Why prune trees? There should always be a specific measurable goal in mind before a tree is pruned. Trees never need to be pruned ‘just because’. Grass is mowed and hedges may be trimmed, but trees require no routine pruning. Pruning seldom improves the health of a tree although in some cases described below, pruning could benefit the tree. Trees are overwhelmingly pruned to accommodate human desires.
The following are common reasons to prune trees:
Clearing limbs from buildings, especially roofs and chimneys. This is probably the most commonly encountered reason to prune live, healthy growth from mature trees. The goal is to clear buildings by about 10 feet, while pruning as few large limbs as possible in accomplishing that. The larger the cut, and the closer to the main trunk, the more likely disease will enter through the wound and begin a cycle of decay.
Storm damage – trees damaged by storms do not necessarily need to be removed, but removing or shortening damaged limbs and pruning broken stubs to better future branching points will benefit the tree.
Removing dead wood – There is no harm in leaving dead limbs on a tree in most cases, as far as a tree is concerned, but large dead limbs should be removed if they pose a hazard to people or property below. Limbs of large trees look much smaller than they really are. A good arborist can help you decide if dead limbs are a hazard or not. Dead wood on smaller trees can be removed for aesthetic reasons. A favorite but tired old cedar might be made to look like a feature tree again by removing the dead wood and a bit of creative pruning here and there.
Retrenchment pruning – this is a specialized type of pruning performed on old trees that have been declining in the top of the canopy but are showing strong growth lower down. The tree is pruned back to the vigorous growth points.
Raising of the canopy for access, such as lawn mowing. This is another common pruning request. Again, the goal is to make yard work and access easier for you, but limit harm to the tree. Limbing up a tree drastically is usually a bad practice.. The more large cuts are made at the trunk of the tree the more likely damage and disease will take hold. Sometimes a compromise is the best solution. Often limbs can be made lighter by selective pruning at the tips without having to cut right at the trunk.
Pruning to improve a view or to allow more light in a garden. This kind of pruning is difficult to accomplish in a way that minimizes damage to the tree while resulting in a vastly improved view, or resulting in significantly more light to the garden.
Crown reduction. This is another type of pruning that is often requested because of interference with buildings or other infrastructure. There is an acceptable but limited way to accomplish this in some cases, especially on younger trees or shrub-like trees, but in many cases it cannot be done without seriously harming the tree. Many people ask for a tree to be reduced for safety reasons, but again, such drastic pruning, often accomplished by ‘topping’ the tree is an unacceptable practice in modern arboriculture that almost always results in the decline of the tree and often can result in decreased instability rather than increased stability which was the original goal. Topping trees seriously reduces their value and negatively impacts your property value.
Formative structural pruning of young trees. This pruning, if required is done on young trees within a few years of planting. The goal is to space crowded limbs, remove crossing and rubbing limbs and correct competing leaders.
Ornamental pruning of Japanese maples and other small architecturally significant trees. This involves detailed pruning featuring many small cuts in order to showcase underlying architecture. Layering and ‘cloud pruning’ are two examples.