About Canada thistle
Canada thistle (Cirsium arvense) is an invasive perennial broadleaf weed with a deep root system.
Clump-forming; grows to 2 - 5 ft. high; leaves long and narrow, alternate, irregularly lobed with spiny margins; spineless stem.
Spreads by fleshy, creeping rhizomes; lavender disk flowers followed by fluffy pappus capable of floating long distances in the wind; 680 seeds produced per stem; seeds remain viable in soil from 10 - 20 years.
Conditions that favor growth
Infertile areas without plants covering soil.
Keep vacant areas covered with turf or ground cover; maintain soil fertility appropriate for the growing crop.