Poisonous plants in Wisconsin can be toxic and cause serious health issues if ingested. Depending on the particular species, these poisonous plants can cause anything from minor skin irritation to organ failure, and in some cases, even death.

Guide to Poisonous Plants in Wisconsin

This post contains a list of the poisonous plant species that can be found in the badger state. Check out their descriptions below.

Different Kinds of Poisonous Plants in Wisconsin

1. Poison Ivy

Understanding and Avoiding Poison Ivy

Growing Season
  • Spring
  • Summer
Leaf Shape Rounded
Specific Needs
  • Moist but well-drained soil
  • Partial shade or full sunlight
Common Pests
  • Beetles
  • Flies

Poison ivy is a native Wisconsin plant that contains urushiol oil, an allergen that can cause severe skin and mucous membrane inflammation on contact. It has distinctive leaves with three leaflets, which have this sap in them and would harm a person just by a single touch. Poison ivy is found in shady hedgerows, woodland edges, thickets, and wetlands throughout the state.

When you find it, specific care should be taken to avoid contact; when people come into direct contact with this plant’s leaves, stems, or roots they may become sensitized to urushiol oil, leading to itchy rashes, swelling, and blisters. Which means that in order to avoid this hazard, one should be mindful to avoid every single contact. 

2. Stinging Nettle

Identifying and Handling Stinging Nettle

Growing Season
  • Fall
  • Spring
Leaf Shape Heart-shaped
Specific Needs
  • Part shade or full sunlight
  • Moist nutrient-rich soil
Common Pests
  • Hover-flies
  • Lacewings
  • Parasitic wasps

Stinging nettle is a poisonous invasive species in Wisconsin. Its upper stem has small glandular hairs that can cause a stinging sensation when poked or brushed against. Ingesting the plant or getting it in contact with mucous membranes can cause immense discomfort, including skin irritation and burning sensations. These would promote a stressful situation, hence you must be careful and inform others, and in care it happens, some measures should be taken.

This plant has a strong adverse impact on Wisconsin’s native ecosystems, as it is grown rampantly and obscures out light, nutrients, and water from other native plants.

3. Cow Parsnip

The Dangers of Cow Parsnip

Growing Season
  • Summer
  • Spring
Leaf Shape Lobed
Specific Needs
  • Partial Shade
  • Wet Soil
Common Pests
  • Flies
  • Aphids

Cow parsnip is a large and fast-growing member of the carrot family (Apiaceae) that is native to Wisconsin and eastern North America. It features white flower clusters atop large stems reaching up to seven feet tall.

Although some people enjoy wild edible leaves and seeds, this plant can cause serious health problems when ingested, especially in humans with skin sensitivity, and it would depend on from one person to the other. This reaction is caused by chemical compounds in its sap known as furanocoumarins and psoralens which are highly phototoxic to both human and animal systems.

4. Poison Hemlock

Consequences of Mistaking Poison

Growing season All year round
Leaf shape Triangular
Specific needs
  • Moist soil
  • Part or full sunlight
Common pests Aphids

Poison hemlock or Conium Maculatum is a poisonous plant native to Wisconsin and is found throughout most of the United States. It is a member of the carrot family and has similar characteristics to garden vegetables, such as wild carrots or parsley, however, this one has an irritating characteristic while others don’t.

This perennial herb can grow up to eight feet tall. Once ingested, this plant can be fatal due to its toxic sap called the alkaloid coniine, it will affect the central nervous system and can cause respiratory failure. Which means that you should definitely run and see a medical professional to help you as soon as possible. 

5. Wild Parsnip

Recognizing and Avoiding Wild Parsnip

Growing season Summer
Leaf shape Diamond-like shape
Specific needs
  • Moist to mesic soil
  • Partial or full sunlight
Common pests Parsnip webworm

Wild parsnip is a highly invasive, poisonous plant species that is native to Europe and Asia but has become established in Wisconsin. It belongs to the same family as carrots and is recognized by its yellow flower heads appearing atop stems reaching between two and six feet in height.

Aside from being an unsightly nuisance, wild parsnip can cause severe rash or blistering if one is exposed to its sap directly on their skin due to a chemical compound called phoranburon. Under any ultra violet light, the skin will become pretty vulnerable and intolerant to the damage that it has caused. 

6. Wood Nettle

Understanding the Risks of Wood Nettle

Growing season Summer
Leaf shape
  • Oval
  • Ovate
Specific needs
  • Full sunlight or part shade
  • Acidic soil
Common pests Red admiral caterpillar

Wood nettle is a common poisonous plant found in Wisconsin and across the United States. It can be identified by its irregularly-shaped, jagged leaves and small white or greenish flowers, which grow up to one inch long.

The wood nettle’s stem is distinctly square-shaped with hairs on all four angles. This plant contains toxic compounds known as cardenolides that cause an intense burning sensation even when one comes to a very soft touch towards it, it will. The effects of touching this plant can last for days, which means that the body is very vulnerable towards its acid-like burn. 

7. Jimson Weed

Hallucinogenic of Jimson Weed

Growing season Spring
Leaf shape Oval
Specific needs
  • Full to partial sunlight
  • Fertile rich soil with
Common pests Beetles

Jimson eeed is a highly toxic plant that is native to Wisconsin. It contains tropane alkaloids, which can cause serious harm if ingested or absorbed through the skin. This weed has an extremely unpleasant odor making it difficult for humans and animals to consume it.

Jimson weed can be found in disturbed areas of grassy fields or roadsides. Ingestion of the leaves, flowers, or seeds can lead to symptoms such as dryness of the mouth and difficulty swallowing. However, some have even experienced a very strong amount of intoxication that it has even resulted in death, in different cases. 


8. ArrowheadToxicity of Arrowhead Plant

Growing season Summer
Leaf shape Spade-like
Specific needs
  • Bright indirect sunlight
  • Moist soil
Common Pests
  • Mealybugs
  • Spider mites
  • Sphids

Arrowhead is one of the most common poisonous plants found throughout Wisconsin. It is easily identified by its white or yellowish-white, lance-shaped foliage and small yellow flowers.

Consumption can lead to severe stomach distress, nausea, vomiting, however, when one gets to inject it in a very large dose, it would even result in death because the immune system doesn’t have the strength to overcome that big of a quantity.

All parts of this plant are potentially harmful and it should be handled with extreme caution when foraging for edibles on outdoor expeditions in the area.

9. Grecian Foxglove

Consequences of Grecian Foxglove

Growing Season Summer
Leaf Shape Oblong
Specific Needs
  • Full morning sun
  • Afternoon light shade
  • Loamy acidic soil
Common Pests
  • Praying mantises
  • Ladybugs

Grecian foxglove is a highly toxic plant native to eastern and southeastern Europe, but in recent years it has become an invasive species in parts of North America, especially Wisconsin. This perennial herb can grow up to three feet tall and produces clusters of tubular flowers with white, pinkish, or purplish petals speckled on the interior.

Its leaves are extremely poisonous when ingested due to its high content of digitalin, a cardiac glycoside with powerful heart-stimulating properties that can lead to arrhythmia or even death. However, when it is in a smaller dose, make sure that you would rush to a medical expert and the faster you get the treatment, the faster it will heal you from the intoxication.

10. Daphne

Poisonous Properties of Daphne

Growing Season
  • Winter
  • Spring
Leaf Shape
  • Oblong
  • Elliptic
Specific Needs
  • Fertile slightly acidic soil
  • Filtered sunlight
Common Pests Aphids

Daphne is a poisonous, evergreen shrub native to the Mediterranean region, but can also be found in regions of North America, particularly Wisconsin. It produces small yellowish-green flowers.

The plant contains high levels of toxins known as diterpenoid furanocoumarins which can cause skin blistering and irritation when touched. Also note that when this plant is ingested orally in large doses it poses health risks such as vomiting, abdominal cramping, and even death if left unchecked by medical professionals. 


There are different kinds of poisonous plants in Wisconsin as you have seen in this post and they are found in different seasons of the months, for example,

  • Various plants like wild parsnip, wood Nettle, arrowhead, etc. thrive during summer.
  • Plants such as poison Ivy or cow parsnip grow in both spring and summer.
  • During the winter season, Daphne can be found growing around Wisconsin.
  • Stinging Nettle is a plant that can be seen thriving during fall.

If you can keep an eye out for these plants based on their growing season, you can easily avoid coming into contact with them.

5/5 - (5 votes)
Evergreen Seeds