All Species

Creeping Thistle / Canada Thistle

Cirsium arvense
Jan Samanek, Phytosanitary Administration, Bugwood.org

Why is it a problem?

  • Spiny, aggressive invader that outcompetes native plants for nutrients and water, poisonous to grazing animals, and can increase forest fire severity.
  • Roots grow 18 feet per year; spreads by seeds, stems and root fragments.
  • Produces 40,000 seeds per plant; seeds viable for 20 yrs.
  • Seeds dispersed by wind, water, animal droppings, on clothing and equipment, and in contaminated hay and crop seed.
  • Allelopathic (produces chemicals that inhibit growth of other plants) and alters native pollinator habits.


How do I manage this plant?

  • Avoid disturbing soil, which provides a foothold for establishment; where disturbance takes place, reseed with native species Avoid cultivation where Canada thistle is present, as this will stimulate production of horizontal stems and new shoots.
  • Remove flowers before they produce seed.
  • Extremely difficult to control once established, and requires a combination of mechanical, cultural, and chemical control.
  • If discovered, recommend rapid response with chemical control.

More info on species biology