Poison Hemlock

Poison hemlock is a biennial forb in the Apiaceae (carrot) family. It grows from a taproot to form a basal rosette in its first year of growth; in the second year of growth, it produces a stem that usually reaches 3 feet and occasionally up to 8 feet tall. Leaves are green in color and are large (up to 16 inches) but finely divided giving them a lacey or fern-like appearance. Leaf veins end at the tips of the “teeth”. Poison hemlock stems are green with purple spots; stems are hollow and glabrous. Poison hemlock produces showy clusters of white flowers from late spring to late summer. Individual flowers are small but produced in large umbles. Seeds are small and gray-brown with five long ridges. Roots are large, fleshy taproots that may be pale yellow in color.

Poison hemlock produces toxic alkaloids in all parts of the plant. These alkaloids are fatally toxic to humans, livestock, and wildlife if ingested. Care should be taken when handling all parts of the plant as the alkaloids are also phototoxic and can cause burns and blisters on exposed skin. If you suspect hemlock poisoning, contact Poison Control at poison.org or 1-800-222-1222 immediately.

Poison hemlock is native to Europe and was introduced to North America as an ornamental plant in the 1800s. It is a prolific seed producer. It is frequently found in disturbed sites and riparian areas.

Prevention and cultural control strategies should be utilized as much as possible.

There are no biological control agents available for poison hemlock at this time.

Hand pulling and digging out of the taproot can be effective. **Wear gloves and long sleeves when handling poison hemlock. Wash hands after handling** Mowing is not generally effective as the plant may regrow from the root stock. Grazing is not recommended for managing poison hemlock as it is toxic to livestock.

Dense infestations can be controlled with herbicides. Early summer treatments prior to flower are most effective, but treatment of rosettes will provide multiple years of management. Read the label before using any herbicide. Contact TCWP if you have any questions about application rates or how to use an herbicide.

This species is not actively managed through TCWP programs, but additional information on managing this species is available upon request.

• Field Guide for Managing Poison Hemlock in the Southwest (2015) United States Department of Agriculture Forest Service.
• Weed Report: Poison hemlock from Weed Control in Natural Areas in the Western United States (2013) DiTomaso, J.M., Kyser, G.B., et al. University of California Weed Research and Information Center.
• Poison hemlock identification and control. (2023) Anderson, E., Branstrom, I., and Hill, E., Michigan State University Extension.
• Poison hemlock identification and control. King County Noxious Weed Control Board.
• Poison Hemlock (2022) Cleveland Clinic.