Canada thistle

(Cirsium arvense)

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.

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.

 

 

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.

 

Managing Canada Thistle

Additional Information

Information Sheet - Canada Thistle

CSU Fact Sheet # 3.108 - Canada Thistle

 

Kelly Uhing, Colorado Department of Agriculture

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Last updated 02-20-07