Answer: Pruning is one of the most satisfying of garden jobs. Unfortunately many gardeners avoid this task because they are not sure WHEN to prune certain trees. I'll start with a few general guidelines.
In general, it's safe to prune during the inactive or dormant period, ideally late winter to early spring, as long as the trees are not frozen. It's usually not a good idea to prune in late summer or early fall because pruning stimulates growth and the new tender shoots may be damaged in the upcoming colder months.
However for every general rule there are exceptions, and maple is one of them. While it is not harmful to the tree to prune in late winter, maples are "bleeders" (the sap flows freely). All cuts during this time will "bleed." This is not harmful to the tree, but could create an untidy situation. Under such circumstances maples and other bleeders can be pruned in midsummer when the sap will not run.
Pines are also specific in their pruning needs. Except for removing any dead branches, most pines require little pruning. But some pruning can be beneficial to produce a denser tree. New growth on pines at the tips of the branches is called a "candle." Pruning should be restricted to cutting new growth of the candles back about halfway. This is done after the candles elongate but before the needles expand in spring. While this is difficult to describe, once you observe the tree in spring, it will become clear.
Flowering cherry and pear are also exceptions to the general rule! Spring flowering trees are pruned immediately AFTER bloom which would be late spring or early summer. The reason is that the flower buds are formed on last season's growth and to remove it in late winter would cause the loss of the flowers for that year.
If you are uncomfortable with tackling a pruning job, just start slowly, doing a little bit. With time you will gain confidence, and your trees will be more attractive and healthier for it!
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