Poison Hemlock

poison hemlock flowers

Poison Hemlock

Conium maculatum

Information Sheet (PDF)


Colorado List C - Control Recommended


General

  • All parts of this plant are poisonous to humans and animals
  • Native to Eurasia, introduced to North America as an ornamental
  • Parsley family (Apiaceae)


Common Names

  • Poison hemlock, Poison parsley


Habitat

  • Biennial forb
  • Colony forming
  • Found along streams, ditch banks and pasture borders


Plant


Vegetation

  • Leaves shiny, green and finely divided, with a musty odor, 1-16 inches long
  • Plant 4-10 feet tall
  • Stems are lights green with purple spots


Roots

  • Long, white taproot


Flower

  • April - July
  • Small, one twelfth to one sixteenth of an inch across
  • White, 5 petals, umbrella-like cluster


Seed

  • Can remain dormant in soil for up to 3 years
  • Over 38,000 seeds per plant
  • Pale brown


Seedling

  • Rosette resembles wild carrot
  • Young plants are purple tinged


Reproduction

  • Seed


Control


Biological

  • None


Chemical


Cultural

  • Prevention
  • Removal - Must be repeated as new plants germinate


Mechanical

  • Burning - N/A
  • Grazing - N/A - Poisonous to livestock
  • Mowing - Prior to flowering. Mow every three to four weeks. Works best when combined with herbicide treatments.


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