One of the most important aspects of tree and shrub management is knowing how and when to prune - done correctly the specimen will be not only aesthetically pleasing but healthy.  Pruning is not difficult once you understand the basics of how, why and when to prune.  

There are several reasons why gardeners should prune trees and shrubs.  Pruning should be done to promote health and growth by removing dead or dying branches injured by disease, insect infestation, storms or other damage.  Branches that are rubbing together will eventually create an opportunity for disease so one of the two should be removed.  Disinfect tools between cuts if disease is present or suspected.

The development of a strong framework in deciduous trees through proper thinning and formative training will help prevent disease and loss of vigour while maintaining the natural form of the tree.  Ideally a tree should be pruned to allow a few strong limbs well spaced apart up and down the trunk.  Pruning begins with the young tree and continues over a period of time as the tree gets larger.  Evergreen trees rarely need pruning as they tend to develop a strong structure naturally.  

Pruning can also be done to rejuvenate older trees and shrubs.  In trees, pruning part of the crown increases air circulation and reduces the leaf area that the root system supports.  The remaining branches will grow more vigorously enhancing the health and appearance of the tree.  Larger branches need to be pruned using a three-step cut method  to reduce the weight of the branch.  The first cut is done from underneath at about 30 cm from the trunk.  This is to prevent the branch from breaking off and tearing the bark.  The second cut is done a little further out on the branch from the first cut until the branch breaks away.  The third cut is done just outside the branch collar.  

Pruning is also done to maintain the intended purpose in the landscape:  encouraging flower and fruit development; maintaining a dense form for a privacy hedge; maintaining a desired shape; improving bark or foliage colour for winter interest in some species (e.g. dogwoods, heather).  Size can be managed if needed but ideally trees and shrubs are selected with existing space in mind.    

Plant appearance can be improved through judicious pruning.  For most landscapes, the plant’s natural form is often the most desired.  Pruning can be done to control the plant size as may be the case with both shrubs and trees.  Light pruning will keep evergreens well-proportioned and looking good.  Branches and undesirable fruiting structures that detract from the overall appearance of the plant can be removed. 

Pruning for safety - to protect people and property - should also be done.  This means removing dead branches, pruning out narrow-angled tree branches that overhang homes and walkways or anywhere that a falling limb might cause injury or property damage.  Hazardous trees may have to be taken down by a qualified tree removal service.  Crown lifting may need to be done for trees near walkways and roads.  This entails removing lower branches for the clearance required

Pruning for special effects such as topiary, bonsai and espalier can also be done with specific pruning techniques.

The appropriate pruning tools should be used for the job at hand.  Hand secateurs can be used to prune young trees and most shrubs.  Loppers are a good choice for somewhat larger tree branches and a pruning saw - either manual or motorized - is best for large branches greater than eight centimeters in diameter.  Be sure to use the right tool for the size of branch:  if the branch does not fit nicely into the jaws of the tool, it is time to move up to the next.  Tools need to be rust free and sharp.  If disease is present tools must be disinfected after each cut.