Winter to early spring is the season to trim these fruits: apple, cherry, elderberry, grape, nut trees, peach, pear and plum.
Blueberry trees should be trimmed in the winter.
Summer is the time to prune these fruits: apple (the only fruit that needs two annual trimmings), blackberry, crabapple, raspberry and wild cherry.
The citrus tree can be pruned any time, except for hot weather. Olive trees should not be pruned when it's too cold (below 20 degrees F) or the sap is running.
Late winter to early spring is generally the time to prune trees because: The wounds will heal quickly when growth begins; there are no leaves to get in the way of trimming cleanly; the bark is less likely to tear; and the wounds won't be further damaged by subzero weather. Pruning shouldn't start until trees have been fully dormant for several weeks, and must end before buds swell and when temperatures don't drop below 40 degrees F.
To avoid hurting younger trees, start pruning with the oldest trees.