Thanks for writing in to ask about pruning your Italian plum. Like most fruit trees, plums benefit most from pruning around February, before the buds have started to break. When you go to prune later this winter, there are some ground rules to keep in mind, and also some strategies that might help guide you as you are deciding what to cut.

First, some pruning basics to remember:

Pruning Budget - You can remove up to a third of the canopy of the tree. This is based on the leaf cover in summer, so you will have to use your imagination somewhat to envision this.

Dead Wood - Remove all dead branches. These do not count towards the above pruning budget.

Diseased/Delinquent Branches - Remove any crossing branches that are rubbing another branch. Also take out any that are diseased or sustained damage from the previous year. You mentioned that your tree has many thin branches - this is one way to decide which ones to remove.

One you have removed the worst of the crossing branches and any dead, damaged, or diseased wood, you are ready to start pruning to support fruit production. Here are a few things to keep in mind:

Thinning Cuts - You want to maintain light and airflow through the branches, and allow sun to penetrate to the fruit. This can mean significantly thinning out the branches, as you suggested. There is no hard and fast rule about which branches you choose to keep or remove, but you might try to think about how easy it will be to pick the fruit, how much sun will hit the fruit, and which direction the branches are growing. Remove any branches that are pointing back inward towards the center of the tree, or that will make harvesting difficult.

Heading Cuts - Think about the weight of future fruit on the branches. If a branch seems thin and weak, consider cutting it back to the 3rd or 4th bud above the start of last year's growth, to prevent branches from breaking due to heavy fruit set. Choose an outward facing bud to cut back to - this will encourage outward growth in the next year.

There are lots of great resources online about fruit tree pruning that you might find useful. This guide from OSU Extension includes some good diagrams, descriptions of pruning strategies for both new and mature trees, and a video of how to thin a crabapple (the basics of this are comparable to your plum).

I also really love Cass Turnbull's Guide to Pruning, written by the founder of the Seattle-based non-profit Plant Amnesty. It is easy to read, funny, and full of helpful drawings.

I hope this information is helpful to you. Best of luck with your tree this coming year!

Sarah Bronstein

Master Gardener '22