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  • Writer's pictureJohn Chapin

Beware of Poison Hemlock: What to Do if You Come Across This Toxic Plant


poison hemlock

This year, a noxious weed has appeared in extensive patches locally. Poison hemlock (Conium maculatum), native to Europe and Northern Africa, has unfortunately become widespread across North America, and is well-established in Indiana. I’m not sure why there haven’t been public warnings since it is highly toxic to people and animals. It’s toxicity primarily results from consumption, but poisoning can also result from inhalation or from skin contact.


Poison hemlock is a biennial member of the carrot family. First year plants look like carrot plants with bright green, fern-like leaves that have a strong musty odor when crushed, but with smooth stems and distinctive purple-reddish blotches. Second-year plants quickly grow 6-10 feet tall and produce billows of umbrella-shaped flower heads that look like Queen Anne’s Lace on steroids.


Poison hemlock is acutely toxic, with symptoms appearing 20 minutes to three hours after exposure or ingestion. All parts are poisonous and even the dead canes are toxic for up to three years. When controlling poison hemlock by pulling or mowing, wear gloves and long sleeves, mask up, and take frequent breaks. Severe reactions can occur, especially on hot days as toxins can be absorbed into skin.


Upon contact or exposure, symptoms for people include pupil dilation, dizziness, and trembling, followed by slower heartbeat, paralysis of the central nervous system and muscle paralysis. Death due to respiratory failure is a real possibility. For animals, symptoms include nervous trembling, salivation, lack of coordination, pupil dilation, rapid weak pulse, respiratory paralysis, coma, and sometimes death. Fortunately, for both

people and animals, quick treatment can reverse the harm and usually there aren’t any serious aftereffects. If you suspect poisoning from this plant, call 911 for help immediately because the toxins are fast-acting. If pets or livestock show symptoms, take to a veterinarian. Be careful!

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