Poison Hemlock

Conium maculatum

Poison Hemlock

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
Is this Weed Toxic?:

humans, livestock


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/parsley) 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, hairy, and doesn’t have purple blotches on the stems.

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 Does it Reproduce?

Poison hemlock reproduces by seed.

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. Do not burn plants due to the toxins within plant parts. Also, due to the plants toxicity, do not allow animals to graze live or dead poison hemlock plants.

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. Toxins will remain potent in dried plant material. Never put pulled plants in the compost or leave them where children or livestock might eat them. Removed pulled plants from site, bag and put in the trash. Monitor sites for resprouts and seedlings as seeds will readily germinate on disturbed ground.

BIOLOGICAL CONTROL

See the WSU Integrated Weed Control Project for further information.

Herbicide Control

Always read and follow the label instructions before applying any herbicide product. The best time to spray poison hemlock is in the spring, when the plant is still young and the leaves are just a basal rosette, before it forms a stem and flowers. 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 brochure in Spanish on poison hemlock.

See our postcard for early detection information about poison hemlock.

See our press release for more information about poison hemlock (Conium maculatum).

See our Written Findings for more information about poison hemlock (Conium maculatum).

Clallam County NWCB Fact Sheet on poison hemlock

Pierce County NWCB Fact Sheet on poison hemlock

Lincoln County NWCB Fact Sheet on poison hemlock

Island County NWCB Fact Sheet on poison hemlock

King County NWCB Fact Sheet on poison hemlock

King County NWCB Fact Sheet on poison hemlock in Spanish

Thurston County NWCB Fact Sheet on poison hemlock

Whatcom County NWCB Fact Sheet on poison hemlock

Jefferson County NWCB Fact Sheeton poison hemlock

Cowlitz County NWCB Fact Sheet on poison hemlock

Mason County NWCB Fact Sheet on poison hemlock

Control Options for poison hemlock from Whatcom County NWCB

WTU image page on poison hemlock

Additional Photos