Prune the Aggressive Black Locust Tree
The black locust is an aggressive tree that requires a good amount of pruning. If not kept under control, the tree can cause problems. You can prune a black locust tree in any season.
When pruning the tree, don't take off more than 1/3 of the limbs at one time. Also, make sure you make cuts just outside the branch collar. Don't flush cut and don't leave any stubs behind. Proper pruning of this tree is important to ensure it stays healthy and doesn't sustain damage.
When to Prune
If you have recently planted a black locust tree, leave it alone for one or two seasons before pruning it for the first time. This allows the root system to recover from the harvesting process. It's normal for trees to lose up to 90 percent of their roots after a digging.
You should only prune some varieties of this tree when it is dormant to avoid pruning away too many leaves. For smaller trees, don't remove too many branches; perhaps one or two that are growing in a bad direction, are rubbing together, or display inward growth.
The point of pruning is to control excessive growth and make the tree look its best.