A plum tree needs to be pruned for it to stay healthy and produce quality fruit. Prune your plum tree annually for the first few years to encourage good fruit production and establish the ideal framework, which is usually a pyramid or standard shape. Pruning after that time will rid the tree of disease and dead wood. Knowing how much to prune is important, since too much can negatively affect the health and appearance of your plum tree.
TIP: Our expert gardening advisor, Rachel Klein adds, "Every time you prune, remove dead, diseased, or dying material first, no matter of the location. Cut loose any damaged pieces that may be stuck in the tree."
The Ideal Time to Prune
Prune your plum tree in June—the growing season—when the chances of healing are quicker and contracting silver leaf disease are minimal. This fungal disease, once contracted, spreads through the entire tree, greatly reducing the size, quality and quantity of your fruit. It enters the tree through cuts so incorrect pruning can be life threatening for a plum tree.
Prune on a dry day. Pruning in cold winter or damp weather increases the plant's chances of contracting disease. Never prune plums in the winter.
TIP: Rachel advises, "Avoid midsummer pruning or you may find your plum is putting all its energy to beautiful new growth instead of fruiting."
You will need to use a very sharp pair of clean pruning shears. A dull pair will crush the wood, which can invite infection. Make cuts as clean and small as possible. After pruning your tree each time wipe your shears with a cloth soaked in bleach. This will kill off any harmful bacteria or diseases and keep your trees healthy.
You may want to seal bigger cuts and wounds with a protective sealant to prevent silver leaf disease from entering the tissue. Protective pruning sealant is available from garden supply stores or can be ordered online.
The First Year
Remove dead leaves and branches as well as anything that looks sick and is stuck. Cut the main branch of your tree no more than 3 feet above the soil for a bush, 2 feet if you want a pyramid shaped tree and 6 feet for a standard shaped tree. You should make your cut just above a bud. Then, remove that bud. Make sure there are at least 3 buds still underneath the cut. You can remove a branch to ensure the remaining branches have adequate room and grow and receive good sunlight.
TIP: Rachel recommends, "Remove branches that intersect or that rub up against each other. Make all of your cuts at a 30 degree angle."
The Second Year
Prune again in June of the second year, cutting the main trunk just above the budding branch. Below this cut there should be at least 3 branches. Trim the remaining year-old branches just above healthy new buds, cutting to about 10 inches. Once again, make clean cuts at a 30 degree angle, avoiding jagged ones.
The Third Year
For the standard shape, do not cut the main trunk when you begin to prune in June of the third year. Instead, cut the stems from the main trunk until they are about 12 inches long, and cut back any stems growing off these to about 6 inches.
For the pyramid shape, cut the main trunk again to the first healthy bud, and cut back any new branch grown this year to 10 inches.
A Mature Tree
After the third year, just cut off any dying or dead branches and dispose of them properly. The best way to do this is to burn them to avoid the spread of silver oak disease.
Remember to keep an eye on your tree to avoid unnecessary overcrowding of branches. If they need it, cut them in June. The branches needs adequate sunshine to bear healthy plums and should not have to fight for it. Also cut back any new growth that fails to yield fruit, ensuring a healthy crop the next year. Trim all side shoots to 6 leaves from their parent branch to further encourage fruiting.