No photo available yet
Submit a photoCanada Thistle
Cirsium arvense
⚠️ NOXIOUS — despite the name, not native to Canada (it's from Eurasia). Alberta's most widespread and stubborn perennial weed, with spiny-leaved stems 30–150 cm tall and small pink-purple flower heads in clusters. Spreads aggressively by deep horizontal rhizomes — pulling rarely kills the plant, and root fragments regrow. Dioecious: male and female on separate plants, so some patches don't set seed.
Quick Facts
Distribution
Ubiquitous across Alberta — pastures, cropland, ditches, yards
Light
Full sun
Bloom Time
June–Aug
Soil
Adaptable — prefers moderately moist agricultural soils
Water
Moderate
Growing & Cultivation
Propagation
DO NOT PROPAGATE. Control: repeated mowing or herbicide in fall when roots pull nutrients down. Biological control stem-mining weevils (Hadroplontus litura) and rust fungi available for large rural infestations.