poison hemlock

Conium maculatum


Family: Apiaceae

Other common names: carrot-fern, fool's-parsley, spotted hemlock

Weed Class: B

Year Listed: 1988

Native to: Europe, Asia and Northern Africa

Toxic: humans, livestock

Other Legal Listings:

additional photos



Why is it a noxious weed?

The entire plant is toxic to animals and humans, containing the poisonous alkaloid coniine and other alkaloids. Poison hemlock can quickly infest large areas of pasture as well as open waste places.

How would I identify it?

General Description: Poison hemlock is a very tall biennial plant that can grow up to 12 feet in height. It grows into a rosette the first year--a cluster of leaves growing on the ground and then flowering stems the next year.

Flower Description: Flower are small and white and occur in 4 to 8 inch umbrella shaped clusters.

Leaf Description: Leaves are fern-like, toothed, finely divided and have a strong odor when crushed.

Stem Description: Stems are hollow, hairless and have noticeable purple blotches.

Fruit/Seed Description: Seed hairless, egg-shaped and about 0.09 inches (2 mm) long with prominent ridges.

May be confused with: Other plants in the Apiaceae (carrot) family when young. From a distance, wild carrot (Daucus carota), a Class C noxious weed, may be confused with poison hemlock, although wild carrot is smaller and doesn’t have purple blotches on the stems.

How does it reproduce?

Poison hemlock reproduces by seed.

Where does it grow?

Poison hemlock prefers rich, moist soil, but is highly adaptable to other conditions. Please click here to see a county level distribution map of poison hemlock in Washington.

How do I control it?

General Control Strategy

Always wear gloves and protective clothing if handling poison hemlock as all parts of this plant are toxic.

Mechanical Control

Digging up small infestations and removing the entire taproot is effective. Mowing is ineffective as plants will re-sprout, sending up new stalks in the same season mowing occurs.

Herbicide Control

Please refer to the PNW Weed Management Handbook, or contact your county noxious weed coordinator.


For more information

See our brochure on poison hemlock.
See our postcard for early detection information about poison hemlock.
Thurston County Noxious Weed Control Board fact sheet
WTU image page on poison hemlock
See our recent press release for more information about poison hemlock (Conium maculatum).

Additional Photos



Poison hemlock inflorescence


Poison hemlock growth


Poison hemlock inflorescence


Poison hemlock stem


Young plant


Poison hemlock leaf


Dying plant


Developing seeds


Poison hemlock plants


infestation of poison hemlock rosettes


emerging leaf


stem with purple markings




seeds from the previous year


in bloom


open flowers


blooming plants


seedlings and young rosette


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