Canada Thistle — Cirsium arvense — Family: Asteraceae — Aster

Canada thistle is a creeping perennial that always colonizes in patches. Plants can reach 1-3 feet high. Canada thistle has an extremely well developed creeping root system that can grow several feet deep.

Leaves are smooth on the surface and deeply lobed with spines on the margins. Flowers are produced in 3/4" diameter purple clusters at the end of the stems in June, July and August.

Canada thistle is often associated with lower maintenance sites such as pastures, fields and road-sides.

Also Known As...

• corn thistle
• cursed thistle
• creeping thistle
• small-flowered thistle
• perennial thistle
• green thistle
• known in Canada as 'thistle'

Elongated	Notches	Whorled	Upright

long, narrow, lobed leaves; smooth leaf surface, spines on margin

grows 1-3 feet tall if unmowed

purplish flowers grow in clusters

Bull thistle, a biennial, is often confused with Canada thistle but can be distinguished by the profuse hairs present on the upper leaf surface. Bull thistle will often appear as a single specimen, whereas Canada thistle will almost always be present with several daughter plants.

Links:

• Bull Thistle (Cirsium vulgare)

Canada thistle is usually associated with low maintenance turf. Hand weeding is not an effective control method for this weed due to the well developed, deep root system. Improving the growing conditions for the turf by increasing nitrogen fertilization and providing consistent mowing at 2-3" may reduce infestation over several seasons.

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