Invasive plant
Poison hemlock
Conium maculatum
Poison hemlock identification: a smooth, hollow stem with purple blotches and fern-like leaves. All parts are toxic if eaten; wear gloves when handling.
Published Last reviewed
Do not handle poison hemlock until you are sure what it is. All parts are toxic if eaten, and the sap can irritate skin. If a person has eaten any part of the plant, call Poison Control at 1-800-222-1222 now; if they have collapsed, are seizing, have trouble breathing or cannot be woken, call 911.
Touching it and eating it are not the same risk
The serious danger is eating the plant. Penn State Extension says all parts of poison hemlock are toxic to humans and other animals, and that the roots and seeds contain the highest concentration of alkaloids. King County says eating even a small amount of any part can kill people, livestock and wildlife.
Skin contact is a different risk. Penn State Extension describes the sap as toxic and a skin irritant, and says even weed trimming needs precautions so plant material does not touch the body. King County puts it in proportion: skin contact alone typically will not cause a reaction severe enough to need medical treatment, but the sap can cause a serious reaction in some people. If you get sap on your skin, wash it off with soap and warm water as soon as possible. Wash your hands after handling plants, and wash your clothes. If you are not sure whether an exposure needs medical care, call Poison Control at 1-800-222-1222.
Do not taste the plant to identify it. Do not put it in your mouth, and do not let children or pets chew on cut stems.
The stem test
Poison hemlock is in the carrot family, so it blooms with white umbrella-shaped clusters that look like several other plants. The stem is the fastest way to narrow it down.
- Poison hemlock: smooth and hairless, hollow, ridged, with reddish-purple spots and streaks. Sources report it at 3 to 10 feet tall in flower, with regional differences; Penn State gives up to 6 feet.
- Queen Anne’s lace: 1 to 3 feet tall, with a stem covered in bristly hairs. The white flower cluster is 2 to 4 inches wide and usually has a tiny deep-purple flower in the center.
- Wild parsnip: up to 5 feet tall, with yellow flowers and a grooved, hairless stem.
- Giant hogweed: much larger, usually 7 to 14 feet tall, with coarse white hairs and deeply cut leaves. Its sap can cause severe burns.
- Water hemlock: a native plant that is also highly toxic. Its leaf veins end in the notches between the teeth; poison hemlock veins end at the tooth tips.
Our poison hemlock vs Queen Anne’s lace comparison puts the stems side by side and gives the flower-head checks. For the other deadly look-alike, see water hemlock vs poison hemlock.
Why the first-year rosette is the target
Poison hemlock is a biennial. The first year it stays low as a rosette of fern-like leaves. The second year it sends up the tall flowering stem, sets seed and dies. Penn State Extension says the most effective approach is to treat the first-year rosettes, not the larger mature plant. That makes late summer and fall a good time to find next year’s problem while it is still small.
Do not wait for the flowers to open. King County says seed typically starts to form by early August, and a single plant can produce more than 30,000 seeds. Those seeds can remain viable in the soil for up to six years, so one pull is not the end of the job.
Remove it without making it worse
- Put on gloves, long sleeves, long pants and eye protection before you touch it.
- Pull or dig the plant, and try to remove the entire taproot. Work when the soil is moist.
- Bag the plant material and put it in the regular trash. Do not compost it or put it in yard waste.
- Avoid a weed trimmer or brush cutter. If you must mow, wear a mask over your mouth and nose, and stop if you feel sick.
- Wash your hands, tools and clothes afterward.
If the stand is large, is next to water, or is in a pasture with livestock, stop and call your extension office or state agriculture department before you start. Those sites have different herbicide restrictions and a bigger margin for error.
What to do this week
- Confirm the smooth, hollow, purple-blotched stem and rule out Queen Anne’s lace.
- If there is any chance a child or animal ate the plant, call Poison Control at 1-800-222-1222.
- Treat or pull the rosettes before the flower stalks rise.
- Bag the debris and keep it out of compost.
For the full method and protective-equipment list, read how to get rid of poison hemlock and the best time to treat invasive plants. More profiles are listed under invasive plants, and image credits are on the image credits page.
Identification
Look for the combination of characters below. A single feature is rarely enough, especially when a native look-alike is present.
- Height and life cycle
- A biennial. The first year is a low rosette of leaves; the second year sends up a flowering stem that is usually 3 to 10 feet tall. Penn State Extension gives up to 6 feet in its region.
- Stems
- Hollow, hairless and ridged, with reddish-purple spots and streaks, especially on the lower stem. New York's comparison table gives a stem diameter of 1 to 2 inches.
- Leaves
- Bright green and fern-like, divided into small toothed segments and resembling parsley or carrot tops. Wisconsin DNR gives a length of 8 to 16 inches and a broadly triangular outline.
- Flowers
- Tiny white flowers with five petals, grouped in flat-topped umbels 4 to 6 inches across. Blooms mostly from May through August, depending on the region.
- Roots and seeds
- A thick white taproot about 10 inches long, plus many fibrous roots. A single plant can produce more than 30,000 seeds.
Look-alikes
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Queen Anne's lace
Daucus carota
Queen Anne's lace is 1 to 3 feet tall and its stem is covered with bristly hairs, not smooth and purple-blotched. Its flat white flower cluster is 2 to 4 inches wide and usually has a small deep-purple flower in the center.
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Wild parsnip
Pastinaca sativa
Wild parsnip grows up to 5 feet tall and has yellow flowers. Its stem is grooved and hairless, but it does not have the purple blotches of poison hemlock.
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Giant hogweed
Heracleum mantegazzianum
Giant hogweed is much larger, usually 7 to 14 feet tall, with coarse white hairs on the stem and much more deeply cut leaves. Its sap can cause severe sun-sensitive burns.
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Water hemlock
Cicuta maculata
Water hemlock is a native plant and is also highly toxic. Its leaf veins end in the notches between the teeth, while poison hemlock veins end at the tips of the teeth.
Range and status
Native range: Europe and Asia
Regulatory status by state
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pennsylvania Noxious weed
Poison hemlock is a Class B noxious weed on the Pennsylvania Department of Agriculture list. Noxious weeds cannot be sold, transported, planted or otherwise propagated in the state. Class B means the plant is widely established and cannot feasibly be eradicated.
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new-york Not on the state noxious-weed list
Poison hemlock is not on the 6 NYCRR Part 575 prohibited or regulated plant list.
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virginia Not on the state noxious-weed list
Poison hemlock is not on any tier of Virginia's noxious weed list in 2VAC5-317-20.
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ohio Noxious weed
Poison hemlock is a prohibited noxious weed under OAC 901:5-37-01. Ohio law requires management of these weeds on public and private property.
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wisconsin Restricted
Wisconsin classifies poison hemlock as Prohibited/Restricted. It is Restricted in 22 named counties and Prohibited elsewhere, which means control rules differ by county. Confirm the rule for your county with the Wisconsin DNR.
Why it matters
All parts of poison hemlock are toxic to people and animals, and eating even a small amount can be dangerous. It also spreads by seed into pastures, roadsides, stream banks and disturbed ground, where it forms tall dense patches. The danger is not only to the person pulling it; it is also to livestock, pets and children who encounter it.
Management
Protect yourself before you start
Wear gloves, long sleeves, long pants and eye protection. Avoid a weed trimmer or brush cutter if you can, because cut material and sap can reach your skin or face. If you must mow, cover your mouth and nose with a mask and stop if you feel sick. Wash any skin that contacts the plant with soap and warm water as soon as possible.
Pull or dig first-year rosettes
Timing: Early spring or fall, before the plant flowers.
Penn State Extension says the most effective approach is to treat first-year rosettes, not large mature plants. King County advises pulling or digging at any growth stage before seed set and removing the entire root. Work when the soil is moist, and bag the plant material.
Treat before the flowers open
Penn State Extension names diquat, pelargonic acid, glyphosate and 2,4-D as postemergent active ingredients. Wisconsin DNR lists 2,4-D plus dicamba applied before buds form. Follow the product label; the label is the law. Near water, use only an aquatic-labeled product.
Bag it, do not compost it
Put pulled plants in a plastic trash bag and discard them with regular trash. Do not put poison hemlock in yard waste or compost, and do not leave an accessible pile where children, pets or livestock can reach it.
Stop seed for more than one year
Seeds typically start to form by early August, and King County reports that seed can live up to six years in the soil. Control before seed set, then monitor the site for several seasons.
Sources
Facts on this page were checked against the sources below. Each link shows the date the source was accessed.
- Poison Hemlock — Penn State Extension Accessed November 3, 2026
- Poison hemlock (Conium maculatum) — Wisconsin Department of Natural Resources Accessed November 3, 2026
- Poison hemlock identification and control — King County, Washington Accessed November 3, 2026
- Giant Hogweed and Common Lookalikes — New York State Department of Environmental Conservation Accessed November 3, 2026
- Poison Control — National Capital Poison Center Accessed November 3, 2026
- Conium maculatum L. (poison hemlock) — USDA NRCS PLANTS Database Accessed November 3, 2026
- Controlled Plant & Noxious Weed Lists — Pennsylvania Department of Agriculture Accessed November 3, 2026
Related pages
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Poison Hemlock vs Queen Anne's Lace: The Stem Test
Poison hemlock vs Queen Anne's lace: a smooth, purple-blotched stem means hemlock; a bristly, hairy stem means Queen Anne's lace. If unsure, do not touch.
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Water Hemlock vs Poison Hemlock: The Leaf-Vein Test
Water hemlock vs poison hemlock identification: both are deadly. Poison hemlock leaf veins end at tooth tips; water hemlock veins end in the notches.
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How to Dispose of Invasive Plants Safely
How to dispose of invasive plants: bag roots, tubers and seed heads, solarize the sealed bags, then trash them. Do not compost or send them to yard waste.
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How to Get Rid of Invasive Plants Without Chemicals
How to get rid of invasive plants without chemicals: pull, dig, cut on a schedule, smother or solarize. Where vinegar and boiling water fall short.
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How to Get Rid of Invasive Plants: A Step-by-Step Guide
How to get rid of invasive plants: identify it, check state rules, choose a method by root type, dispose of every fragment, then monitor regrowth.
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How to Get Rid of Poison Hemlock Safely
How to get rid of poison hemlock safely: cover your skin, target first-year rosettes before they bolt, and bag every piece. Never burn it.
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Spring Invasive Plants Checklist: What to Look For in March, April, May and June
Spring invasive plants checklist: what to look for and act on each month from March through June, with links to species and removal guides.