There is a running debate in the green industry about pruning; how much to prune, what time of the year to prune, is pruning good or bad for plants, should plants be pruned at all? Recommendations for pruning have changed considerably over the years. Thanks to some great research, techniques have been modified in favor of the tree and the upshot is “less is more.” There are actually standards developed by ANSI (American National Standards Institute) referred to as the “ANSI 300” that detail proper pruning practices for tree care professional, and while they are not “laws,” they provide a framework for the industry to follow.
You will poorly prune and make mistakes pruning, but not to worry, because it is how we learn and usually a poorly pruned plant will go unnoticed. In the tiny world of your yard, it is best to try to keep the pruning to a minimum by limiting it to mostly what is dead, diseased, dying, touching, or “just plain” in the way. Dead limbs are usually the ones with no leaves, so they should be pretty easy to spot. The diseased branches usually have some outward sign like fungi, plant tumors, or oozing sap. Dying branches could be broken and hanging there, cracked, or split. Touching branches can actually damage each other every time the wind blows, so remedying that situation is a positive for the plant.
There are exceptions though to this minimalist approach to pruning. Sometimes a shrub is simply too large and it requires pruning by half. There are also plants that only have leaves on the top and need a bit of rejuvenation. There can be branches that hang so low you hit your head on them every time you mow the lawn, or flowering plants that need to be “dead-headed,” or taking off the dead flowers after they're done blooming. Most plants are very forgiving of anything you can do to it, so get in there and get the job done.
There are some general rules to try to follow:
Pruning is easy to do; you can buy yourself some tools at the local garden center or hardware store and have at it. But, if you want to prune well and in accordance with the ANSI 300, you will need to get some literature and learn something about it. A good starting point is always the local agricultural cooperative extension office. There are brochures, booklets, and fact sheets developed by the local state agricultural universities that are very informative. Rutgers, the State University of New Jersey has a list of publications with very helpful information as does the University of Maryland. These two are the ones I have used the most over the years, but they are not exclusive by any means so explore the publication list from the university in your home state. These same sites may offer one-day classes in pruning and pruning techniques that may be useful, the fee is usually nominal and the information can be invaluable.
Through the process of learning the art and techniques of pruning, there are some common mistakes to try to avoid. Before the first cut is made decide what the goal should be: Is the goal to uncover a window, does room need to be made for other shrubs around it to grow, is the sidewalk blocked? The goal is to remove the part of the shrub that is the obstruction and leave the shrub with a balanced shape. Sometimes, removing a branch is sufficient and sometimes more will have to be removed, but decide ahead what you want the final shape to be and set out string lines or other markers, like tying strings on the shrub, to define the final product. These are some of the most common mistakes (that I may or may not have learned from personal experience...):
These publications explain the perfect world of pruning, but it really takes some practice to do this well and make good cuts. No one does it perfectly all of the time and it is common for real world situations to present you with mission impossible. The good news is that plants are very forgiving. But, if by chance you over-prune and the next season's leaves fail to appear, oops! I won't tell anyone if you don't.