|Conditions:||Sun to light shade, most soils|
|Vegetative Spread:||Aggressively spreading via rhizomes|
Cirsium arvense, known as Creeping Thistle or Canada Thistle, is a species of the genus Cirsium, native throughout Europe, Asia and northern Africa.
It is a tall herbaceous perennial plant, forming an extensive underground root system that sends up numerous erect stems each spring, reaching 1-2 m tall; the stems often lie partly flat by summer but can stay erect if supported by other vegetation. The leaves are very spiny, lobed, up to 15-20 cm long and 2-3 cm broad (smaller on the upper part of the flower stem). The inflorescence is 1-2 cm diameter, pink-purple, with all the florets of similar form (no division into disc and ray florets). The seeds are 4-5 mm long, with a downy pappus which assists in wind dispersal.
It is a nuisance weed in its native area, and a very serious invasive species in many other areas of the world.
Cirsium species, are, for the most part, not toxic; however, the leaves are considered bitter and therefore rendered inedible; the taproot is considered the most nutritious. In Scotland (especially Fife) they are considered a delicacy, albeit a somewhat unusual one.
This plant is extremely difficult to control, as it can regrow from fairly small root fragments and is resistant to many herbicides.
- Pre-emergents can help prevent the plant from becoming established, but it is generally more often encountered as a perennial problem.
- Contact herbicides are only partially effective. Glyphosate in particular needs to be repeatedly applied.
- Mowing is effective over time, if done regularly.
- Goldenrods are allelopathic to this plant. Smothercropping of buckwheat and winter rye will also weaken the plant considerably.
- Pulling must be done repeatedly over a long period, but will eventually kill the plant. Gloves should be worn.
- Smothering techniques such as paper mulch barriers are quite effective.
- Canada thistle should never be added to a cold-composting system. All parts of the plant should be burned, thrown away, or put into high-temperature composting systems.