Pruning is among the most important aspects tree care and maintenance. It affects the longevity, health and the tree's ability to resist storm damage. Unfortunately, this maintenance procedure is often misunderstood because of the myths that cloud its true value.
Myth #1 Trees will grow just fine even without pruning. It is true that forest plants grow perfectly well with nature's own way of pruning. But the trees in most suburban yards have different needs. Most suburban trees require some form of pruning to keep and maintain their shape and to eliminate fast-growing water sprouts. When pruning a tree, keep in mind that you should never remove more than 1/3 of the crown in just one pruning.
Myth #2 Cutting too close to the trunk will help the tree to heal quickly. Trees don't actually heal, meaning they can't replace damaged or lost tissue. They can only cover their wounds by growing new layers of wood. When pruning, avoid pruning too close to the tree's parent limb and retain the branch collar.
Myth # 3 Pruning wounds that are more than three inches in diameter must be coated with wound dressing. Tree wound dressings or sealants are petroleum-based products that are traditionally used to seal freshly cut wood and prevent decay or insect infestation. However, studies show that using wound dressing, seals in moisture, causes decay, inhibits compartmentalization and eventually causes cracks that may expose the tree to pathogens. It also slows down the production of new layers of wood.
Myth # 4 Prune back the tree's crown to compensate for root loss during transplanting. It is not a good idea to prune trees after transplanting except when there is a need to remove dead or broken branches. The crown of younger trees should not be pruned back to make up for the lost roots. Minimal pruning is necessary during the first three years of planting the tree.
Myth #5 Pruning certain species of trees early in the spring will cause bleeding which may lead to stress and health problems. It is true that there certain trees like maples and birches that "bleed" from pruning cuts done early in the spring. However, this bleeding doesn't hurt or stress the trees. Bleeding often occurs when a tree loses its sap which is quite inconsequential in the general health of the tree. With some exceptions, you can prune trees anytime of the year. But the best time to do it is during the tree's dormancy or after the flowering period. The worst pruning time is when the tree has just leafed out during spring.
Resources: http://www.72tree.com/tree-service-atlanta.html http://ezinearticles.com/?5-Common-Myths-About-TreePruning&id=7541734