Poison Hemlock is also known as:
- Deadly hemlock
- Poison parsley
- Poison fool’s parsley
General: Poison Hemlock is a biennial plant that forms a short leafy rosette in the first year, and develops a tall hollow stem and several clusters of flowers the following season.
Flowers: Are small, white, and grow into umbrella-shaped clusters (umbels) that are about 7 – 8 cm across, starting in early summer.
Stems: Are hollow, thick, hairless and ridged with purple spots. They are extensively branching and grow 0.5 – 3 m tall.
Leaves: Are triangular, shiny green and finely divided, giving them a fern-like appearance. Leaves are 3 to 4 times pinnately compound, and emit an unpleasant, parsnip-like odour when crushed.
Fruit: Are ridged and flattened, 2 – 2.5 mm long, with two seeds borne together.
Roots: Poison Hemlock has a long, thick, pale yellow or white taproot.
Invasive: Queen Ann’s Lace, or Wild Carrot (Daucus carota) is sometimes mistaken for Poison Hemlock, but this plant has one densely-packed, umbrella-shaped flower cluster on a narrow, hairy stem. Wild Carrot also flowers later in the summer.
Native: Water Hemlock (Cicuta maculata) is also similar to Poison Hemlock, but the leaf veins end in notches between the teeth of the leaflets, whereas in Poison Hemlock they end at the tips of the teeth.
Habitat and Origin
Poison Hemlock originates from Europe, and was introduced in North America as a garden ornamental.
Poison Hemlock thrives in wet ditches and moist disturbed sites, but it can also withstand dry soils. It is often found near roadsides, field borders, hiking trails, railroad tracks, stream banks, irrigation ditches, waste areas, riparian woodlands and open floodplains.
Propagation & Vectors of Spread
This plant spreads by seed. Poison Hemlock is a biennial plant; it forms a short, leafy rosette the first year, and develops a tall hollow stem and several clusters of flowers the following season.
One plant can produce over 1000 seeds, which remain viable in the soil for 3 – 5 years, leading to the rapid formation of a seed bank.
Poison Hemlock seeds are spread by machinery, on clothing, or in transported soil. They are also dispersed to a lesser extent by water and wind.
Ecological, Economic, & Health Impacts
- POISON. The volatile, oily compounds found in every part of the plant (especially the fresh leaves and fruit) are so poisonous that a few drops can kill a small animal.
- Human deaths have occurred from harvesting and consuming the roots, having been mistaken for wild carrots or parsnips. Lesser exposures cause skin irritation.
- For animals, symptoms include nervous trembling, salivation, lack of coordination, pupil dilation, rapid weak pulse, respiratory paralysis, coma and sometimes death.
- Reduces biodiversity; acts as a pioneer species, quickly colonizing disturbed sites and displacing native species.
What Can I Do?
Poison Hemlock is not yet found in the Sea to Sky Corridor, so the best approach to controlling its spread is by PREVENTION.
Learn to identify Poison Hemlock: use the images presented in this profile page to learn how to identify Poison Hemlock.
What to do if you spot it: You can report any Poison Hemlock sighting by clicking here.
- Regularly monitor properties for weed infestations.
- Ensure soil, gravel, and fill material are uncontaminated before transport.
- Minimize soil disturbances (e.g. use grazing plans that prevent soil exposure from overgrazing), and use seed mixes with dense, early colonization to revegetate exposed soil and resist invasion.
- Maintain a strong population of native perennials to provide competition to any Poison Hemlock plants.
- Ensure all plant parts are bagged or covered to prevent spread during transport to designated disposal sites (e.g., landfill).
- Do not unload, park or store equipment or vehicles in infested areas; remove plant material from any equipment, vehicles or clothing used in such areas and wash equipment and vehicles at designated cleaning sites before leaving infested areas.
- Do not plant Poison Hemlock in a garden, no matter how well-contained its enclosure may seem.
- Do NOT compost! Instead, dispose of Poison Hemlock in the general/household waste stream at the landfill as the seeds will be able to persist the composting process.
- Do not move soil, gravel, or fill material that has been contaminated with Poison Hemlock.
- Please exercise extreme caution when working near Poison Hemlock. Minimize exposure by wearing gloves and taking frequent breaks when pulling or mowing large amounts of plants.
- Mowing or hand-pulling before seed set will eventually deplete the seed bank.
- Since Poison Hemlock tends to grow in wet areas, the use of herbicides may be restricted or impossible.
- Where possible, foliar applications at the rosette stage (before the plant flowers) of dicamba, 2,4-D, and glyphosate have been used for chemical control of Poison Hemlock.
- Herbicide treatment may need to be repeated for several years until the seed bank is depleted.
- We recommend that any herbicide application is carried out by a person holding a valid BC Pesticide Applicator Certificate. Before selecting and applying herbicides, you must review and follow herbicide labels and application rates; municipal, regional, provincial and federal laws and regulations; species-specific treatment recommendations, and site-specific goals and objectives.
No biocontrol agents are available in BC, but Agonopterix alstroemeriana (moth) was accidentally introduced into the US and feeds exclusively on Poison Hemlock. It is used as a biological control agent in Idaho, Oregon and Washington, but it is not found in BC.
Capital Regional District, Poison Hemlock Species Alert Sheet, https://www.crd.bc.ca/docs/default-source/es-watersheds-pdf/invasive-species/poison_hemlock__factsheet_v5.pdf?sfvrsn=5fc1afca_4#:~:text=Poison%20hemlock%20is%20a%20priority,from%20ingestion%20or%20skin%20contact
Coastal Invasive Species Committee, Poison Hemlock, http://www.coastalisc.com/priority-invasive-plants/poison-hemlock7
Creston Valley, Invasive Plant Species: Poison Hemlock, http://creston.ca/DocumentCenter/View/1064/Poison-Hemlock?bidId=
CTV News, Invasive Poison Hemlock A Growing Concern on Vancouver Island, https://vancouverisland.ctvnews.ca/invasive-poison-hemlock-a-growing-concern-on-vancouver-island-1.4502558
District of Saanich, Poison Hemlock Invasive Plant Alert, https://www.saanich.ca/assets/Community/Documents/poison-hemlock-alert-web.pdf
Electronic Atlas of the Flora of BC, Conium maculatum, http://linnet.geog.ubc.ca/Atlas/Atlas.aspx?sciname=Conium%20maculatum
Government of BC, “Poison Hemlock” in A Guide to Weeds in British Columbia, https://www2.gov.bc.ca/assets/gov/environment/plants-animals-and-ecosystems/invasive-species/alerts/poison_hemlock.pdf
Invasive Plant Atlas of the United States, https://www.invasiveplantatlas.org/subject.html?sub=4365
King County Noxious Weeds Program, Poison Hemlock Identification and Control, https://www.kingcounty.gov/services/environment/animals-and-plants/noxious-weeds/weed-identification/poison-hemlock.aspx
Lillooet Regional Invasive Species Society, Poison Hemlock (Conium maculatum), https://lriss.ca/species/poison-hemlock-conium-maculatum
Southern Indiana Cooperative Weed Management Area, Poison Hemlock, https://www.extension.purdue.edu/extmedia/FNR/FNR-437-W.pdf
USDA Forest Service, Weed of the Week: Poison Hemlock, https://www.invasive.org/weedcd/pdfs/wow/poison-hemlock.pdf