Adams County
CO Noxious Weeds

Home > CO Noxious Weeds > Canada thistle

Canada thistle

(Cirsium arvense)


Canada Thistle

Identification : Originally from Eurasia, Canada thistle is an aggressive, colony-forming, creeping perennial weed that develops from seed or vegetative buds in its root system. Horizontal roots(rhizomes) my extend 15 feet and vertical roots may grow 6 to 15 feet deep.

Canada thistle rosette

It emerges from its root system in mid- to late-spring and forms rosettes. Plants grow from 1 to 4 feet in height.Flowers are unisexual, small and are lavender to purple(sometimes white) in color. Leaves are green, alternate, crinkly, and have well developed sharp spines along their edges. Canada thistle begins to flower in late spring to early summer and may produce, on average, 1,000 to 1,500 seeds per plant.


Canada Thistle Dispersing Seed


The small, dry, single-seeded fruits(achenes) have a white feathery structure attached to the seed base. Seeds may be transported long distances by wind, water, by being attached to animals, clothing, farm equipment and other vehicles, or with contaminated crop seed. Canada thistle is common throughout Adams County.


Disclaimer | EEO | Ask an Expert | Webmaster - Last updated 9-3-08

Extension Home | CSU Home

CSU Extension Home