Poison Hemlock Guide: What it Looks Like & How to Get Rid of It from Your Garden

Conium maculatum is better known by its common names hemlock, wild hemlock, and of course poison hemlock. Because despite the fact that their leaves resemble the tasty parsley you might sprinkle over your pasta or add to your salads, all parts of this pretty plant are indeed rather poisonous, poison hemlock is also sometimes called fool’s parsley.

Poison hemlock belongs to the Apiaceae botanical family of flowering plants, making it a distant relative of fennel, carrots, parsley, and dill, as well as the also severely poisonous giant hogweed. The genus Conium has six officially recognized species.

Poison hemlock is native to Europe, specifically the Mediterranean region, but is now prolific in much of the UK as well and has become naturalized to the United States, too.

There’s no denying that Conium maculatum is a beautiful plant. The charming and delicate white flowers, which grow in abundant clusters that resemble the shape of an umbrella, are their most aesthetically-pleasing feature.

However, due to the severe poison profile, poison hemlock isn’t a plant you should want around in your garden, sadly. This weedy plant is quite hard to eradicate, but with the right steps, you can get it under control.

About Poison Hemlock

• Poison hemlock is a herbaceous biennial with complex deep green compound leaves that taper into a single tip. Its beautiful flower clusters are poison hemlock’s most striking feature. The flowers are usually white, but can also be pink.
• This poisonous plant is native to Europe, and was originally brought to the Americas in the nineteenth century, when it was originally sold as a winter fern. Poison hemlock has not been too much of a concern historically, but has recently began spreading prolifically in nearly all states, prompting the National Park Service and numerous news outlets to publish warnings about the plant.
• Conium maculatum resembles Queen Anne’s Lace (Daucus carota) which belongs to the same family quite closely. If you are not certain which of the two plants you are looking at, we would strongly recommend that you look at pictures of all parts of both plants to differentiate them. Do not rely on written descriptions of the plant’s features.
• Poison hemlock is in no way related to “hemlock” (Tsuga canadensis) and similar species — these coniferous trees are an entirely different species.
• The genus Conium was appropriately named — the Greek word from which it originates, koneios, means spinning or whirling — because eating any part of the plant can give you vertigo. Because the fact that ingesting any part of this plant is extremely dangerous, not just to humans but to all mammals and even many animals that aren’t mammals, we’ll deal with the potential consequences of hemlock poisoning, and what to do if you suspect a person or pet has eaten it, in a separate section.
• Because poison hemlock thrives in poorly-draining, soggy, soil, the plant can usually be found growing on waterlogged wastelands, along roads, and in ditches. In the US, this has become a particular problem in the midwest, which has been subjected to wet spring periods that poison hemlock loves to capitalize on. Conium maculatum flowers during the summer, after which the plant releases tens of thousands of seeds. These are, many people have already been warned, easy to scatter when mowing the lawn, causing the highly invasive plant to begin thriving in your garden.
• All plants are beautiful in their own way, and we don’t want to only say negative things about this beautiful plant that so many people are so desperate to get rid of. On the upside, poison hemlock attracts and supports some rare butterfly and moth species. Poison hemlock moths and silver-ground carpet moths depend on this plant, as their larvae feed on it.
• The fact that even small amounts of poison hemlock can be deadly greatly inspired Shakespeare and John Keats, and hemlock is even mentioned in the Bible.

Poison Hemlock Features: An Overview

A word of warning — although written descriptions of a plant’s features can be helpful, there are some other plants, notably parsley and Queen Anne’s Lace, that look quite a bit like poison hemlock. To identify poison hemlock with the greatest degree of certainty, you would be advised to look at pictures, examining all physical characteristics closely.

• Conium maculatum is a herbaceous perennial with an upright growth habit and vibrant green leaves, charming white flower clusters, and a fleshy taproot.
• These large flowering plants can grow to be five to eight feet (one and a half to two and a half meters) tall, and do not have a very wide spread.
• The shiny compound leaves of the poison hemlock plant have a vibrant green color. Arranged in clusters with a triangular shape, the pinnately divided leaf clusters of the poison hemlock are remarkably large — they can be as long as 20 inches (50 centimeters) and 16 inches (40 centimeters) wide. Succinctly said, the leaf clusters look like ferns.
• The color of Conium maculatum‘s singular stem, from which multiple branches protrude at roughly a 45 degree angle, can vary quite widely. The stem may have a copper-brown, green, burgundy, or even deep purple shade. The distinctive feature, which can also be used to tell poison hemlock apart from similar-looking plants, is that poison hemlock has completely smooth and hairless stems.
• Poison hemlock produces deceptively showy flowers, which have five petals each. These flowers grow at the end of long stalks in large clusters, forming umbels. Each cluster of flowers will also have some brown bracts below it. Poison hemlock flowers during the summer.
• After the flowers recede, poison hemlock produces tiny seeds, which are easily carried by the wind, causing the plant to proliferate.
• You can typically find Conium maculatum in areas with lots of water — around ponds, in woodlands, and near streams, for instance. They quickly take over any uncultivated area, however, and are also often seen along roads or in ditches. If you’re not careful, poison hemlock may soon find its way to your garden, too.

What Are the Symptoms of Hemlock Poisoning?

Every single part of Conium maculatum is poisonous — that means the bark, stem, leaves, flowers, seeds, fruits (which cover the seeds when first released), roots, and the sap.

Poison hemlock is not only poisonous to people, but also to every other mammalian species. Your pets and farm animals, whether cats, horses, dogs, sheep, cows, or goats can all die as a result of ingesting poison hemlock — and so can you or your children.

The toxicity of poison hemlock does vary through its growth cycle, and the symptoms and severity of hemlock poisoning depend on this as well as the quantity that was ingested. The first symptoms can set in anywhere from half an hour to several hours after eating any part of the plant, and they include:

• Trembling or shaking
• Increased salivation
• Nausea and vomiting
• Diarrhea, sometimes with visible bleeding
• Extreme discomfort of the digestive tract, most often described as a burning feeling
• Muscle weakness and even paralysis
• Dilated pupils
• Initially, a racing heart — and later, a worrying slowing of the heart rate and a weak pulse
• Losing the ability to speak
• Trouble breathing due to paralysis of the respiratory tract
• Convulsions
• Coma
• Death
• In livestock, skeletal birth defects have been reported after an animal ingests poison hemlock during pregnancy

As if all that didn’t sound scary enough already, there’s another important thing to be aware of before you think that this poisonous plant, too, deserves a little love, and you’d actually love to keep this beautiful “underdog” around in your garden. There’s no antidote to hemlock poisoning.

That means that people and animals who are dealing with hemlock poisoning can only be offered supportive care. Each of the symptoms will be treated individually — and patients will be offered fluids to support their recovery. Medical professionals, whether doctors or veterinarians (depending on the victim) can try to speed up the removal of the poison, but cannot offer a definitive cure.

You know what that means — where there is no cure, prevention becomes the cure. If you have Conium maculatum in your garden, you are living with a ticking time bomb. You need to eliminate it. If you are, by any chance, a fan of the modern foraging movement that has recently become popular, you need to be very well-versed in plant identification. Poison hemlock certainly isn’t the only plant or fungus you could mistake for a tasty snack.

Do note that poison hemlock is actually not among the plants that will cause contact dermatitis, so touching it shouldn’t immediately cause you to panic. All the problems associated with poison hemlock occur after eating it, but even small amounts can be extremely hazardous. Despite that fact, you are warmly recommended to don gloves, face masks, and other protective gear before interacting with poison hemlock.

What Not to Do With Poison Hemlock

If you have spotted poison hemlock in or near your garden, you may be tempted to simply mow the plant down.

Not only does this come with the obvious disadvantage that you would be leaving the plant’s strong and sturdy root system in place (meaning that poison hemlock will definitely come back to haunt you), but you’d also risk:

• Spraying the extremely poisonous sap (which can also release toxic fumes) all over your garden, and perhaps into your face.
• Spreading the seeds of Conium maculatum far and wide, causing the flowering plants to appear in numerous new locations. In other words, multiplying the problem.

Cutting the stems down poses a similar problem, and is therefore not recommended either.

Burning the plant down is another non-recommended strategy to its elimination, because the fumes resulting can irritate the airways severely, especially in sensitive groups.

How to Get Rid of Poison Hemlock

Four viable approaches to eliminating poison hemlock, a highly invasive plant, exist. They are manual, mechanical, chemical, and biological.

1. Manually Removing Poison Hemlock From Your Garden

To manually remove poison hemlock, you are advised to don personal protective equipment and to ensure that vulnerable people and animals are nowhere near the site. Dig around the location of the plant to safely remove it by its roots, taking care not to leave any part of the roots in place. Once removed from the soil, place the poison hemlock in a plastic garbage bag, even using several layers of bags. Do not compost these plants as they will return with a vengeance.

2. Mechanical Ways to Control Poison Hemlock

Your average gardener should not necessarily attempt this, but some people choose to mow Conium maculatum with a weed eater before their growing season starts, and before they start flowering or producing seeds. This will leave the root systems in place. That is why this kind of removal must immediately be followed up by mulching, the planting of other prolific (but non-poisonous) plants who can quickly take over the area, or both. This may be done in wastelands, and not in gardens where people often spend time.

3. Using Herbicides to Kill Poison Hemlock

Herbicides are an effective approach when used in the early spring. Typically, Weedmaster and Milestone are recommended. These herbicides should applied to the entire plant’s surface, while the gardener is wearing personal protective equipment (including long sleeves). It may have to be repeated several times.

4. Biological Control: Poison Hemlock Moths

The larvae of these moths only feed on poison hemlock, and can be a relatively effective way to control the plant’s growth.

Do all of those options sound equally intimidating to you, and are you 100 percent sure you have poison hemlock in your garden? Calling a landscaping company that is confident about their ability to manage highly poisonous plants is a great solution to your problem.