Wild Flowers: Poison Hemlock

Updated on February 8, 2020
OldRoses profile image

Caren White is a Master Gardener and instructor at Home Gardeners School. She has been associated with Rutgers Gardens for over a decade.

This spring I noticed a strange plant growing along the edge of the woodland in my backyard. It looked a lot like Queen Anne’s Lace but much larger. Valerian perhaps? The woodlands in my backyard are part of a wetlands area and valerian likes wet places.

I did some research and discovered that what was growing in my backyard was poison hemlock (Conium maculatum), a Queen Anne’s Lace look-alike and relative.

Poison Hemlock growing in my backyard
Poison Hemlock growing in my backyard | Source

What is Poison Hemlock?

Poison hemlock is a member of the carrot family like Queen Anne's Lace but it is much larger, growing anywhere from 5 to 8 feet in height. It is originally from Europe and North Africa. European colonists brought it here as a garden plant despite its toxicity. It has naturalized both here and in other parts of the world where it has been introduced. It prefers moist environments like the banks of streams but is also found in fields, ditches and along roadsides. It has spread so successfully that 12 states consider it an invasive species.

Like its cousin Queen Anne’s Lace, it is a biennial plant with only foliage the first year and then flowers during the second year. I first noticed it last year when it was just foliage. Its flowers this year caught my attention and sent me on my journey of discovery. My research indicates that when crushed, the leaves and root have a rank, unpleasant odor. I have not confirmed that, not wanting to touch a possibly lethal plant.

How Poisonous is Poison Hemlock?

All parts of the plant are poisonous and should be handled with care. Always wear gloves and wash thoroughly afterwards. If you have small children or pets and you find this weed in your yard, it's a good idea to pull it up, place it in a garbage bag and throw it out with your trash. Do not put it in your composter.

Poison hemlock is the hemlock in the fatal drink used to execute Socrates for impiety and corrupting young boys. A lethal dose for a human is 6 to 8 fresh leaves or a few seeds or piece of the root. The poison operates on the central nervous system. Similar to curare, it causes muscular paralysis which spreads throughout the body. When it reaches the respiratory muscles, the victim literally suffocates because he can’t breathe. The only way to survive this is to be put on a ventilator for 48 to 72 hours as the poison gradually wears off.

The poison is also toxic for animals although if ingested in small enough quantities, the animals will survive. If a female is pregnant and survives, her unborn fetus will suffer birth defects. The deer that live in the woodlands in my backyard left this plant alone. They do not eat poisonous plants. Fawns learn from their mothers which plants are safe to eat and which plants are not.

How Do I Tell the Difference Between Queen Anne’s Lace and Poison Hemlock?

There are important differences in the appearance of Queen Anne’s Lace and Poison Hemlock. Poison hemlock is much larger, at 5 to 8 feet. Queen Anne’s Lace is only 1 to 2 feet in height. The flowers are also different. Both have flowers that are referred to as umbels, meaning they are made up of many tiny flowers that held up in an umbrella shape. Queen Anne’s Lace flowers are denser and have the characteristic purple center flower. Poison hemlock flowers are looser and lack a purple flower in the center.

Poison Hemlock flower.  Note that it is more open than Queen Anne's Lace and has no purple flower in the center.
Poison Hemlock flower. Note that it is more open than Queen Anne's Lace and has no purple flower in the center. | Source

There are also distinct differences in the stems and leaves. Queen Anne’s Lace stems and leaves are green and covered with hairs whereas poison hemlock stems and leaves are hairless and the stems have distinctive purple blotches on them making them easy to identify even when the plants are not blooming.

Poison Hemlock stem.  Always look for the purple splotches.
Poison Hemlock stem. Always look for the purple splotches. | Source

Wildflowers are an attractive part of the landscape but appearances can be deceiving. Exercise an abundance of caution when gathering bouquets and keep a close eye on children and pets. Don’t allow them to handle or taste any plant unless you are positive that it is safe.

Questions & Answers

  • Can poison hemlock have a yellow flower?

    No, the flowers are always white which is why it is often confused with Queen Anne's Lace.

  • Where can I find poison hemlock?

    It prefers moist environments like the banks of streams but is also found in fields, ditches and along roadsides. It has spread so successfully that twelve states consider it an invasive species, so you shouldn't have any problem locating it somewhere near you.

© 2017 Caren White


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    • OldRoses profile imageAUTHOR

      Caren White 

      3 years ago

      I agree, Sharon! But people who are not familiar with plants might make that mistake. Thanks for reading and commenting.

    • blueheron profile image

      Sharon Vile 

      3 years ago from Odessa, MO

      I myself don't think poison hemlock looks anything like Queen Anne's lace.


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