-
Western water hemlock. Photo Credit: (c) Gerald D. Carr, courtesy of OregonFlora -
Western water hemlock flowers. Photo Credit: (c) Bruce N. Newhouse, courtesy of OregonFlora -
Western water hemlock flowers. Photo Credit: (c) Gerald D. Carr, courtesy of OregonFlora -
Western water hemlock. Photo Credit: (c) Gerald D. Carr, courtesy of OregonFlora -
Western water hemlock leaves. Photo Credit: Mary Ellen (Mel) Harte, Bugwood.org -
Leaf comparison of poison hemlock (right) and water hemlock (left). Photo Credit: Steve Dewey, Utah State University, Bugwood.org
NOTE: Western water hemlock is native to Oregon but it can be problematic in certain settings due to its toxicity to people and livestock.
Also known as: water hemlock, spotted water hemlock, spotted parsley
Western water hemlock is one of the most toxic plants that grows in North America. Only a small amount of the toxic sap it produces is needed to poison humans or livestock.
Description:
| Life Cycle: | Perennial (life cycle lasts more than one year) |
| Early Detection and Rapid Response species: | No |
| Height: | Up to 6 feet (2 meters) tall |
| Leaf Description: | Leaves are made up of several lance-shaped leaflets with serratedSerrated Having a jagged edge. edges. Its leaves grow alternately along the stems. Its roots and stems contain a highly poisonous sap that is toxic to humans and livestock if consumed. |
| Fruit & Flower Description: | Small, white flowers grow in umbrella shaped clusters. Each flower has five petals. After flowers mature, they are replaced by a small, brown fruit that contains a pair of seeds. |
| Bloom Time: | June to August |
Habitat:
- Water hemlock thrives in full to part sun but must have wet soils to grow.
- It is commonly found in wet places such as along stream banks, wetlands, ditches, and ponds.
Impact:
- Water hemlock’s roots and stems contain highly toxic liquid that is poisonous to people and livestock.
- It is particularly a concern in locations where accidental consumption may occur such as near schools, public parks, or where livestock graze.
What you can do about it:
- Always remember to protect yourself from water hemlock by wearing long sleeves, pants, and gloves.
- Small patches can be controlled by hand pulling or digging. Make sure to remove as much of the root as possible since new plants can grow from fragmented roots.
- Place all plant material in a tied plastic bag and dispose of in the garbage – not your yard debris bin or home compost.
- Mowing and tilling can effectively control larger infestations. Mowing or tilling should occur before plants have produced flowers and repeated in late summer.
Look-alikes:
Poison hemlock (Conium maculatum), another toxic plant, is often confused with water hemlock. Both plants have small, white, umbrella shaped flowers, but poison hemlock’s leaves are more complex and fern-like.
Noxious Weed Listing:
| State of Oregon: | Not listed |
| State of Washington: | Not listed |
More Resources:
Download Western Water Hemlock Best Management Practices factsheet
- Pacific Northwest Weed Management Handbook: Western water hemlock