An herbaceous erect biennial, occasionally a winter annual. During the first year of growth, poison hemlock forms a large rosette and usually remains in the vegetative stage. It can easily grow to 7 feet on a rigid central stem that branches towards the top. Its stem is hollow except at the nodes, the points at which the leaf attaches. Leaves are clasping on a stout stalk and are deeply divided. Plants progress from a shiny deep green to a dull light green as they mature. Mature stems will exhibit red to purple splotches especially from ground to the mid-point. Closely clusters of white flowers at the branch ends near the top form an umbrella shape. All plant parts are extremely toxic! USE CAUTION WHEN HANDLING. A number of people are poisoned each year in North America some fatally.

Can be somewhat difficult to manage usually due to a large seed bank in the soil. Hand removal is possible but persistence is required. Poison hemlock remains toxic for several years after being pulled, especially the roots. Biocontrol agents are present and active. Poison hemlock is sensitive to most common herbicides, however the key to good control is early treatment, usually by early to mid-April. Planting and maintaining hardy perennial grasses usually prevent further encroachment.
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Information modified from “Selected Noxious Weeds of Eastern Oregon,” by Gary Page, Malheur County Weed Inspector.  Material for this feature is provided by Jordan Valley Cooperative Weed Area Coordinator Eric Morrison.