Botanically known as Cirsium arvense, Canadian thistle, or Canada thistle, is a purple pest that invades lawns and gardens across the United States. This hardy perennial plant has an extensive root system and small flower heads. At first glance, Canadian thistle plants appear to be attractive, but they become a gardener's nightmare with time. These noxious weeds survive freezing temperatures and grow in any type of soil. However, with a little persistence, you can kill Canada thistle and eradicate it from your lawn.
Walk through your lawn to identify this invasive pest. It is easily recognizable when in bloom due to its violet flower heads, but the less established plant is low-lying and deep green, with sharp pointed leaves that have serrated edges. Young plants have a short stem, which explains why the leaves sprout outward from the center, just above the ground. Run your finger against the base of each leaf to feel the thistle.
Wear gloves and dig the ground around small patches of Canadian thistle with a hand shovel to remove it. Make sure you remove as much of the root system as possible. Dig deeper to pull out taproots that may have escaped the shovel to prevent the thistle from growing there again. Canadian thistles propagate by taproots and seed distribution.
Collect the thistle in a plastic bag, knot it tightly to prevent seeds from escaping and discard appropriately.
Set your lawn mower at the lowest setting and mow the area where Canadian thistle is widely distributed. Do this before the flower heads bloom to prevent seeds from spreading. Cutting the plants before the seeds mature eliminates their chance of growing and spreading in the garden.
Spray or pour herbicide that contains glyphosate, dicamba, clopyralid chlorsulfuron, or any commercial weed killer specifically formulated for Canadian thistle over the freshly mowed area. Make sure there are no other plants nearby if pouring the herbicide, as it could damage them. Read manufacturer's instructions and follow directions and precautions.
Burn large pieces of rural land covered with thick and invasive growth of Canadian thistle to completely remove it. This method is practiced by farmers between harvesting and planting, so the ground is free of these pests that compete with growing plants for nutrients.