Managing Poison Hemlock

Poison hemlock has been found in nearly every U.S. state and across much of Canada. This plant is highly toxic. In fact, ingesting even small amounts of the plant tissue can be poisonous to people and animals. Touching any part can cause a severe skin reaction. Contact with or inhalation of plant debris can also cause respiratory distress. Given the dangers of coming into contact with this plant, property owners should take care when managing poison hemlock.

Identifying Poison Hemlock


poison hemlock first growing season
During the first year of growth, poison hemlock is a low-growing and unobtrusive plant.

In its first year, poison hemlock is an unnoticeable, low-growing leafy rosette. After its second winter, the plant grows rapidly. Lacy foliage is pinnately compound, showing opposite arrangement on the stem. Smooth, hollow stems are green with easily observable purple spots. These spots are an important identifier and differentiate the plant from the closely related Queen Anne’s lace and wild carrot. Stems continue to grow upright and can reach eight to ten feet tall. White to yellow flower clusters appear in summer.

poison hemlock upright stems with purple spots
Purple spots on the upright stems are a hallmark of established poison hemlock plants.

Look for this plant in shaded habitats, near rivers and streams, and in lowland areas or ditches. It often grows mixed with other vegetation, making it more difficult to spot.


A single plant produces tens of thousands of seeds meaning the plant spreads rapidly. Since it so toxic and prolific, managing poison hemlock can be tricky. Hand removal, digging, cutting and burning pose health risks. Further, these methods disturb the soil, causing germination of any remaining hemlock seeds that will subsequently begin growing.

Targeted and careful herbicide applications can help best control poison hemlock. This is especially true when you consider the hazards other tactics pose. Though these treatments can be applied at different points in the plant lifecycle, they are most successful during the first growing season. Therefore, early identification is important. Certainly, use of herbicides is still an option once vertical growth or flowering has begun.

If you observe poison hemlock, treat it with great caution and quickly take action to recue the spread.

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