Poison hemlock – What the home gardener needs to know

Source: Sharon Flynt, UK extension horticulture agent

      County extension offices around the state have fielded many phone calls this spring and summer from homeowners and gardeners concerned about poison hemlock. The concern seems to be justified but only if the poison hemlock is ingested by humans or livestock.

Poison hemlock is one of the most toxic plants in the world. It is well known throughout history for accidental deaths of humans and animals. One of the most well-known poison hemlock deaths took place in 329 B.C. when Greek philosopher Socrates ingested the deadly plant.

     Poison hemlock has been getting closer to populated areas recently and Kentucky isn’t immune. Poison hemlock is a biennial flowering plant, meaning it takes two years to complete its biological lifecycle. The first year the plant grows leaves, stems and roots. Low rosettes of parsley or fern-like shiny green, triangular leaves with a very pungent odor is noticeable. It will grow no taller than 2 to 3 feet the first year.

    The second year of the plant’s biennial season, plant growth completes with the formation of longer stems, flowers, fruit and seeds. It’s easy to confuse poison hemlock with Queen Ann’s Lace, which is in the carrot family and is not poisonous. In year two, the plant can grow from 2 to 10 feet tall, and the stems have purple splotches. The purple spots are what distinguishes it from other plants. Each plant can produce up to 40,000 seeds.

     Poison hemlock is usually found in unmaintained disturbed sites along fence rows, field edges, ditches, roadsides and low-lying areas with moist soil and shade. Disturbances, such as construction, utility work, or people working the land where poison hemlock is present, help to germinate the abundant seeds. Keeping the plant from going to seed is the best way to prevent spread. You can use preemergent and post herbicides to prevent or kill poison hemlock, but timing is key when applying.

    Contact (YOUR COUNTY) office of the University of Kentucky Cooperative Extension Service for information on poison hemlock.   

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