Good pruning of purple or purple-leaf plum trees helps keep them in good condition, well shaped and producing fruit. It also helps the tree avoid disease, especially silver leaf disease and scales, which is easily spread when branches are too close together, dying or diseased. Choose the right time of year and the right method to help your purple plum trees thrive and grow to their full potential.
Time the pruning of purple plum trees properly. Unlike many other trees, you shouldn't prune in winter, because silver leaf disease can take hold more easily. Prune in June, when new growth is strong but the tree still has the summer to recover and put on more growth. Scales are another common problem of purple plums, for which the best remedy is the sunlight and air that is let in by pruning.
Prune for shape and health. Cut away any dead, dying or diseased wood and remove one of any two branches that cross, as they will compete with each other. When pruning for shape on older trees, be sure you are only taking off new growth that will not bear fruit that year. For good plum production, restrict new shoots to six per parent branch. If your purple-leaf plum has an existing case of scales, don't be afraid to prune heavily to let in plenty of light and air.
Cut as cleanly as you can. Use sharp shears for small twigs and branches, and a sharp pruning saw for larger branches. Avoid crushing the wood as much as possible.
Seal larger cuts with protective sealer, available at landscaping and garden stores. This will help large cuts heal better and more smoothly. Follow any directions on the manufacturer's label for timing and amount of sealer used, but generally you will need a small paintbrush to work the sealer into the cut.
Dispose of any diseased wood by burning, not by composting. You can compost simple dead or unwanted branches, but any that show signs of silver leaf or scales should be burnt to avoid the spread of disease.