If you enjoy spending time outdoors in Illinois, knowing about poisonous plants is important for your safety. This guide covers the common poisonous plants in Illinois that are dangerous to humans and pets you might encounter in your yard, on hikes, or in natural areas.
We’ll help you identify them, understand the risks, and learn what to do if contact or ingestion happens. Being informed is the first step to preventing unpleasant and potentially serious situations for your family and furry friends.
Poisonous Plants In Illinois – Dangerous To Humans And Pets
Illinois is home to a diverse range of native and ornamental plants, and a number of them carry natural defenses in the form of toxins. These toxins can cause reactions from mild skin irritation to severe internal illness or even death. The risk is present in both wild settings and cultivated gardens, making identification a key skill for any resident.
Why Plant Poisoning Happens
Accidental poisoning often occurs out of curiosity, especially with children and pets. Bright berries and attractive leaves can be tempting. Sometimes, people misidentify wild plants as edible, like mistaking poison hemlock for wild carrot. Even brushing against some plants while gardening or walking can trigger a reaction.
General Safety Rules
Follow these basic rules to stay safe:
- Teach children never to put any part of a plant in their mouth unless an adult says it’s safe.
- Supervise pets in the yard and on walks, especially in new areas.
- Learn the names of all plants in your garden and landscape.
- Wear gloves, long sleeves, and pants when handling unknown plants or weeding.
- Wash your hands thoroughly after gardening.
Plants Primarily Dangerous Through Skin Contact
These plants can cause painful rashes and irritation just by touching them. The effects are usually external but can be very uncomfortable.
Poison Ivy
This is perhaps the most infamous plant in Illinois. It grows as a vine, a ground cover, or a small shrub. Remember the phrase: “Leaves of three, let it be.” Each leaf cluster has three glossy leaflets, with the middle one on a longer stalk. The edges can be smooth or notched. All parts of the plant—leaves, stems, roots—contain urushiol oil year-round.
- Reaction: Contact causes an itchy, red rash with bumps or blisters, often appearing in lines. It is not contagious from the blisters themselves, but the oil can spread on skin, clothing, or pet fur.
- What to Do: Wash the skin with cool water and soap as soon as possible. Wash all clothing and gear. Use calamine lotion or hydrocortisone cream for itching. See a doctor for severe reactions or if the rash is on the face or genitals.
Poison Oak
Less common than poison ivy in Illinois, it still appears in some areas. It also has leaves in groups of three, but they resemble oak leaves with rounded lobes and a fuzzy texture. It usually grows as a low shrub.
- Reaction: Identical to poison ivy—an itchy, blistering rash from urushiol oil.
- What to Do: Same immediate treatment as poison ivy.
Wild Parsnip
This invasive plant grows in sunny areas like roadsides and fields. It has tall, grooved stems and clusters of small yellow flowers. The danger comes from the sap, which contains chemicals called furanocoumarins.
- Reaction: When sap gets on skin and is then exposed to sunlight, it causes a severe burn-like reaction called phytophotodermatitis. This leads to painful blisters, reddening, and can cause long-term skin discoloration.
- What to Do: Immediately cover the affected skin from sunlight. Wash thoroughly with soap and water. Treat like a burn. Keep the area out of the sun for at least 48 hours. A doctor should see severe blistering.
Plants Primarily Dangerous If Ingested
These plants pose the greatest risk if any part is eaten. The effects range from stomach upset to critical organ failure.
Poison Hemlock
This plant is extremely toxic and can be fatal. It grows very tall (up to 8 feet) with hollow, purple-spotted stems and lacy clusters of small white flowers. It smells unpleasant, like mouse urine. It is often found in ditches, along fences, and in moist waste areas. It looks similar to Queen Anne’s Lace or wild carrot, but those do not have purple-spotted stems.
- Reaction (Humans & Pets): Ingestion affects the nervous system. Symptoms include trembling, salivation, dilated pupils, muscle weakness, rapid heartbeat, and can progress to respiratory failure and death. Even a small amount is dangerous.
- What to Do: This is a medical emergency. Call 911 or poison control immediately. Do not induce vomiting unless directed by a professional.
Deadly Nightshade (Belladonna) & Related Nightshades
While less common, various nightshade species grow in Illinois. They often have purple or white star-shaped flowers and produce berries. The berries are the biggest risk, especially to children.
- Reaction: Ingestion causes symptoms like dilated pupils, sensitivity to light, blurred vision, headache, confusion, hallucinations, convulsions, and tachycardia. The severity depends on the amount eaten.
- What to Do: Seek immediate medical attention. Try to bring a sample of the plant for identification.
Castor Bean
This is sometimes grown as an ornamental plant for its large, tropical-looking leaves. It produces spiky seed pods containing highly toxic beans. The toxin is ricin, which is extremely potent.
- Reaction: Chewing or ingesting even one bean can be fatal. Symptoms include severe abdominal pain, vomiting, diarrhea (which may become bloody), seizures, and kidney failure.
- What to Do: This is a life-threatening emergency. Go to a hospital or call 911 immediately.
Oleander
This shrub is sometimes planted in gardens or kept as a container plant in Illinois, though it is not winter-hardy statewide. It has long, narrow dark green leaves and produces beautiful white, pink, or red flowers. Every part of this plant is poisonous.
- Reaction: Ingestion affects the heart, causing irregular heartbeat, low blood pressure, and can be fatal. It can also cause severe digestive upset.
- What to Do: Contact poison control or seek emergency care right away. Even smoke from burning oleander wood is toxic.
Plants Dangerous to Pets (Especially Dogs & Cats)
Many plants that cause mild issues in humans can be much more severe for pets due to their smaller size and different metabolism. Here are some common ones in Illinois landscapes.
Lilies (True Lilies: Easter, Tiger, Asiatic, Daylilies)
This is critical for cat owners. True lilies (Lilium and Hemerocallis species) are highly toxic to cats. Ingesting any part—petal, leaf, pollen, or even water from the vase—can cause acute kidney failure.
- Reaction (Cats): Vomiting, lethargy, loss of appetite within hours. Without rapid veterinary treatment, it leads to kidney shutdown and can be fatal within 3-7 days.
- What to Do: If you suspect your cat has contacted a lily, take them to a veterinarian immediately. Do not wait for symptoms to appear.
Sago Palm
This popular houseplant and outdoor ornamental in warmer months is highly toxic to dogs. All parts are poisonous, but the seeds (nuts) are the most concentrated.
- Reaction (Pets): Vomiting, diarrhea, lethargy, seizures, and liver failure, which is often fatal.
- What to Do: Immediate veterinary care is essential. The prognosis worsens rapidly after symptoms begin.
Autumn Crocus
Not to be confused with the spring crocus, the autumn crocus blooms in fall. It contains colchicine, which is highly toxic.
- Reaction (Pets & Humans): Causes severe vomiting, gastrointestinal bleeding, liver and kidney damage, respiratory failure, and can be fatal.
- What to Do: This is an emergency. Seek veterinary or medical help without delay.
Azalea & Rhododendron
These common flowering shrubs contain grayanotoxins. Ingestion of even a few leaves can cause problems.
- Reaction (Pets): Excessive drooling, vomiting, diarrhea, weakness, leg paralysis, low blood pressure, coma, and potentially death.
- What to Do: Contact your veterinarian. They will likely advise you to bring your pet in for treatment.
Common Garden Plants with Toxic Parts
Many ornamental plants we grow have mild to moderate toxicity. Awareness helps prevent accidents.
- Daffodils & Tulips: The bulbs are the most toxic part, causing nausea, vomiting, and diarrhea if ingested. Can be a problem for dogs that dig.
- Foxglove: Beautiful but contains digitalis, which affects heart rhythm. All parts are toxic.
- Lily of the Valley: Contains cardiac glycosides. Small, bell-shaped flowers and red berries are a risk.
- Hydrangea: Leaves and flower buds contain cyanogenic glycosides, which can cause stomach upset.
- Yew: This evergreen shrub’s needles and seeds are highly toxic, causing sudden heart problems. The red berry flesh is not toxic, but the seed inside is.
What to Do in Case of Exposure or Ingestion
Staying calm and acting quickly is vital. Here are the steps to follow.
For Skin Contact (Like Poison Ivy)
- Remove contaminated clothing carefully.
- Rinse the skin immediately with lukewarm water and soap for at least 10 minutes. Use rubbing alcohol if available before washing with water.
- Scrub under fingernails with a brush.
- Wash all clothing, tools, and pet fur that may have contacted the plant.
- Use cool compresses, calamine lotion, or hydrocortisone cream to manage itching.
- See a doctor if the rash is widespread, on the face, or shows signs of infection.
For Ingestion (Suspected Plant Poisoning)
- Stay Calm. Panicking won’t help.
- Remove any plant material from the person’s or pet’s mouth.
- Identify the plant. Take a photo or bring a sample with you. This is crucial.
- Call for help immediately:
- For Humans: Call the National Poison Control Center at 1-800-222-1222. They provide free, expert guidance 24/7.
- For Pets: Call your veterinarian, an emergency animal clinic, or the ASPCA Animal Poison Control Center at (888) 426-4435 (fee may apply).
- Do not induce vomiting unless explicitly instructed to by the professional on the phone.
- Follow their instructions precisely and go to the nearest emergency room or veterinary clinic if told to do so.
Making Your Yard Safer
You can enjoy a beautiful and safer outdoor space with some planning.
- Identify and Remove: Learn what’s growing in your yard. Safely remove highly toxic plants like poison hemlock or castor bean. For poison ivy, you may need to use specific herbicides or hire a professional.
- Choose Safe Alternatives: When planting, opt for non-toxic species. Some great native Illinois options include Purple Coneflower, Black-eyed Susan, and Coreopsis.
- Create Physical Barriers: Use fencing or plant cages to keep pets away from garden beds with potentially harmful plants.
- Supervise and Train: Always supervise young children and pets outdoors. Train dogs with commands like “leave it.”
- Proper Disposal: Do not compost or burn poisonous plants. Place them in sealed bags for trash disposal to avoid further exposure.
Frequently Asked Questions (FAQ)
What are some common toxic plants found in Illinois backyards?
Common backyard risks include lily of the valley, azalea/rhododendron, yew shrubs, daffodil and tulip bulbs, foxglove, and oleander (in containers). Always check plant labels before purchasing.
How can I tell poison hemlock from Queen Anne’s Lace?
Look for purple spots on the stem—poison hemlock has them, Queen Anne’s Lace does not. Poison hemlock also grows taller and has a hairless, smooth stem with a foul odor when crushed.
Are there any Illinois plants that are poisonous to touch?
Yes. Poison ivy, poison oak, and wild parsnip are the primary ones. Stinging nettle also causes a temporary, painful sting but is not typically considered “poisonous” in the same way.
What should I do if my dog eats a mushroom or unknown berry in the park?
Treat it as a potential poisoning. Try to get a sample of what they ate, note how much, and call your vet or animal poison control immediately. Do not wait for symptoms.
Is it safe to burn poison ivy vines?
No, it is extremely dangerous. Burning poison ivy releases urushiol particles into the air, which can be inhaled and cause a severe internal reaction in the lungs and airways. Always dispose of it in the trash.
Where can I get help identifying a plant I think might be poisonous?
You can contact your local University of Illinois Extension office. They have master gardeners who can help with identification. You can also use reputable plant identification apps or field guides, but be cautious and confirm with an expert if there is any doubt.
Knowledge is your best defense against the risks posed by poisonous plants in Illinois. By learning to recognize the most dangerous species, practicing caution in unknown areas, and knowing the steps to take in an emergency, you can greatly reduce the risk to yourself, your children, and your pets. Take the time to look around your own property and local walking routes—it’s a simple step that fosters a safer environment for everyone to enjoy the natural beauty of the state.