A perennial weed is any weed capable of surviving for three or more years Perennial weeds are characterized by vegetative reproduction. Perennial weeds may or may not reproduce by seed. They always, however, have the potential to reproduce by vegetative means. Description of Canada Thistle Canada thistle has an extensive, deep root system. Stems are 2 to 5 feet tall, grooved, and branch only at the top.
Stems are slightly hairy when young, but increase in hairiness with maturity.
Leaves are slender, smooth, and have crinkled edges with spiny margins. There are many compact rose-purple flowers surrounded by tight bracts. Canada thistle primarily spreads by an underground root system. It often grows in dense patches in fields or pastures. Control of perennial weeds may require a combination of all these methods.