Answer: Basic pruning is done when it is needed rather than on a set annual schedule. Suckers from the roots and water sprouts or unnatural new top growth heading straight up should be removed as soon as you see them to avoid them taking vigor away from the productive crown branches. Any damaged branches should also be trimmed away neatly as soon as the damage occurs. Rubbing branches should also be removed before they can damage their neighbors.
Apple trees in a commercial situation are generally hard pruned every year to force them to produce the maximum crop of fruit. In a home orchard, you could conceivably prune in a more modified way and/or preserve a more ornamental character to the shape of the tree by following a less agressive or reduced pruning routine.
To some extent your pruning will be dictated by what has been done before, in the sense that some trees are trained to be open through the center while others have a central leader. Your county extension should be able to provide you with pruning instructions based on your particular tree and may even offer workshops on fruit tree pruning or care.
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