Public Service Announcement: Poison Hemlock is in bloom! (2024)

Poison Hemlock flower cluster. (Photo by Marcus McCartney)

Right now one of our most toxic weeds in Washington County is in full bloom! Like clockwork this time of year, I have received numerous calls and emails on how to control this nuisance, yet deadly, plant.

Poison Hemlock is a noxious weed in Ohio, meaning this weed is regulated by Ohio State law and should be destroyed or eradicated if found on your property. All parts of this plant are poisonous to humans and livestock, so it is important to know how to identify and to properly remove and destroy it. Poison Hemlock is a biennial, meaning it completes its life span in two years. During the first year (vegetative growth), leafy rosettes form extending upwards of two feet. During the second year (reproductive growth), the plant sends up its tall reproductive shoot (stem) with flowers.

It Can Kill

Poison Hemlock is highly toxic to humans and livestock when ingested — either in its vegetative stage or when dried. As the tale goes, this plant was used to poison and execute the Greek philosopher Socrates after he was found guilty of corrupting the minds of young Athenians and for not believing in the gods of the state.

Typically, grazing animals will avoid poison hemlock because of its unpalatable taste, unless there is little other feed or forages available or when it’s consumed through hay.

Full Poison Hemlock plant. (Photo by Marcus McCartney)

Caution should be taken when handling the plant. The sap (juices) can cause toxic reactions in humans, resulting in a red irritating skin rash.

What does it look like

The first step to controlling Poison Hemlock is being able to recognize the plant. Right now, is a great time to identify the plant, because currently it is somewhere between 2 to 5 feet — with the potential to reach heights of 10 to 12 feet in moist conditions.

The leaves are dark glossy green, fern-like, triangular, and 3-4 times pinnately compound. Probably the most identifiable characteristic is the plant’s smooth hairless purple-spotted stem. The stem is also hollow between the nodes (where the leaves attach to the stem). The plant’s flowers are small, white, and found in umbel-shaped clusters. Do not confuse Poison Hemlock with wild carrot (aka: Queen Anne’s Lace) as the leaves and flowers look similar.

How To Control Poison Hemlock

Purple spotted Poison Hemlock stem. (Photo by Marcus McCartney)

Poison Hemlock can be controlled quite easily, either mechanically (organic) or chemically.

Mechanical Control: Since poison hemlock is a biennial, it wants to die after flower pollination, therefore the plant does not store any reserve energy in its roots for later use. It takes up to six weeks for the seeds to become viable once the flowers are pollinated. About a week after the plant has flowered, while wearing gloves simply chop it down at the base. No regrowth will occur at this time because there are not any plant reserves in its roots. Once cut, you can discard it over a hill away from humans and livestock or throw it in the trash. Do not burn it!

This will end seed production. Of course, if this plant has been present on your property for a while, it may take you up to three to five years to completely eradicate and exhaust the soil’s seed bank. Poison Hemlock seeds are only viable for that long.

Chemical Control: According to the Ohio State University Weed Control Guide, Crossbow and Remedy Ultra has the best rating for controlling Poison Hemlock, followed by glyphosate (Roundup), dicamba, and Cimarron Max. The plant can be sprayed anytime, but best results occur when the plant is small. Remember when applying chemicals, the applicator should wear proper PPE (personal protective equipment) and follow the label accordingly.

If you think you have Poison Hemlock on your property and need help identifying it, please call the OSU Extension office for assistance: 740-376-7431.

Leaf of a Poison Hemlock plant. (Photo by Marcus McCartney)

Marcus McCartney is the OSU Extension Agriculture and Natural Resources Educator for Washington County. He has been with Extension since 2014. Marcus received both his bachelor’s and master’s degrees from West Virginia University.