Black locust is one of the most stubborn stumps in the Carolinas: the heartwood resists rot for years, and cutting the tree can trigger suckers from its roots. Grinding the stump below grade ends the stump, and the root suckers that follow are mowed or treated until the root system gives out.
A native that fights back
NC State Extension calls black locust a native forest tree in the North Carolina mountains that has since spread across the state. It grows thirty to fifty feet tall with a trunk up to three or four feet across, and its branches carry short, paired spines. It fixes nitrogen, which is why it was used to reclaim worn-out ground. It is also open to the locust borer, which NC State says is often fatal. So locust stumps turn up for two reasons: trees killed by borers, and trees cut because they spread where nobody wanted them.
Why cutting makes more locust
Cutting is often what starts the trouble. The Wisconsin DNR explains that damage to locust roots or stems stimulates vigorous sprouting, root suckering and spread, and that neither cutting nor girdling alone kills a clone. NC State describes long underground root suckers that become a maintenance problem. The roots are fibrous with shallow rhizomes. What looks like a grove of separate locusts is often one root system with many stems, so taking down one tree can wake up shoots across the whole patch, sometimes many yards from the stump.
Wood that will not rot
NC State says locust wood is naturally rot resistant, which is why it makes fence posts. Purdue Extension rates the heartwood very resistant to decay and puts its weight close to that of most oaks. The sapwood is another matter; Purdue notes it is completely deteriorated at the ground line. So an old locust stump often has a crumbled outer ring around a hard, sound core that looks barely changed after years in the ground. That core grinds, but it is dense wood and takes its time. The page on old and rotted stumps covers stumps that have sat a long while.
Grinding a locust stump
On the day, the grinder reduces the locust stump and its collar to chips until the hole bottoms out four to eight inches down, spreading out through the flare. That stops sprouts from the stump itself. It does not reach the roots running out across the yard, and on a locust those are the ones that sucker. So grinding is the first half of the job. The second half is cutting every shoot that comes up afterward, low and often, until the roots run out of stored food. Thorny sprouts get woody fast, so do not let them run.
Treating a locust clone yourself
Herbicide can help with a large patch, but only if every stem is included. The Wisconsin DNR says all black locust stems in a clone must be treated for chemical control to work. For cut stumps it lists clopyralid, triclopyr or glyphosate applied from late summer into the dormant season, and for standing stems a basal bark band of triclopyr ester at least six inches high, about a foot above the ground. Read the label, wear the protective gear it lists, and keep spray off trees you are keeping. Your county Extension office can advise on timing. How to stop stump sprouts covers the mowing side.
Locust along fences and field edges
Locust and fences go together. Locust posts are prized because the wood resists rot, and a locust that came up along a wire fence is often grown around the wire by the time it is cut. Before grinding a stump on a fence line, check for wire, staples or nails in the wood and point them out; metal in a stump is hard on a cutting wheel and on anyone standing near it. If a fence panel or wire ever has to come off to reach a stump, you are asked first. Pasture and fence-line stump grinding covers that kind of work.
Common Questions
Why is my black locust stump still hard after years?
Because locust heartwood is very resistant to decay. NC State Extension says the wood resists rot naturally, the reason farmers set it as posts, and Purdue Extension notes that only the sapwood breaks down at the ground line. An old locust stump can keep a sound core long after the outside has crumbled.
Will grinding a locust stump stop the suckers?
It stops sprouts from the stump, but not shoots from the roots, which is where locust suckers usually come from. Keep cutting or mowing those shoots and the roots gradually run out of stored energy. For a large patch, the Wisconsin DNR notes that every stem in the clone has to be treated for herbicide control to work.
Is black locust invasive in North Carolina?
Not in the mountains, where NC State Extension describes it as a native forest tree. It has spread across the rest of the state, and its root suckers make it a nuisance in yards and fields. Whether you call it invasive or not, it behaves aggressively once cut, so plan for follow-up after the stump is gone.
What to Do Next
Email a picture of the locust stump next to a tape, another of the shoots coming up around it, one of the access, and name your town. Call (828) 574-4474.