Mature plum trees require light pruning to maintain health and ample fruit production. Plums are prone to silver leaf disease, which attacks the tree through open cuts caused by pruning or broken limbs. Due to this problem, prune mature plum trees in June during dry weather to reduce chances of infection. Avoid pruning in winter or early spring and make sure the tools are sharp to reduce damage to the tree when cutting branches. It is a good idea to use a disinfectant on the tools between trees when pruning more than one tree.
Look for dead or diseased branches and cut these off completely.
Trim about one-third off the end of new growth to promote strengthening of the lower branch.
Assess the centre and lower branches to make sure they are getting adequate sun and air circulation. Cut back higher limbs that are casting too much shade, and remove newer growth in the interior of the tree that is reducing air circulation.
Look for branches that are growing across each other and cut one off, as they are likely to rub against each other on windy days and become damaged.
Apply pruning paint to any cuts over 2 inches if desired, to reduce the likelihood of disease.
Limit pruning on mature trees to new growth if possible, which will not bear fruit until the next year.