Identification and Reproduction

Identification: 

• Poison hemlock is a toxic biennial in the Apiaceae family (carrot).
• Puts off an unpleasant odor when crushed. 
• This plant typically grows between 1 to 3 m tall. 
• Hollow stems are green with purple reddish blotches and are hairless.  

• Leaves are light green, triangular and fern-like. 

• Flowers are small and clustered in an umbrella-shaped head.

Reproduction: 

• Poison hemlock reproduces by seed. 
• A single plant can produce 40,000 seeds that will remian viable for up to 6 years. 
• Seeds are easily transported by machinery, animals, water movement and humans. 

Habitat & Ecology

• Thrives in moist soils in sunny locations. 
• Commonly found along ditches, road sides, fields and disturbed areas. 

Impacts

Social: 

Poison-hemlock is toxic and all parts of the plant are poisonous. Poses as a risk to both people and animals. If you suspect someone has eaten poison hemlock, call the BC Poison Control Centre immediately (1-800-567-8911). 

• Dead canes can remain toxic for up to 3 years. 
• Can cause severe skin irritation and issues to the respiratory system. 
• Out completes native forage species and will be hazardous to livestock. 
• Often confused with edible plants in the carrot family. 

Management

When performing any control treatment to poison hemlock, minimize skin exposure; wear gloves, safety glasses and long sleeves. Wash hands, tools and clothes thoroughly after handling poison hemlock. 

Mechanical/Manual Control: 

• For small infestations hand pulling or digging up the plants is effective. Be sure to remove the entire root system. 
• If plant roots are too large to remove cut at least 3 cm below ground. 
• Manual removal is best done prior to flowering to reduce seeds being left on site. 
• Use and apply a layer of mulch to suppress new growth after removing plants. 
• Mowing is not recommended as this can lead to respiratory problems by breathing in the toxins. 
• Do not compost this plant. Place removed plant fragments in a bag for disposal. 

Resources

For further details on Poison Hemlock control please refer to the Metro Vancouver Best Management Practices for Poison Hemlock (pg. 12-21)

Download the Capital Region Invasive Species Program's Alert Sheet on Poison Hemlock here. 

Download A Guide to Weeds in British Columbia for Poison Hemlock here.

Sometimes confused with giant hogweed. Please check out Maine's Department of Agriculture, Conservation and Forestry's resource guide comparing look-alike species here. 

Download the Metro Vancouver Factsheet on Poison Hemlock here.

Download the King County Noxious Weed Alert's Factsheet on Poison Hemlock here. Please note this a US resource and Canadian guidelines and regulations may differ. Be sure to carefully read all labels before use. 

Header photo (Françoise Caclin).