Canada Thistle

Cirsium arvense

young canada thistle flowers
 Image credit: SSISC

Characteristics

Canada thistle, a terrestrial herbaceous perennial in the Asteraceae family, is an open land invasive that prefers disturbed upland areas as well as wet areas with water fluctuations. Canada thistle can be found in clay to gravelly soils.

  • typically grows 3 to 5 feet tall
  • stalk-less leaves around 6 inches long, wavy, lobed leaves with yellow spines at each lobe
  • stem is spineless, unlike leaves and bull and European marsh thistle
  • pink, white, or lavender colored flowers with flat bracts and pointed tips that bloom in June
  • seed is fluffy, white tufts of hair that is wind dispersed

Another key characteristic of Canada thistle is the fuzzy underside of the leaves.

For more information visit MISIN.

 

KISMA Management Practices

Canada thistle forms extremely extensive root systems that need to be repeatedly damaged to keep them from growing back. These root systems can spread very aggressively and can expand from 6 feet wide to 10 feet wide in one growing season.

  1. annually hand pull or dig rosettes and adult plants, dry in sun or bag for landfill
  2. if thistle has bloomed, clip off flowers, buds, and seed head
  3. be sure to dispose of clippings in a bag

Note: It is important to hand pull plants repeatedly to eventually exhaust the seed source and deplete populations. It is also important when disposing of clippings to not spread them anywhere else, as they will seed wherever they can.

 

Native Alternatives

Species such as native swamp thistle, swamp milkweed, and Joe Pye weed, are all great alternatives to Canada thistle. These species are tall herbaceous perennial flowers that are extremely similar to Canada thistle. All of these would be great choices for replanting areas where Canada thistle has been removed.

canada thistle flower and stem

(image credit: WSNW) flower and stem of Canada thistle with spines

canada thistle fluff

(image credit: WSNW) Canada thistle fluffy fruiting body

canada thistle spiny leaf

(image credit: WSNW) spiny leaf of Canada thistle (WSNW)

canada thistle flowers

(image credit: WSNW) Canada thistle flowers

Sources

"Canada thistle". Minnesota Department of Agriculture.

"Canada thistle (Cirsium arvense)". MISIN, 2021.

"Canada thistle". Washington State Noxious Weed Control Board (WSNW).

"Canada Thistle". Sea to Sky Invasive Species Council (SSISC), 2015.