Canada thistle. Photo: Caleb Slemmons, National Ecological Observatory Network, Bugwood.org
About Canada thistle
Canada thistle is one of the noxious weeds in Maryland.
Life cycle
Canada thistle (Cirsium arvense) is an invasive perennial broadleaf weed with a deep root system.
Growth habit
Clump-forming; grows to 2 - 5 ft. high; leaves long and narrow, alternate, irregularly lobed with spiny margins; spineless stem.
Reproduction
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.
Cultural control
Keep vacant areas covered with turf or ground cover; maintain soil fertility appropriate for the growing crop.
Related information
Additional resources
Plant Invaders of Mid-Atlantic Natural Areas
(PDF) Weeds Gone Wild: Alien Plant Invaders of Natural Areas
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