Canada Thistle


Date: July 28th, 2011

Canada thistle (Cirsium arvense) is a persistent, creeping perennial weed that can be difficult to control. Some people refer to this plant as a “pricker bush” while others have more of a derogatory phrase to decipher the prickly plant. If you are one of these people, you aren’t alone in your distaste for this weed; this plant has proved to be a menace to the northern half of North America.

Unlike other weeds that limit their damage to only your lawn and garden, this weed has the nerve to cause harm to you too. The prickly thorns can serve as a harsh reminder to stay away from this plant.

So how do you remove Canada thistle from your lawn? Read on for further information.

Canada Thistle


Canada thistle is a spiky plant that can grow four feet tall (sometimes larger). It has a smooth stem but its spiny leaves are what the plant is renowned for. Prickly pink flowers will appear later in the growing season.

Growing Conditions

Canada thistle infestations usually grow in areas with disturbed ground. This can include ditch banks, overgrazed areas, and abandoned sites. This weed can be especially frustrating for farmers as the plant can reduce animal forage consumption. Livestock will usually not feed near infestations due to the chance of an accidental bite of prickly vegetation.

In a period of 1-2 years, Canada thistle can colonize an area of 3 to 6 feet. The plant is rather hardy and can grow in various soil types. The plant does best in deep, well-aerated, and cool soils.

Canada Thistle Root

The plant will emerge in late spring and begin to form rosettes before flowering in early summer. As mentioned earlier, the plant has an extensive root system. Studies have found that horizontal roots may extend 15 feet or more and vertical roots may grow 6 to 15 feet deep! For an example of the roots, check out the picture above.



Canada Thistle

The key to controlling this plant is forcing the plant to use stored root nutrients. Eventually the plant will run out of stored nutrients and die. Unfortunately, due to the deep root system this will require multiple control methods and efforts. This is not a quick fix if the plant has been allowed to grow for a period of time; in most cases in will take years.

Chemical control can be effective with multiple applications and combined with cultural and/or mechanical control. Research at Colorado State University shows that Tordon 22K (picloram), Milestone (aminopyralid), Transline (clopyralid), Banvel/ Vanquish/Clarity (dicamba) and Telar (chlorsulfuron) are effective against Canada thistle.

Bonide Chickweed, Clover & Oxalis Killer has also proven effective in control.

Mowing can be an effective tool if combined with herbicide treatments. It should be done at one-month intervals over several growing seasons.

Mechanical control can be a bit tricky with this plant. Due to its prickly exterior, always use thick gloves and a long sleeve shirt when dealing with it. The plant can be dug out using a shovel or spade but removing the entire root will be almost impossible. Root remnants will result in the plant reemerging in a short period of time or next growing season. Mowing the plant before digging out the root can result in less of a chance of getting pricked. Gather all parts of the plant and properly dispose of them.



While many people think that this plant has no use to anyone, the seeds actually serve as a very important food for goldfinches and linnets. Butterflies, moths, and aphids also use this plant as a source of nutrition.


If you have any further questions, email them to, or visit your local CountryMax store today!




Root picture provided by Purdue University Department of Botany and Plant Pathology


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