Tree Killers: Black Locust

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  • Common English name: Black Locust
  • Other names: false acacia
  • Latin (scientific) name: Robinia pseudoacacia

Threat type

150x150 plants

History in Canada

  • introduced from the southern United States as an ornamental tree and as a source of hard, rot-resistant wood
  • still available from nurseries
  • most abundant in southern Ontario but occurs east to Nova Scotia as well as in British Columbia


  • a medium-sized tree (up to 25 m or 80 ft tall) with long compound leaves
    belongs to the Pea family
  • like many other species in the Pea family, it has nitrogen-fixing bacteria in its roots enabling the tree to grow vigorously in poor soil
  • reproduces by root suckers to form dense clones of interconnected trees
    in spring the trees produce large, drooping clusters of fragrant, white flowers
  • large, hanging, multi-seeded pods form in the summer and remain on the tree until the next year
  • seeds rarely germinate although they are produced in large numbers
    branches contain pairs of short, sharp spines
  • prefers open areas with well-drained soil and lots of light but tolerates a wide range of growing conditions
  • stumps will re-sprout vigorously if cut

Impact on Trees

  • may grow in dense stands in open woodland, forest openings, and forest edges
  • suppresses native tree seedlings due to shade
  • enables invasion by other non-native species by enriching the soil with nitrogen

What can be done to control this tree killer?

  • cutting or girdling stems followed by herbicide application to the cut stems or later removal of sprouts that develop after cutting
  • several years of control may be needed since stumps can resprout one or more years after treatment

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