Invasive Plant Guide: Canada Thistle

 
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Canada Thistle Flower

Cirsium arvense

Identifying characteristics

  • Flower color: pink-purple, very fluffy
  • Flowers: June April to October
  • Stems: erect stems each spring, the stems often lie partly flat by summer
  • Plant height: typically 2 to 3 feet tall in our area (can reach 6 feet)
  • Leaves: very spiny, lobed, up to 6-8 inches long and ¾ to 1½ inches wide
  • Seeds: ¾ to 2 inches long, with a downy pappus which assists in wind dispersal
  • Growth habit: perennial

Occurrence

Open disturbed sites, roadsides, fields, pastures, hillsides, rangeland, forest openings. Also found along stream banks and in gardens. Does not tolerate deep shade or constantly wet soils.  Tolerates a wide range of soil types, but grows best in moist soils.

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Canada Thistle Plant & Flower

Notes

Plant spreads via rhizomes (underground roots) and by seed. Perennial patches of Canada thistle are found as a clump of many interconnected plants. All other thistles in our area grow as a single stemmed plant. It has no trouble sending rhizomes in a maze directly under river rock.

More Info

California Department of Food & Agriculture
www.cdfa.ca.gov/phpps/ipc/weedinfo/cirsium.htm