Winter is an ideal time to prune deciduous fruit and shade trees, since the trees are dormant and you can more easily see the tree canopy. In many cases, pruning can also help prevent or control certain insect and disease problems.
For help with pruning, visit the UC IPM web page called Pruning fruit and shade trees and shrubs.This page provides links to plant-specific pruning information for fruit trees, nut trees, landscape trees, and others. You can also find links to diseases and environmental disorders that commonly affect fruit and shade trees, as well as additional information on the topics of landscape management and videos on how to train young trees.
It's important to note that while pruning many types of fruit trees in winter is advised, you'll want to wait until summer to prune apricot and cherry trees. Read Avoid Pruning Apricots and Cherries in Cool Season to find out why.