Western waterhemlock begins growth in the spring. The tall, branching plants reach three to seven feet high by late spring to early summer, when flowering begins. The hollow, erect stems are swollen at the base and into the roots. The swollen, finger-like roots are typically divided into chambers by horizontal walls. Long-stemmed leaves are alternate on the branches, and are typically divided into several slender, pointed leaflets. Each leaflet is toothed, with the veins ending in the bottoms of the serrations instead of at the tips. This characteristic differentiates waterhemlock from other plants in the carrot family. Tiny white flowers occur at the tips of the branches in rounded, stalked, umbrella-shaped clusters. SPECIAL INFORMATION: This plant is extremely poisonous (particularly the taproot) and should be handled with caution, as there is no known treatment. The horizontally-chambered taproot is a distinctive feature of the species but may not be as apparent in young plants.

Habitat

Western waterhemlock grows in moist areas (along streams and ditches, in marshy areas, wet fields, etc.). It is considered one of the most poisonous plants in North America.

Management Options

Non-Chemical Management

None recommended

Select non-chemical management options as your first choice!

Chemical Management

IMPORTANT: Visit Home and Garden Fact Sheets for more information on using pesticides

None recommended; not a problem in healthy established turf. NOTE: Some ingredients listed here are only available in combination. Read the label carefully on combination products to make sure the product is suitable for your specific situation.

Landscape areas

Turf areas

2,4-D + MCPP + dicamba

Bare ground areas

Images

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Caption: Western waterhemlock flower clusters Photo by: R. Parker
Caption: Western waterhemlock leaves Photo by: R. Parker
Caption: Western waterhemlock root cross-section Photo by: R. Parker
Caption: Western waterhemlock flowers and leaves Photo by: N.R. Ness

WSU Extension

Hortsense