Black locust trees (Robinia) are famous for their vigorous growth and their knack for developing those impressive double crowns. But here’s the good news for low-maintenance gardeners: for the most part, you can just let them do their thing! Regular pruning isn’t usually a requirement, though there are a few specific situations where you’ll want to grab your shears or a chainsaw.
Generally, No Pruning Required
Even though the Black locust has a reputation for incredibly fast growth, it’s not a tree that needs a yearly haircut to stay healthy. In a natural garden setting, you can mostly leave it alone.
Reasons to Prune
That being said, there are times when a light trim—or even a major cutback—is necessary. You’ll want to consider pruning if you need to:
- Keep the tree’s size in check,
- Remove overhanging or hazardous branches,
- Clean up storm damage,
- Deal with pests or diseases.
Pruning to Control Growth
If your Black locust is starting to take over the yard, regular heavy pruning can help keep its size manageable. You can cut the tree back to your desired height, but keep in mind that these trees are resilient—they will keep pushing out new shoots and branches. If you’re looking for something permanently smaller, you might want to look into dwarf varieties like the Globe locust.
Removing Problem Branches
Safety first! If branches are hanging over the neighbor’s fence, blocking public sidewalks, or posing a threat to your roof, it’s time to trim them back. You should also clear out any branches that have cracked or snapped during a heavy storm to prevent them from falling unexpectedly.
Diseases and Pests
If your tree is struggling with diseases or a pest infestation, a hard prune can actually help save it. Especially with fungal issues, you’ll want to cut away all affected areas generously to stop the spread. In severe cases, a radical “reset” cut might be the only way to nurse the tree back to health.
Special Care for Globe Locusts
The Globe locust is a popular variety because it naturally grows in a tidy, round shape. While it maintains this look pretty well on its own, you can snip off any “stray” branches whenever you like if you want that perfectly manicured, spherical look.
Pruning a Black Locust Bonsai
If you’re growing a Black locust as a bonsai, the rules change—regular pruning is essential to keep that miniature scale. You’ll need to consistently trim back any branches that disrupt the silhouette to keep your bonsai looking its best.
When it’s time to repot, I also recommend a root prune. Clear out any old, dried-up roots and give the healthy ones a light trim. This helps keep the tree’s overall growth restricted and manageable for a small container.
The Best Time to Prune
For general maintenance, it’s best to prune in the fall or winter. Just be careful not to snip off any developing buds, flowers, or seed pods if you want to enjoy the tree’s full display next season.
Safety First: Watch Out for Thorns!
A quick heads-up before you head out to the garden: always protect your hands and skin. Black locusts aren’t just toxic if ingested; they also have very sharp thorns. Make sure you’re wearing heavy-duty gardening gloves and long sleeves before you start cutting!
