact sheet(s).
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Updated Friday, April 19, 2013