How to Identify Poison Hemlock—and Get Rid of It Safely

In late spring and early summer, you may spot a tall plant with lacy, white, umbrella-shaped flowers blooming along roadsides, in fields, or even in an overgrown corner of your yard. Is it a harmless wildflower—or a deadly impostor?

Poison hemlock (Conium maculatum) is a toxic invasive plant found throughout the United States. Even a small amount can be fatal if ingested. It’s essential to know how to identify it, especially because it can look similar to plants people may forage, as well as where it grows and what experts say about removing it safely.

Native to Europe, northern Africa, and western Asia, poison hemlock was introduced to the United States as an ornamental plant in the 1800s. It has since spread widely. All parts of the plant—including the leaves, stems, roots, and fruit—are toxic if eaten, and skin irritation may occur after contact.

“Poison hemlock contains alkaloids which cause respiratory distress if ingested,” says Pamela Bennett, a professor and master gardener program director at Ohio State University. “It’s a huge problem for livestock, such as sheep and cows, who may graze it in a pasture. A small amount is fatal for livestock.”

This plant is a biennial, meaning it takes two years to mature. In its first year, it grows as a low rosette, making it difficult to notice.

“But people notice it the second year because it shoots up a stalk 8 or more feet tall, producing white umbrella-shaped flowers and numerous seeds, so it keeps coming back and spreading,” says Bennett.

Where Does Poison Hemlock Grow?

Poison hemlock prefers moist soils but can be found almost anywhere. It adapts to a variety of conditions, especially areas of disturbed soil. It’s typically found on roadsides, in ditches, on the edges of cultivated land, along creeks, and in agricultural fields. But it also can be found in landscape beds in your yard if the seeds have blown into them.

Interestingly, pollinators such as bees, wasps, flies, moths, and butterflies do visit this plant. In fact, it is a host plant for the black swallowtail butterfly. The fruits also may be eaten by waterbirds.

How to Identify Poison Hemlock: Look for Purple-Spotted Stems

It’s most commonly recognized in its second year when it blooms. Poison hemlock is in the carrot family, so it has fine fern-like foliage. It’s often said to have a musty odor. The flowers appear in late spring, and they have purplish spots on the stems. “That’s the identifying feature because several other plants resemble it, such as Queen Anne’s lace (Daucus carota), but they do not have the characteristic purple spots on the stems,” says Bennett.

Those purple spots on the stem are a telltale sign.

This plant also resembles giant hogweed (Heracleum mantegazzianum), which has white umbrella-like flowers, too. However, giant hogweed grows much taller, maxing out at 15 feet tall by early to midsummer. The danger of giant hogweed is that it contains furocoumarins in the sap, which can cause skin to be sensitive to UV light. Swelling and blisters may occur, with permanent scarring.

Poison hemlock is perhaps best known as the plant used in ancient Greece to execute the philosopher Socrates.

How to Get Rid of Poison Hemlock Safely

It’s easiest to destroy this invasive plant if you catch it the first year, says Bennett. Spray it with a broadleaf herbicide, such as glyphosate, 2,4-D +dicamba, or 2,4-D +triclopyr.

You can dig up individual plants, too, but make sure to get the entire taproot, which can go at least a foot down, says Bennett. Or cut it back, then spray it again. You will need to treat with herbicide until no more green foliage returns. Do not compost this plant; dispose of it in the trash.

Also, because it may cause skin irritation, always make sure to wear the proper protective clothing, such as long pants, long sleeves, and gloves if you are string trimming or weeding in an area where you suspect you have poison hemlock. Finally, never burn this plant, which may cause injury if you inhale the fumes.