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Poison hemlock flowers. Photo Credit: Eric Coombs, ODA, Bugwood.org -
Poison hemlock flowers. Photo Credit: John Cardina, the Ohio State University, Bugwood.org -
Poison hemlock leaves. Photo Credit: Ansel Oommen, Bugwood.org -
Poison hemlock leaves. Photo Credit: John Cardina, the Ohio State University, Bugwood.org -
Leaf comparison of poison hemlock (right) and water hemlock (left). Photo Credit: Steve Dewey, Utah State University, Bugwood.org
Also known as: poison parsley, spotted hemlock, carrot-fern
Poison hemlock is considered one of the most poisonous plants in North America. The entire plant is toxic to people and livestock. Once established, it can spread quickly across pastures and along waterways.
For a more detailed description, download the Poison Hemlock Best Management Practices factsheet.
Description:
| Life Cycle: | Biennial (life cycle lasts two years) |
| Early Detection and Rapid Response species: | No |
| Height: | Up to 8 feet (2.4 meters) tall |
| Leaf Description: | The leaves are compoundCompound A leaf consisting of several distinct leaflets joined to a single stem. and grow alternate along the stem. Its fern-like leaves are light green. Leaves emit an unpleasant smell when brushed against or crushed. |
| Fruit & Flower Description: | Small, white flowers grow in umbrella shaped clusters. Flower clusters grow at the end of the plant’s upright stems. Small seeds are brown and barrel shaped. It exclusively spreads by seed. A single plant can produce 30,000 seeds annually. Seeds can remain viable for six years. |
| Bloom Time: | June to August |
How it spreads:
- Poison hemlock reproduces exclusively by seed.
- Seeds fall near the plant but can also be dispersed by boots, clothing, animal fur, birds, water, and wind.
Habitat:
- Prefers areas with full sun and moist soil, but is adaptable to other conditions.
- It is commonly found in grasslands, pastures, as well as along streams and freshwater wetlands.
Impact:
- Poison hemlock is lethal when ingested. It’s roots and flowers are especially toxic.
- It can quickly spread across pastures and riparian areasRiparian Areas Areas of land that occur along the edges of rivers, streams, lakes, and other bodies of water., reducing forage, poising livestock, degrading habitat, and outcompeting other plants.
What you can do about it:
- Always remember to protect yourself from poison hemlock by wearing long sleeves, pants, and gloves.
- Manual: Hand pulling or digging can control small patches.
- Place all plant material in a tied plastic bag and dispose of in the garbage – not yard debris or home compost.
- Mowing and tilling are effective controls for larger infestations. Mowing in the spring and late summer before and after plants have produced flowers will provide better results. Several years of mowing will be needed.
Look-alikes:
Western water hemlock (Cicuta douglasii), another toxic plant, is often confused with poison hemlock. Both plants have small, white, umbrella shaped flowers, but water hemlock’s leaves are less incised and not as fern-like.
Noxious Weed Listing:
| State of Oregon: | Class B |
| State of Washington: | Class B |
More Resources:
- Pacific Northwest Weed Management Handbook: Poison hemlock
- University of California, Weed Research & Information Center: Poison hemlock