Invasive Plant Guide: Canada Thistle
Canada Thistle Flower
- 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
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.
Canada Thistle Plant & Flower
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.
- California Department of Food & Agriculture