Deadly poison hemlock is in full bloom across Pennsylvania

Written by on July 13, 2021

Deadly poison hemlock is in full bloom across Pennsylvania

By Megan Frank

July 13, 2021

Poison Hemlock. Image by JackieLou DL from Pixabay 

One of America’s deadliest plants is in full bloom across Pennsylvania.

Listen to the story.

Poison hemlock is infamously known as the plant that killed Greek philosopher Socrates and now, it’s being spotted along roadsides and in backyards in the commonwealth. 

While it’s a pretty weed, its looks are deceiving. Amy Faivre is a professor of biological sciences at Cedar Crest College. She says poison hemlock has a musty odor and produces tiny white flowers that form umbrella-like clusters. 

“Ironically, it was introduced to be a garden plant. It has the same kind of inflorescence that Queen Anne’s lace does, only bigger,” says Faivre.

Poison hemlock stalks can grow 6-10 feet high, and Faivre says just brushing up against it can cause skin irritation. 


“Some people from touching it can get dermatitis, a rash. But the biggest issue is to make sure that people don’t touch it and eat it,” says Faivre. “The other piece is of course livestock. It’s toxic to mammals.”

According to the United States Department of Agriculture (USDA), all parts of poison hemlock — leaves, stem, fruit, and root — are poisonous. Faivre says people who remove it should wear protective clothing, including gloves and a face mask.

“The entire plant is toxic,” says Faivre. “If you’re going to remove it, think of it like poison ivy. You can dig it out, but it does have a pretty good taproot.”

Faivre says it can take 3-6 years to completely remove poison hemlock from a property.

PennState Extension also reports that poison hemlock is spreading aggressively across Pennsylvania. Faivre says people may be noticing the plant more too due to increased time spent outdoors during the pandemic. 

“It’s quite possible that it’s spreading, but it’s also possible that people suddenly noticed it a lot last year when they had more time on their hands to go out for walks,” says Faivre.

Faivre says poison hemlock roots can be mistaken for wild parsnips, and the leaves can be mistaken for parsley, which is the main reason for accidental poisoning. 

“The highest level of toxicity has been recorded in the seeds, but there’s also quite a few toxins in the roots,” says Faivre. “People do sometimes harvest the root of poison hemlock, confusing it with other plants that you could eat the root of, and so people have died by eating the root.”

The USDA says a person with hemlock poisoning may experience a rash, tremors and may salivate and should be taken to the hospital right away. Early treatment may prevent paralysis, suffocation and death. 

The plant flowers from mid-June to early August. Click here for tips to identify poison hemlock and its look-alikes. 

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