If you enjoy spending time in your yard or the Wisconsin woods, you should know about the poisonous plants in Wisconsin. Some are deadly and surprisingly common, growing right under our noses in gardens, fields, and forests. Recognizing them is the first step to keeping yourself, your children, and your pets safe.
This guide will help you identify these plants. We’ll cover what they look like, where they grow, and what to do if someone is exposed. Knowledge is your best defense.
Poisonous Plants In Wisconsin – Deadly And Surprisingly Common
Wisconsin’s landscape is beautiful, but it hides some dangerous residents. From pretty wildflowers to invasive weeds, several plants pack a toxic punch. Let’s look at the most hazardous ones you’re likely to encounter.
Water Hemlock (Cicuta maculata)
Often called the most violently toxic plant in North America. All parts are poisonous, especially the roots.
- Identification: Grows 3 to 6 feet tall. Has smooth, hollow stems with purple streaks. Leaves are toothed and lance-shaped. Small white flowers form in umbrella-like clusters.
- Where it grows: Loves wet areas. Look for it in marshes, along stream banks, and in ditches.
- The Danger: Contains cicutoxin, which attacks the central nervous system. Ingestion can quickly lead to violent seizures, stomach pain, and can be fatal. There is no antidote.
Deadly Nightshade (Atropa belladonna) & Related Nightshades
This group includes both rare and common plants, all with toxic alkaloids.
- Identification: Deadly Nightshade itself is uncommon but has dull green leaves, bell-shaped purple flowers, and shiny black berries. More common is the Climbing Nightshade (Bittersweet Nightshade), a vine with purple star-shaped flowers and red berries.
- Where it grows: Gardens, forest edges, and disturbed soils.
- The Danger: Berries are the biggest risk, especially to kids. Symptoms include dilated pupils, confusion, hallucinations, and trouble breathing.
Poison Hemlock (Conium maculatum)
Not to be confused with water hemlock, but just as dangerous. It’s the plant that killed Socrates.
- Identification: Can reach 8 feet tall. The stem is hairless with distinctive purple blotches. Leaves are fern-like. Flowers are small and white, arranged in umbrella clusters.
- Where it grows: Thrives in full sun. Found along roadsides, in vacant lots, and at the edges of fields.
- The Danger: Contains coniine alkaloids. Ingesting any part can cause muscle paralysis and respiratory failure. The roots are mistake for wild parsnips, which is a terrible error.
Foxglove (Digitalis purpurea)
A popular garden ornamental that is deceptively dangerous.
- Identification: Tall spikes (2-5 feet) of tubular, bell-shaped flowers. Colors range from purple and pink to white. Leaves are large, fuzzy, and form a rosette at the base.
- Where it grows: Commonly planted in flower gardens. It can also escape and grow wild.
- The Danger: Contains digitalis, used in heart medicine but poisonous in raw form. Eating leaves, flowers, or seeds can cause nausea, vomiting, severe heart rhythm problems, and death.
Wild Parsnip (Pastinaca sativa)
A widespread invasive that causes severe skin reactions, not internal poisoning.
- Identification: Looks like a tall, yellow-flowered Queen Anne’s Lace. Grooved, hairless stem. Yellowish-green flowers in a flat-topped cluster.
- Where it grows: Roadsides, pastures, and abandoned fields.
- The Danger: Sap contains chemicals called furanocoumarins. When sap gets on skin and is exposed to sunlight, it causes painful, blistering burns (phytophotodermatitis). Scars can last for months.
Moonseed (Menispermum canadense)
A tricky look-alike for wild grapes, making it a common cause of poisoning.
- Identification: A woody vine that climbs. Leaves are heart-shaped, similar to grape leaves. The key difference is the fruit: moonseed has a single, crescent-moon-shaped seed, while grapes have multiple round seeds.
- Where it grows: Woodlands, thickets, and along streams.
- The Danger: All parts are poisonous, but the dark purple berries are most often eaten by mistake. They can cause seizures and be fatal.
Jimsonweed (Datura stramonium)
A foul-smelling plant with a long history of causing poisoning.
- Identification: Large, trumpet-shaped white or purple flowers. Has spiky seed pods. Leaves are coarsely toothed.
- Where it grows: Disturbed soils, barnyards, and along roads.
- The Danger: Every part is toxic. It causes intense hallucinations, delirium, rapid heart rate, and can be deadly. People sometimes mistakenly use it for its psychoactive effects with tragic results.
How to Identify Poisonous Plants: A Step-by-Step Guide
Don’t rely on just one feature. Use a careful, multi-step process to make a safe identification.
Step 1: Look at the Whole Plant
Note its size, shape, and how it grows (upright, vine, shrub).
Step 2: Examine the Leaves
- Shape (heart, lance, fern-like)?
- Edge (smooth, toothed, lobed)?
- Arrangement on stem (alternate, opposite)?
- Texture (hairy, smooth, waxy)?
Step 3: Inspect the Stem
- Color and markings (purple blotches on poison hemlock)?
- Texture (hairy, smooth, thorny)?
- Is it hollow or solid? (A key clue for water hemlock).
Step 4: Check the Flowers and Berries
Color, shape, and how they are clustered (umbels, spikes, single). Berries are a major risk factor.
Step 5: Consider the Habitat
Is it in a wet ditch, dry field, sunny garden, or shady woods? Location rules out many possibilities.
Step 6: Use a Trusted Field Guide or App
Compare your findings to photos from reliable sources like the UW Extension or a reputable plant ID app. When in doubt, assume it’s dangerous.
What to Do If Exposure Happens
Act quickly and calmly. Here’s what you need to do.
For Skin Contact (Like Wild Parsnip):
- Immediately wash the area thoroughly with soap and cool water.
- Remove contaminated clothing carefully.
- Keep the area out of sunlight for at least 48 hours to prevent worsening the reaction.
- See a doctor for blistering or severe rash. They can prescribe treatments to reduce scarring.
For Ingestion (If Someone Eats a Plant):
- Call the Poison Control Center immediately: 1-800-222-1222. Do not wait for symptoms.
- Do not induce vomiting unless instructed by a professional.
- If possible, identify the plant. Take a picture or bring a sample with you.
- Note how much was eaten and when.
- Go to the emergency room if advised by Poison Control or if the person has trouble breathing, seizures, or loses consciousness.
Protecting Children and Pets
Curious kids and animals are at the highest risk. Proactive measures are essential.
In Your Own Yard:
- Learn to identify every plant in your garden and landscaping.
- Remove any known poisonous plants. Wear gloves, long sleeves, and eye protection when removing them.
- Teach children never to put any part of a plant in their mouth. Supervise them closely outdoors.
On Walks and Hikes:
- Keep dogs on a leash in areas where poisonous plants may grow.
- Train your dog to “leave it” when they sniff at plants.
- Know the symptoms of pet poisoning: vomiting, diarrhea, drooling, lethargy, or unusual behavior. Contact your vet immediately.
Common Look-Alikes: Don’t Be Fooled
Many edible or harmless plants have dangerous twins. Here are the most confusing pairs.
Wild Carrot (Queen Anne’s Lace) vs. Poison Hemlock
Both have white umbel flowers. Queen Anne’s Lace has a hairy stem, often with a single purple flower in the center, and smells like carrot. Poison Hemlock has a hairless, purple-blotched stem and smells musty or like mouse urine.
Wild Grapes vs. Moonseed
Check the seeds! Wild Grapes have 2-4 round, pear-shaped seeds. Moonseed has a single, flat, crescent-shaped seed. Grapes also have forked tendrils; moonseed’s tendrils are not forked.
Elderberry vs. Water Hemlock
Elderberry is a woody shrub with opposite leaves and flat clusters of berries. Water Hemlock is a herbaceous plant with alternate leaves and always grows in wet soil. Never, ever mistake the root.
Managing and Removing Poisonous Plants Safely
If you find these plants on your property, removal must be done with caution.
For Non-Skin-Irritants (Like Hemlock):
- Wear gloves, long pants, a long-sleeved shirt, and closed-toe shoes.
- Dig out the entire root system. These plants often resprout if cut.
- Place all plant parts in a heavy-duty garbage bag. Do not compost or burn them, as fumes can be toxic.
- Wash your tools and clothing seperately after.
For Skin-Irritants (Like Wild Parsnip):
- Wear waterproof gloves, goggles, and full clothing coverage.
- Cut the plant at the base before it seeds, using tools to avoid contact.
- Bag and dispose of it in the trash.
- Wash any potentially exposed skin immediately.
When to Call a Professional:
For large infestations of dangerous plants like poison hemlock, consider hiring a landscaper or invasive species removal service. Your safety is worth the cost.
FAQ: Poisonous Plants in Wisconsin
What is the most deadly plant in Wisconsin?
Water hemlock is considered the most deadly due to the potency of its toxin and the speed of its effects. Even a small amount of the root can be fatal.
Are poisionous plants common in Wisconsin gardens?
Some, like Foxglove and Lily of the Valley (which is also toxic), are very common ornamentals. Others, like poison hemlock, invade from roadsides. It’s important to know what you’re planting.
Can you get a rash from touching poisonous plants in Wisconsin?
Yes. Wild parsnip causes severe chemical burns. Others, like stinging nettle (which is not seriously poisonous but painful), cause temporary rashes. Always wear gloves when handling unknown plants.
What should I do if my dog eats a wild berry?
Try to identify the plant immediately. Contact your veterinarian or the Pet Poison Helpline. Symptoms like vomiting or unusual behavior mean you need to get help right away.
How can I learn more about plant identification?
The University of Wisconsin-Madison Extension has excellent resources. Consider joining a local plant walk with a naturalist or using field guides specific to the Great Lakes region.
Are mushrooms included in lists of poisonous plants?
Mushrooms are fungi, not plants, but they are a serious poisoning risk. Many deadly mushrooms grow in Wisconsin. Never eat a wild mushroom unless identified by an expert.
Staying safe around Wisconsin’s flora means respecting it. By learning to recognize these hazardous plants, you can enjoy the natural beauty of the state with confidence. Take the time to look around your own neighborhood—you might be suprised at what you find, and now you’ll know what to do.