Weed of the Month: Canada thistle

Weed of the Month: Canada thistle

Canada thistle is a widespread invasive weed that’s a common problem in cultivated fields and pastures. It’s a perennial plant that spreads both by seed and by creeping horizontal roots (called rhizomes). This weed is very difficult to kill.

Canada thistle has multiple small pink to purple flowers that are bristly and 1/2 inch long and wide. The plants are usually 3-5 feet tall with green leaves that are glossy on the upper surface and woolly on the underside. The leaves are irregularly lobed with sharp spines. Seeds have tufts of tan hair loosely attached to the tip and are dispersed by the wind. They can remain viable in the soil for up to 20 years.