Plum trees must be pruned differently than other trees to avoid the possibility of spreading silver leaf disease, a fungal infection that causes leaves and branches to turn a sickly brown or purple. Silver leaf disease can kill a plum tree. While most fruit trees should be pruned in the winter or early spring before they show signs of new growth, plums need to be pruned in June, at the height of their growing period, so they can fight off fungal infections such as silver leaf. Sharpen all cutting tools so that branches are cut and never crushed during pruning.
Cut out all dead or diseased wood. Burn or dispose of the wood away from your plum tree. Soak your cutting tools in a bleach and water solution (9 parts water to 1 part bleach) between cuts to avoid spreading disease.
Prune all branches that grow sideways across the tree's canopy. Cut any branches that rub against each other, as this can provide an entry point for infection.
Decide on a shape for your tree and plan your final pruning cuts based on that form.
Cut the tips of branches as far back as old wood (last year's growth) if necessary to achieve the desired shape for your tree. Make all cuts 1/4 inch from the outside of leaf nodes.
Top your plum tree within the first three years by cutting 2 to 3 feet off the top of the main trunk, cutting back to 1/4 inch above a branching bud. This will encourage root development, a thicker crown and additional fruit.
Paint all cuts with a tree sealer or with a latex paint to discourage insects from entering the tree through the cuts.