Scotch Thistle

scotch thistle plant

Scotch Thistle

Onopordum acanthium

Information Sheet (PDF)


Colorado List B - Control required in Jefferson County

General

  • Biennial
  • Family: Sunflower (Asteraceae)
  • Native to Europe and eastern Asia


Habitat

  • Found in rangelands, disturbed areas and right-of-ways
  • Thrives in moist areas


Plant


Vegetation

  • Covered with dense hair
  • Leaves are up to 2 feet long and 1 foot wide
  • Mature plants are 12 feet tall
  • Stems have spiny wings


Roots

  • Tap root


Flower

  • Color: violet
  • Season: mid-June through September
  • Size: 1 to 2 inches wide
  • Spiny bracts


Seed

  • May remain viable in soil for more than 30 years
  • One plant can produce 20,000 to 40,000 seeds
  • Seeds germinate in the fall and spring


Seedling

  • Forms dense patches
  • Rosettes can grow 6 feet wide
  • Rosettes form the first year and bolt early May to June of the next season


Reproduction

  • Seed


Control


Biological

  • None


Chemical


Cultural

  • Prevention – maintain health of site using good grazing management and keeping good cover
  • Removal
  • Re-vegetation of highly disturbed sites


Mechanical

  • Burning - May cause seeds to germinate
  • Grazing - N/A
  • Mowing - When used with other methods


More Information


Use all chemicals according to the manufacturer's label. No specific recommendation or endorsement is made or implied by listing methods or products.