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.
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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.
- annually hand pull or dig rosettes and adult plants, dry in sun or bag for landfill
- if thistle has bloomed, clip off flowers, buds, and seed head
- 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.
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.