How to Kill Canadian Thistle


Is your yard being invaded by those common purple thistles? Canadian thistle (Cirsium arvense), often referred to as Canada thistle, can appear to be a very attractive flowering plant at first glance, but it can become a landscaper's nightmare. This noxious weed is very invasive and grows easily in many areas of the United States. You can remove this weed from your yard and garden with a little persistence.

Things You'll Need

  • Garden hand shovel
  • Lawn mower
  • Herbicide

Eradicate Pesky Canadian Thistle

  • Identify the immature weed. Canadian thistle is easily recognizable with its dusty violet blossoms when in full bloom, but less obvious when it is just getting established. Look for small, deep green clumps in the middle of your yard or garden. Upon close inspection, notice the long, sharply pointed leaves with serrated edges. The leaves will appear to be sprouting outwards from the center slightly above the ground, as the young plants to not display much stem. The sharp thistles can be felt along the base of each leaf.

  • Remove these immature thistles with a simple hand shovel if there are only a few in your yard. Dig a few inches around the visible roots to ensure removal of the complete root system. Carefully pull out any taproots that have escaped your shovel. These taproots can reach up to three feet in mature thistles. Complete removal of the whole plant, including the roots, is necessary to successfully eradicating this weed.

  • Mow down areas where Canadian thistles have become widely disbursed. Mow before the plants have a chance to bloom. Canadian thistles propagate by means of seed distribution and taproots. It is important to cut the plants before the seeds have a chance to mature.

  • Apply an herbicide formulated for use on Canadian thistle over your freshly mowed area as soon as possible. A systemic herbicide containing glyphosate, such as Rodeo or Roundup, can be used on areas that contain desirable plants. Broadcast this over the whole area or just spray directly onto the exposed thistle. Reapplication may be necessary. Follow all directions and precautions on label when using herbicides.

  • Burn off large areas of rural land that have been taken over by Canadian thistle. A controlled burn may be the only way to ensure complete removal of this weed in situations where it has become very thick and invasive. Farmers often burn fields between harvesting and planting to allow their crops the best chance for success in the fight against Canadian thistle. Contact your local fire department concerning laws and regulations regarding controlled burns in your area.

Tips & Warnings

  • Wear thick gloves when handling Canadian thistle.

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