[header] How to prune plum trees [title] Prune at the right time. [step] You can prune the tree while it is dormant in winter or in summer. Dormant pruning is pruning the tree during the late winter, when no new growth is happening and the tree doesn't have any leaves. 
Pruning while the tree is dormant encourages vibrant growth come spring, and it's less likely to cause damage to the tree than summer pruning. Summer pruning can be used to slow the growth of a tree that is getting too big and to thin new growth that is overcrowding.