Poison-hemlock identification and control
Poison hemlock, a non-regulated Class B noxious weed, is a widespread toxic biennial often found in riparian areas, fields, vacant lots, and on roadsides. Eating even a small amount of any part of this plant can kill people, livestock, and wildlife. Stems are hairless, hollow, and ribbed, with reddish or purple spots and streaks. Leaves are fern-like and bright green, with a musty smell. In late spring, second-year plants reach 8-10 feet tall and produce numerous umbrella-shaped clusters of tiny, white, 5-petaled flowers.
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 reach up to 8 feet or higher. It produces many umbrella-shaped flower clusters in an open and branching inflorescence. 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.
Poison-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
This widespread Class B noxious weed is found throughout Washington. It is on the Non-Regulated Noxious Weed List for King County, Washington and control of poison-hemlock in King County is recommended but not required. For more information about noxious weed regulations and definitions, see Noxious weed lists and laws.
The King County Noxious Weed Control Board encourages property owners to remove poison-hemlock where possible and to avoid introducing it to new landscapes.
- Poison-hemlock Weed Alert (2.3 Mb, Acrobat file)
- Poison-hemlock alert posters translated into multiple languages (link)
- Washington State Noxious Weed Control Board (external link)
- Clark County, Washington Fact Sheet
- Cornell University Poison Plants Database (scroll down)
- Colorado State University Extension
- TNC Weeds Element Stewardship Abstract
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 in this county. If you notice poison-hemlock on public property where people are growing or collecting food, please notify the property manager or 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).