Stanley plum trees that are properly pruned produce fruit much earlier in their lives, and live longer. Prune annually to remove deadwood and thin out living branches to allow air and light to filter through the canopy and reach all parts of the tree. A well-cared-for Stanley plum tree produces fruit at age 10, and continue until about age 20, if you prune deadwood annually and thin its branches every four to five years.
Put on gloves to prevent blisters, and safety glasses to protect your eyes from falling debris. Wear a hard hat if you will be pruning high branches that are more than 3 inches in diameter.
Look at the trunk of the tree, from the bottom up. Prune away any branches less than 2 feet from the ground on a younger tree, less than 3 feet on a mature tree.
Move higher and determine which branches you will cut before you start; aim to leave the tree with laterally growing branches spaced 8 to 10 inches apart.
Cut the central leader (the branch that forms the top of the tree) if it is more than 3 feet longer than the laterally growing, or "scaffold," branches. Cut with a pole-handled pruning saw if the tree is more than 7 feet tall.
Thin areas in the tree's centre with the pruning shears, cutting branching growth from scaffold branches if they are growing too thickly for light to penetrate the canopy. More light means more fruit. Prune dead and diseased limbs annually to increase light and ventilation, and to prevent diseases from taking hold.
Always wash tools and equipment after use to prevent transmitting diseases or insects to other trees or plants.
Never climb a tree to prune it, and always wear a hard hat and safety glasses when working on a mature tree.