Mature Plant

Description: Canada thistle is a perennial reproducing by seeds and underground roots. The roots extend several feet deep and some distance horizontally, often forming dense patches. The mature plant will reach a height of 2 to 5 feet. The upright sterns are grooved, slightly hairy when young, increasingly hairy as they mature, and branched at the top. The leaves are alternate, have crinkled edges, spiny margins, and are somewhat lobed. The flower heads are numerous, compact, and 3/4 inch or less in diameter. The flowers are reddish-purple to purple and are surrounded by bracts without spiny tips. Male and female flowers are usually borne on separate plants. Flowering occurs from June throughout September with seed maturing 8 to 12 days after full bloom. The seeds are gray to brown, smooth, slightly tapered, 3/16 inch long, and have a ridge around the blossom end.

Seedling

Distribution: Canada thistle can be found in all crops, pastures, waste areas, and along roadsides throughout Minnesota. Canada thistle is the most prevalent and persistent broadleaf weed in the state.