Canada thistle

Canada thistle

Cirsium arvense

Canada thistle brochure (PDF)

Why is Canada thistle a problem?

Canada thistle rapidly establishes and spreads quickly, replacing native plants. It grows in circular patches, spreading up to 10-12 feet in one season. It spreads quickly by rhizome and seed production. 

Canada thistle poses an economic threat to the agriculture industry by reducing crop yields and out-competing native plants. 

Recommendations for controlling Canada thistle

Chart for controlling Canada thistle

Recognizing Canada thistle

Canada thistle is a perennial herbaceous plant that is commonly found in pastures and croplands. 

It grows two to five feet tall with slender grooved stems that branch out at the top. This plant spreads by rhizomes and seeds. 

Flowers are purple-pink, in clusters one-half to three-quarters of an inch in diameter and bloom from June to October. Leaves are alternately arranged and lance-shaped to narrowly oval. Stems begin as a rosette and grow upright after two to four weeks.