Scotch Thistle

Onopordum acanthium

Asteraceae (Sunflower family)

Class B Noxious Weed

Control or Containment Required

Scotch thistle was brought to the U.S. as an ornamental in the late 1800s. It is now a widespread invader of roadsides, ditch banks, rangeland and pastures. It is a serious problem on rangeland where it reduces forage and limits land utilization for livestock and wildlife.

An upright, branched, robust biennial, Scotch thistle often grows more than 8 feet tall, covered with sharp spines and winged stems. It typically lives two years, its first year as a rosette with a taproot. The second year the plant bolts then flowers from June well into the fall months.

Scotch thistle reproduces by seed. Each plant can produce up to 40,000 seeds, which can remain viable in the soil up to 40 years.