Poison hemlock

A feathery-leafed plant that’s spreading across Pennsylvania isn’t a wildflower but a poisonous weed that can kill.

A feathery-leafed plant that’s spreading across Pennsylvania isn’t a wildflower but a poisonous weed that can kill.

Poison hemlock reportedly killed the Greek philosopher Socrates in 399 BC. Today, you can find it along roads and streams.

Here a guide to poison hemlock from Penn State Extension and the U.S. Department of Agriculture

What is poison hemlock?

Poison hemlock (Conium maculatum) is a plant in the parsley family. The plant is native to Europe and parts of Africa. It was introduced to North America as an ornamental garden plant.

Why is this plant a big deal?

The plant is extremely poisonous to people and very toxic to sheep, cattle, swine, horses and other animals. All parts of poison hemlock, including the leaves, stem, fruit and root, are poisonous. Poisoning can cause muscle paralysis and skin irritation. Whistles made from hollow stems of the plant have caused death in children.

Are all hemlocks poisonous?

There are several types of plants called hemlock. Not all are poisonous. The Eastern hemlock tree (Tsuga Canadensis), for example is the state tree of Pennsylvania. The wood from these trees was used to build cabins. Bark was harvested for tanneries. And seeds in the cones of hemlock trees are a treat for birds such as grosbeaks, titmice, juncos and goldfinches.

How do I spot the poisonous kind of hemlock?

Look for red or purple spots on the stems at the low-growing stage. The spots grow larger in the second year and can make the stem look purple. The stems of poison are smooth and the plant grows 3-6 feet tall in its second year.

Poison hemlock has a musty smell and the leaves often have a parsley smell when crushed.

Wild carrot/Queen Anne's lace looks similar to poison hemlock but the stems are covered with dense hair. Wild carrot rarely grows more than two feet tall.

Contact the Lancaster County extension office at 717-394-6851 or LancasterExt@psu.edu for help identifying plants.

This video shows the difference between the two plants. 

Is this a new problem in Pennsylvania?

The weed has been more abundant in the past decade and growing through new regions throughout the state. 

It can be found growing in areas such as fence rows, roadsides, field edges and creek sides.

What is the plant’s life cycle?

Hemlock is a biennial plant, which means it takes two years to flower and go to seed. In the first year, the plant grows as a rosette, a low cluster of leaves. The plant may stay green through much of the winter. In early spring of he the second year, the rosettes grow. In late May, the plant grows to 3-6 feet tall with small white flowers from June through August. After flowering, the plant scatter new seed, die and the seeds will germinate to create new plants.

How do I remove this plant?

When removing the plant, wear gloves and protective clothing to avoid skin irritation. Dig up individual plants with shovel. The most effective way to remove poison hemlock is to treat the rosettes before the larger plant grows. Throw away the plants in the trash, not a compost bin.

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