Canada thistle or Canadian thistle is a noxious weed commonly found in residential gardens across North America. This perennial plant features tiny unisex flower heads that are usually purple, with hairy stems and leaves, an extensive root system and grow in a variety of soils, which makes removing it even harder. Canada thistle spreads even with split roots and its seeds remain viable in the soil for up to 20 years. Although hard to remove, with a little perseverance and determination, you can rid your lawn of this weed.
Find the weeds on your lawn and their stage of development so you make a control strategy accordingly. Established plants feature purple flower heads, while younger ones are low-lying and feature pointed leaves with serrated edges.
Wear gloves, a long-sleeved shirt and full pants and snip off the plant at soil level with a lawn mower, shears or string trimmer. Snip the weeds in spring, before the plant sets seeds. The stress of being cut encourages the roots to send up new growth soon after, so you need to cut repeatedly for several seasons, sometimes as many as seven, to weaken the roots and stop regrowth.
Dig up individual plants if the infestation is small. Using a narrow spade, start digging a foot from the base of the plant. Extend the mark to form a circle around the base, and then dig deeper in the soil at an angle. Push the shovel deeper and lift the plant out of the soil, along with its root ball. Wear gloves and remove broken pieces of roots that remain in the soil to prevent the weed from growing again.
Apply a systemic herbicide to the foliage in spring after the buds appear or before regrowth in fall. Make sure it contains glyphosate, dicamba or clopyralid chlorsulfuron. Do not disturb the plant for up to a week to ten days after application. Repeat application for stubborn plants. Follow label directions for herbicide application dosage and precautions as they contain toxic chemicals.
Collect all the plant pieces in a garbage bag, knot firmly and dispose immediately to prevent any seeds from spreading or blowing to other parts of the lawn with the wind.