Every spring our plants awake from their winter’s rest ready to grow new leaves, buds and flowers. Among the beautiful tulips and tomato starts is a weed to keep an eye on: poison hemlock (Conium maculatum). As the name announces, this noxious weed is poisonous to people, pets, livestock, and wildlife. But please don’t let this stop you from controlling the poison hemlock on your property! The problem with poison hemlock comes from ingesting (eating) or inhaling (mowing or burning) it. Poison hemlock can be safely controlled with the right gear (gloves, sleeves, pants), a bit of effort, a trash bag, and a shovel. This post will discuss how to identify poison hemlock, its impacts, what to do if you find it, and how to remove it.
Check out our Poison Hemlock Factsheet for a printable PDF that includes more on the identification, impacts, and control options for this weed.
How to identify poison hemlock
The first step to controlling or reporting weeds, is making sure that you have the right one! Poison hemlock is in the carrot/parsley family and has a lot of less concerning look-alikes.
Click through the photos below to see poison hemlock’s identifying features.
Impacts of poison hemlock
Poison hemlock is best known for its toxic traits, but it also has an impact on our environment.
Public Health
The biggest potential impact of poison hemlock is on public health. Fatal poisoning from this plant is most often caused by accidental ingestion. Eating or breathing in the plant can lead to respiratory failure; its toxins cause the respiratory system to freeze up, leading to asphyxiation. In humans, signs of poisoning can look like nausea, vomiting, pupil dilation, muscle tremors, etc. There is not an antidote for these toxins, so medical care looks like treatment of the individual’s symptoms.
TLDR: The main risk for this plant is eating it, followed by inhaling it (mowing, burning, etc.). Extensive skin contact with the plant can cause issues, but is not as much of a concern.
If someone eats poison hemlock or has symptoms after exposure they need to get medical help immediately. Call poison-control for advice and resources at 1-800-222-1222.
Poisoning is avoidable – click on EACH concern below to learn more.
Concern #1: INGESTING IT
Every part of the poison hemlock plant is toxic and ingesting it can be deadly. It is part of the carrot family and unfortunately resembles many of its edible kin (carrot, parsnip, cilantro, parsley, etc.). Note: poison hemlock is not the only toxic member of the carrot family, but is indeed the most toxic. Misidentification of poison hemlock as an edible plant (and then eating it) is the main reason people have been hospitalized or worse in relation to this species. Never eat a wild plant unless you are 100% certain you have identified it correctly. (2nd opinions are valuable in any type of foraging). This risk (ingestion) can be avoided by not eating any parts of a foraged/garden plant unless you are 100% confident in its identification.
What about pets?
All parts of the plant are toxic to pets and livestock too. Symptoms in pets are similar to humans, but vary slightly, more on this here. Thankfully the plant puts off a distasteful smell that many animals avoid, but not all. That said, for dogs that put anything they see in their mouths, be safe and know this plant so you can avoid it on walks and control it in green spaces. Livestock are more likely to consume this plant than dogs or cats, but will usually not graze on poison hemlock unless they lack other good forage. They’re more likely to eat the bottled/taller plants than the low growing ones. This risk (animal consumption) can be avoided by providing adequate forage for livestock and keeping it out of grazing areas, especially once they bolt and flower. If you think your animal has consumed this plant, seek veterinary support immediately – symptoms often show within an hour. If you can, bring a sample of the plant to show your medical team.
Concern #2: INHALING IT
The 2nd most common reason people have been hospitalized for this plant is due to accidentally inhaling the toxins when unknowingly mowing or burning. This happens when the plant particles are small and near enough to be breathed in in large quantities. The risk of inhaling the toxins increases with hotter weather, longer exposure, and poor air circulation. This is why you should never mow, weed-whack, or burn this plant. In rarer cases, even digging the plants in the wrong conditions (long hours of continual exposure to broken up plants with poor air circulation and hot/still air) has proven to be a risk. This risk (inhalation) can be avoided by not mowing or burning the plant in any conditions, and taking breaks while digging and possibly postponing digging if the conditions are not right.
Concern #3: TOUCHING IT
While it is best to avoid skin contact with the plant, accidents happen and touching the plant alone should not be a cause for panic. The toxins of this plant are in the sap and the issue with touching mostly arises with extensive skin contact, especially through an open wound; or by ingesting toxins by handling the plant/sap and not cleaning your hands before eating, biting nails, wiping eyes, etc. If left on the skin, the sap can irritate the skin and cause dermatitis – always wash up after working with this plant. This risk (skin contact) is avoidable by wearing protective gear (gloves, sleeves, pants) and always washing exposed skin after working with the plant.
Environmental health
Poison hemlock also impacts our local natural areas by growing faster (and often earlier) than native species. Without intervention, this spread can prevent our healthy biodiverse plant communities from flourishing.
A major way people can help is by keeping this plant from flourishing on property they own or manage. Even if you know not to eat or mow it, someone else may not, and seeding plants on your property could end up on theirs.
What to do if you find it
Your options vary based on where you find the plant(s)! Select an option below to learn more about what to do if you find poison hemlock in these places.
ON YOUR PROPERTY
Control it if you are able! More on this in the next section.
If you are not physically able to control the poison hemlock you have, there are many workers for hire who are happy to help. King County residents can email us at noxious.weeds@kingcounty.gov for a list of contractors who can help. If hiring help is beyond your means, email us your situation and we can try our best to get you support.
ON SOMEONE ELSE’S (PRIVATE) PROPERTY
If it feels safe – talk to them! Many people are simply unaware of this plant. There is no legal requirement for private landowners to control their poison hemlock, so unfortunately, we cannot help much in these situations beyond providing resources. If you aren’t comfortable talking to them, we have a weed alert/fact sheet that you can print and leave as appropriate.
ON PUBLIC PROPERTY (in King County, WA)
In King County, poison hemlock is legally required to be controlled on any public property, rights-of-way, and railroads. The manager/owner of said property is the responsible agency; please note that these groups have varying degrees of resources and capacity and potentially already know about the infestation.
Follow the steps below if you wish to report an infestation on public property in King County. Please note – many public groups have limited resources around weed control and may not get to your report immediately. They will get to it as soon as they can!
- Take clear photos! Many plants look like other plants, and even if you’re confident, groups will want a clear photo to verify the species before moving forward with your concern.
- Note the exact location (cross streets, park name, nearby address, etc.)
- Know who owns/manages the property (responsible agency.)
- Not sure who owns the property? You can use the King County Parcel Viewer to find out by typing the address in the top left search bar or finding it on the map.
- Once you find the property, click on it and note the taxpayer name (this is the responsible agency.)
- Find their contact information, it’s often public and easily found with a web search! Search “[agency name] contact information” or “report a problem [agency name]”.
- Contact them as appropriate (email, reporting portal/site, phone call, etc.)
- Make sure your communication includes: poison hemlock, public requirement, photos, and location details.
- Have patience as groups often have a long queue of reports to work through. Even if the infestation isn’t controlled this season, it has likely been noted and will be on next year’s plan.
Please note that the legal requirements noted above only apply to King County, Washington.
How to control and dispose of poison hemlock
Here’s the good news, you can help get rid of this weed! After a few years of persistent removal, you won’t see poison hemlock popping up in the early spring.
For a more detailed look at poison hemlock ID, impact, & other control options (including chemical), check out our fact sheet here: Poison Hemlock (Conium maculatum) – King County Noxious Weed Factsheet
Check out our 1-minute video on manual poison hemlock control below.
Manual control 101 (video recap)
- Never mow or burn! Be sure to take fresh air and water breaks, especially if circulation is poor (hot, humid, minimal wind).
- Always wear gloves, sleeves, & pants to avoid skin irritation.
- Smaller patches & individual plants can be dug up at any growth stage. Get the whole root! Digging is easiest in soft soils (spring & fall) but possible in compact soils (tip: water soil the day before for easier removal!).
- If flowering/seeding – be sure to cut, bag, & dispose of those parts as a priority.
- Seedlings can be scraped away with a hoe or similar tool.
- Optional: add a 4-6 inch layer of mulch to any bare soil in removed area to help prevent seedlings.
- Bag all parts & discard in garbage (not compost bin).
- Wash any exposed skin & hands thoroughly after handling plants, wash clothes as usual.
- After your initial control – plan for maintenance! Pull seedlings when you see them. You should see less and less every year.
County-wide control efforts
The Noxious Weed Control Program has been coordinating county-wide control of poison hemlock on public lands and railroad rights-of-way since 2019. Staff survey past and new sites each year. This data is shared with land managers who control the weeds. When our team has capacity, we occasionally do control work as well. In 2023 we controlled 14 acres of poison hemlock across 538 sites.
Looking ahead
Poison hemlock presents a challenge to preserving green space and public health. Each plant can produce 40,000 seeds and each seed may remain viable for up to six years. When you see a poison hemlock plant in your neighborhood, you’ll probably keep seeing poison hemlock plants in future years.
This can be discouraging, however with a few years of consistent control we can see great success. Control of poison hemlock is relatively simple compared to some weeds that require chemical intervention. 2024 is only our fifth season of regulating poison hemlock and already we’ve seen 14 sites that have no re-growing plants! Pulling together we can make a difference for our natural areas, farms and community gardens.