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Noxious weeds

King County, Washington

To offer a suggestion or report an error on the King County Noxious Weeds website, please contact Sasha Shaw, education specialist.

Poison-hemlock flowering - click for larger image Poison-hemlock
Conium maculatum

Poison-hemlock is acutely toxic to people and animals. In western Washington, it is common on roadsides, in open fields, and in natural areas. Unrelated to the native evergreen hemlock tree, poison-hemlock can be deadly; it has gained notoriety through its use in the state execution of Socrates.

Poison-hemlock can be confused with wild carrot (Daucus carota, or Queen Anne's Lace), as with many other members of the parsley family that resemble it. It has hairless hollow stalks with purple blotches. It can get quite tall, sometimes up to 8 feet or higher. It produces many umbrella-shaped flower clusters in an open and branching inflorescense. In contrast, wild carrot has one dense flower cluster on a narrow, hairy stem, usually with one purple flower in the center of the flower cluster, and is usually 3 feet tall or less. Poison-hemlock starts growing in the spring time, producing flowers in late spring, while wild carrot produces flowers later in the summer.

Toxicity

Poison-hemlock flowering - click for larger imagePoison-hemlock is acutely toxic to people and animals, with symptoms appearing 20 minutes to three hours after ingestion.  All parts of the plant are poisonous and even the dead canes remain toxic for up to three years.  The amount of toxin varies and tends to be higher in sunny areas.  Eating the plant is the main danger, but it is also toxic to the skin and respiratory system.  When digging or mowing large amounts of poison-hemlock, it is best to wear gloves and a mask or take frequent breaks to avoid becoming ill.  One individual had a severe reaction after pulling plants on a hot day because the toxins were absorbed into her skin.  The typical symptoms for humans include dilation of the pupils, dizziness, and trembling followed by slowing of the heartbeat, paralysis of the central nervous system, muscle paralysis, and death due to respiratory failure.  For animals, symptoms include nervous trembling, salivation, lack of coordination, pupil dilation, rapid weak pulse, respiratory paralysis, coma, and sometimes death.  For both people and animals, quick treatment can reverse the harm and typically there aren’t noticeable aftereffects. If you suspect poisoning from this plant, call for help immediately because the toxins are fast-acting – for people, call poison-control at 1-800-222-1222 or for animals, call your veterinarian.

Legal status in King County, Washington

Poison-hemlock leaves - click for larger imageThis widespread Class B weed is found throughout Washington. It is on the Non-Regulated Noxious Weed List for King County, Washington. Control of poison-hemlock in King County is recommended but not required. Poison-hemlock is not on the prohibited plants list administered by the Washington State Department of Agriculture, but some nurseries have volunteered to stop selling it due to its danger to natural resources. Some counties in Washington do require control of poison-hemlock so contact your local county weed board for rules in your area if you are outside of King County.

The King County Noxious Weed Control Board encourages property owners to remove poison-hemlock where possible and to avoid introducing it to new landscapes. Information on identification and control can be found in Poison-hemlock Weed Alert (144 kb, Acrobat file).

Apoison-hemlock flowers - click for larger imagedditional information on poison-hemlock

What to do if you find this plant in King County, Washington

Because poison-hemlock is so widespread, property owners in King County are not required to control it and we are not generally tracking infestations. We can provide advice on how to control poison-hemlock, but there is no legal requirement to do so. If you notice this plant near where people are growing or collecting food, we recommend that you remove it if it is on your property or if it is on public property that you contact the agency in charge. This is especially important in p-patch or community gardens where new gardeners or newcomers to our area may be unfamiliar with this plant.  In public parks or on trails, you can contact the local parks department and encourage them to remove the plants where they are most accessible to people who might be harvesting wild plants for food.  If you are unsure about who to contact, we can help (email us). 

Poison-hemlock photos - click thumbnail to see larger image

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poison-hemlock click for larger photo poison-hemlock click for larger photo Young poison hemlock plant - click for larger image poison-hemlock click for larger photo  ppoison-hemlock - click for larger image

Related information

Related agencies


Program offices are located at 201 S. Jackson St., Suite 600, Seattle, WA 98104. To contact staff, see the Noxious Weed Control Program Directory, send an email, or call 206-477-WEED (206-477-9333).