Poison hemlock and wild parsnip: How to identify and remove the invasive plants

Neither poison hemlock nor wild parsnips are native to Ohio, but both of the invasive species are here to stay and can be dangerous if you encounter or ingest them.

The plants thrive in continuously wet conditions, according to the Ohio State University's Buckeye Yard & Garden Online blog, and where there's one, there may be the other. Poison hemlock and wild parsnips are often found growing together.

If you come across one or both of the plants in your yard or outdoors this season, here's what you need to know.

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What does poison hemlock look like?

Poison hemlock is a recognizable plant, as its stems are ribbed and hollow with "purplish streaks or splotches," according to the National Parks Service.

The poisonous plant, which resembles Queen Anne’s lace or wild fennel, has been making its way all over the state, including Southwest Ohio and the Cincinnati region, in the last 20 years. It can be found all over, such as along roadways, parking lots and other areas with disturbed soil. 

Poison hemlock is biennial, meaning it takes two years to complete a life cycle, and can grow 2 to 10 feet tall. It can be found in nearly every contiguous U.S. state including Ohio, according to the National Parks Service. 

Joe Boggs, an assistant professor, commercial horticulture educator and co-leader at OSU Extension's Buckeye Environmental Horticulture Team previously told The Enquirer poison hemlock started by being planted as an ornamental decoration in the eastern U.S. around the late 1800's, but did not experience explosive growth until more recently.

At this point, Boggs said poison hemlock is too widespread to eradicate it, but education and awareness on the plant is the next best step.

What happens if you eat poison hemlock?

The invasive species is, as its name suggests, deadly if any part of the plant is ingested, from the seeds, stems, leaves or roots.

The main concern for poison hemlock ingestion is more with humans than animals, but it could pose a potential problem if pets like dogs or cats eat the plant.

All parts of this plant contain toxic alkaloids that can be fatal if ingested in any amount. According to Healthline, the alkaloids in poison hemlock can affect nerve impulse transmission to muscles, which eventually can kill the person through respiratory failure. There is no known antidote.

While the seeds germinate in the fall, poison hemlock does not usually produce flowers until the second spring. 

It is able to spread by reproducing seeds that mainly fall between September to December, which are dispersed via fur, birds, water and wind, to a limited extent. Seeds can also fall as late as the end of February. 

What does wild parsnip look like?

Parsnips have been cultivated as a root crop in Europe for centuries, but wild parsnip is much more dangerous to humans. Both parsnips and wild parsnips contain a plant defense chemical called psoralen in the sap, but wild parsnips contain much higher concentrations to defend against herbivores.

Wild parsnips usually follow a biennial life cycle, and most commonly germinate in the spring, according to OSU's Buckeye Yard & Garden Online blog. The plant spends its first year in a vegetative state as a low-growing basal rosette, which produces a robust root system.

By the second year, plants bolt during the reproductive stage to produce a single, thick, deeply grooved, greenish-yellow stem. Wild parsnip plants die after producing seeds.

Mature wild parsnip weeds can grow to as tall as 8 feet, although most only grow to 5-6 feet.

What happens if you touch wild parsnip?

Contact with the sap found on wild parsnip can cause the skin to blister painfully. Brushing up against the plant can cause sap to get onto human skin.

The sap invades the DNA of cells responsible for protecting you from the sun's ultraviolet radiation. If you go into the sun after exposure to the sap, the blisters will appear several days later.

When the affected skin is exposed to long-wave ultraviolet radiation, it can cause severe blistering, called phytophotodermatitis. These burn-like symptoms and other skin discolorations may last for several months.

How to safely remove poison hemlock and wild parsnip

Boggs previously told The Enquirer he recommends using "extreme caution" around both poison hemlock and wild parsnips. He advises to wear gloves, long-sleeved shirts and eye protection when handling or removing the plants.

Boggs also recommended to remove poison hemlock before it blooms and is able to produce seeds.

Wild parsnip, which is often found growing alongside poison hemlock, can react with the skin if touched, destroying epidermal cells and possibly leading to severe blistering.