If you have a heavily overgrown tree, spread the pruning process over a period of three years. Removing too many branches at once will result in an unproductive tangle of suckers and water sprouts. Follow the rule of thumb that you can remove a third of the live wood each year.
First, cut out and burn all dead, damaged, diseased, and insect-infected branches. Then gradually thin the healthy wood, removing all vertical growth-like water sprouts, branches that grow toward the center of the tree, and branches with weak, narrow crotch angles (less than 35%). Encourage horizontal branches, since they are the most fruitful, and prune more heavily in the top of the tree so that sunlight reaches the lower limbs.
Source: Rodale's Book Of Hints, Tips, and Everyday Wisdom
By one.of.a.kind from AL
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Productive fruit trees with an abundance of high quality fruit don't just happen. They result from good cultural practices, including pruning. Pruning is often neglected either due to a lack of pruning skills and knowledge or a fear that one is going to injure or kill the tree.
This is a page about pruning cherry trees. Pruning your fruit trees is important for their health and fruit production.