Swamp Thistle Cirsium arvense

Canada Thistle is an upright herbaceous perennial weed in the Asteraceae (daisy) family. It is native to Europe, Asia, and Africa where it is found in wet meadows, swamps, bogs, and moist woodlands. It was introduced to the United States in the 1600's and is considered a noxious weed in 43 states including North Carolina. It is found in most of the US and southern Canada. Stems are upright up to 6' tall, grooved, and just a few hairs or none. The stems are also slender and branched only at the top. The leaves are poky like other thistles and it has purple pink flowers that appear in the summer. Canada thistle has male and female flowers on separate plants, but the flowers look similar to each other. Male flowers will not produce seeds, female flowers are fragrant. 

It prefers moist soil, sun to partial shade but withstands a variety of soil conditions and is most commonly found in disturbed areas, clearings or agricultural sites. Canada thistle spreads through both seeds and budding from underground roots. 

The common name Creeping thistle comes from its tendency to spread by lateral root growth, or its seeds are wind dispersed allowing it to rapidly form dense stands that can shade out native plants.  Its root system can extend more than fifteen feet out and six feet down from the plant, making management difficult as new plants come up from the roots. 

Thistles are a great option in your meadow garden or naturalized area when looking for a plant to attract pollinators and seed-eating birds. However, it is considered a noxious weed in North Carolina and in many areas of the United States. Please consider planting the Native Alternative Plants shown in the left sidebar. Canada thistle should not be introduced into the garden. 

Insects, Diseases, and Other Plant Problems:  Canada thistles extensive and aggressive root and shoot system coupled with its prolific seed production make it very difficult to manage. Consistent repeated mowing and/or hand pulling can deplete the root system storage over a series of years. Biological and chemical management may need to be used in conjunction with mechanical measures.