One of the 'deadliest plants in North America' is blooming. What to know about poison hemlock

GALION, Ohio – Poison hemlock, a dangerous weed that has only been in the Buckeye State for a few years, is in full bloom this week in North Central Ohio.

The hazardous plant is more visible in the area this year than ever before, according to Jason Hartschuh, Ohio State University Extension agent for Crawford County.

"It’s everywhere. You about can't drive U.S. 30 and not see it," Hartschuh said. "It keeps spreading by wildlife and by water and flood plains."

Poison hemlock started making news in 2019 when it was reported to have spread across southern Ohio. Now it's abundant across the state. The plant is also prevalent in Pennsylvania.

Dangerous if eaten

The plant can be deadly if eaten, said professors Joe Boggs and Erik Draper, in The Ohio State University's Buckeye Yard & Garden online blog.

"Poison hemlock is one of the deadliest plants in North America," they wrote. "Plants contain highly toxic piperidine alkaloid compounds, including coniine and gamma-Coniceine, which cause respiratory failure and death in mammals. The roots are more toxic than the leaves and stems; however, all parts of the plant including the seeds should be considered dangerous."

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The plant is in the carrot family, as is Queen Anne's Lace, and their similarities can make them hard to differentiate.

"The roots of wild carrot, or Queen Anne's lace (Daucus carota), are sometimes eaten raw or cooked," the professors wrote. "Unfortunately, they bear a striking resemblance to poison hemlock roots and misidentifications have been responsible for a number of accidental poisonings."

Not safe for animals, either

Farmers who have pasture land will want to keep an eye out for poison hemlock to ensure none of it is growing where their animals are grazing.

"Most of the time livestock are smart enough to not eat it," Hartschuh said. "Where we get into trouble is if we get a drought and everything else goes dormant and that's the only thing still green, they'll eat it."

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Hayfields are also at risk of becoming invaded by poison hemlock, and animals can still become sick if some of the plants make it into their bales of hay.

"It does lose some of its toxicity when it dries," Hartschuh said. "But it does still have toxins when it's dry."

Positive identifications increasing

Like parsley and other carrot family members, poison hemlock will have tiny white flowers that grow in clusters this time of year.

A big difference in the plants is that the stalk of poison hemlock is purple, according to Josh Dyer, director of the Crawford Park District.

"It’s a dead giveaway," Dyer said. "The other ones are typically green."

From a distance, though, the various related plants can be hard to distinguish.

"There are a few different species out there that look similar," Dyer said.

That resemblance made most sightings in years past false alarms. But as poison hemlock has taken hold in North Central Ohio, most calls the naturalist has received have led to positive identifications.

"It's really taken off," Dyer said. "I don't know if it's wind or water-driven, but it seems like it likes being near water."

Flowers only in its second year

Poison hemlock is a biennial, meaning it takes two years to complete its biological lifecycle. The plant is hard to identify during its first year.

"It flowers on the second year," Hartschuh said. "The first year it's a small rosette six to eight inches tall. The second year, it bolts and that's when it can get six feet tall."

Fortunately for those attempting to control its population, the plant dies after the second year – propagation can only happen through the plant's seeds, not via its root system.

"Things that are a biennial can be controlled much better than things that are perennials," Dyer said. "You just have to be diligent and knock it back."

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Painful skin irritant

But hacking away at poison hemlock can be a very painful task if the proper precautions are not taken.

"It can cause blisters," Hartschuh said. "If you're out weed eating, you should wear splash-proof goggles and maybe a face shield because you don't want that juice getting on your lips or in your eyes."

If the plant has already started to flower, then cutting the heads off and placing them inside a plastic bag to be thrown away will help reduce the spread of seeds.

One of Dyer's colleagues recently tried to eradicate some poison hemlock and discovered the hard way how dangerous the plant really is.

"They got really bad blisters from it," Dyer said. "I assume it's like other irritants – it depends on the individual and how they respond to it."

Poison ivy is a good example he said. Some people are deathly allergic, while others only become mildly irritated.

His final advice was to leave the chopped plants in a pile, or take them to the landfill – just never torch them, regardless of the situation.

"I wouldn't burn it," Dyer said. "Like with poison ivy, if you burn it the oils will get in the air and you can get poison ivy in your lungs. I don't know yet if poison hemlock is the same, but I would not want to risk it."

Follow Zach Tuggle on Twitter: @zachtuggle

This article originally appeared on Mansfield News Journal: Poison hemlock, a deadly weed, is blooming across Ohio. How to spot it