- Type
- Spiny tree
- Status in NSW
- North Coast regional priority. In Port Macquarie-Hastings, land managers should limit its spread. Should not be bought, sold or moved.
Black locust is a fast-growing, spiny tree once planted in gardens and used as rootstock for golden robinia. It spreads by suckering from its roots, forming spiky thickets, and every part of it is poisonous to people and livestock.
How to identify it
Black locust usually grows 10 to 15 metres tall. Look for:
- leaves up to 15 cm long with 11 to 21 oval leaflets with notched tips, which turn yellow in autumn as the tree drops them
- pairs of sharp spines 5 to 25 mm long at the base of the leaves
- drooping clusters of white, strongly scented, pea-like flowers
- flat, smooth pods 3 to 8 cm long that turn from green to brown
- bark that is smooth on young trees and deeply furrowed on old ones
Where it grows
Black locust grows best in full sun and well-drained soil. It turns up along waterways, roadsides, in urban bushland and in old gardens, often where a grafted ornamental tree has been cut down and the rootstock has taken over.
Why it's a problem
- Its thickets crowd out native plants, and its leaves release chemicals that stop other plants growing.
- All parts of the plant are poisonous to people, especially the pods, seeds, bark and leaves. If someone is unwell after eating it, call the Poisons Information Centre on 13 11 26, or 000 in an emergency.
- It is poisonous to horses, cattle and sheep. Horses are the most affected.
- Thickets block access and reduce food and shelter for native animals.
How to control it
Black locust is hard to kill because of its roots. Combine methods and keep checking treated sites for several years.
- Remove young plants and seedlings early, wearing gloves. Suckers are sharp and regrow if snapped.
- Don't just mow, slash or dig around it. Disturbing the roots makes it sucker vigorously.
- Treat cut stumps straight away (within 15 seconds) to stop resprouting.
- Basal bark spraying from ground level to at least 30 cm high, or stem injection, works on larger stems.
- For regrowth, wait until it is at least 1 metre tall before treating.
Always follow the herbicide label, and ask Port Macquarie-Hastings Council's weeds officer for advice on large infestations.
Safety and disposal
- Wear thick gloves and eye protection because of the spines.
- Keep children and livestock away from pods and cut branches.
- Don't use the roots or stems as mulch or fill, as root pieces can regrow.
Stopping it coming back
- Don't plant black locust or golden robinia.
- Avoid moving soil or machinery from infested sites.
- Plant dense native vegetation. Black locust seedlings struggle in shade.
