Home & Garden Garden 18 Poisonous Plants and Flowers Some wild plants pose a hidden danger. Stay away to avoid illness or even death. By Bryan Nelson Bryan Nelson Twitter Writer SUNY Oswego University of Houston Bryan Nelson is a science writer and award-winning documentary filmmaker with over a decade of experience covering technology, astronomy, medicine, animals, and more. Learn about our editorial process Updated August 4, 2022 Share Twitter Pinterest Email Treehugger / Catherine Song Home & Garden Planting Guides Indoor Gardening Urban Farms Insects Over the past millennia, people have learned through trial and error which plants are good to eat and which are best to avoid. In our modern, urban world, much of that cultural knowledge has been forgotten. Many gardeners may be surprised to discover that they are growing some of the world's deadliest plants in their own backyards. Here are several plants with lethal tendencies. 1 of 18 Apples Artotem / Flickr / CC BY 2.0 An apple a day might keep the doctor away, but the same can't be said for apple seeds. The seeds contain cyanogenic glycosides, making them mildly poisonous. If you consume enough of the seeds, by chewing, mashing, or breaking them apart in some way, you could ingest a fatal dose. But that's a lot of apples. Although the number of seeds varies from apple to apple, as does the exact amount of cyanide-releasing glycosides, the adult of average weight would need to finely chew and eat about 222 apple seeds, or about 26 apple cores, to receive a fatal dose. Much less would be harmful to children. According to one study, seeds of Golden Delicious apple varieties contain more cyanide-releasing glycosides than other types. But no matter the variety, whether you cut up apples for your children or eat them whole, be sure to remove the seeds to be on the safe side. 2 of 18 Deadly Nightshade Melanie Shaw / Flickr / CC BY-ND 2.0 The name says it all—both the foliage and the berries of this plant are extremely toxic. Deadly nightshade has a long, colorful history of use as a poison, but what many people don't realize is that the nightshade family includes common food plants, including potatoes, tomatoes, eggplants and chili peppers. In fact, all of these plants contain toxins—usually in their foliage—that can be harmful. In particular, humans and pets should avoid potato and tomato foliage and vines in the garden. 3 of 18 Rosary Pea CanerCakir / Getty Images This plant may sound pious, but it's actually deadly. Rosary peas got their name from their traditional use as ornamental beads for rosaries. They are used in jewelry around the world, and are also called jequirity beans. The poison contained within the seed is abrin—a close relative of ricin and one of the most fatal toxins on Earth. 4 of 18 Oleander Swaminathan / Flickr / CC BY 2.0 Oleander is one of the most toxic, commonly grown garden plants in the world. Ingesting any part of this plant can be deadly, especially for children. Even smoke from burning oleander can be fatal. The plant's use as a poison is well-known. One study estimates the fatality rate among oleander poisoning cases to be between 6 and 10 percent. 5 of 18 European Yew DM / Flickr / CC BY-ND 2.0 Relatively common in Europe, northwest Africa and the Middle East, nearly all parts of this slow-growing tree can be poisonous. The exception is the red fleshy aril that surrounds the toxic seeds. The aril is frequently eaten by birds. Ingesting the leaves or the seeds, both of which contain a poison called taxane, can cause death. Symptoms of poisoning can include a fast heart rate, muscle spasms and labored breathing. 6 of 18 Daffodils Russell James Smith / Flickr / CC BY 2.0 Prized for their beauty, daffodils grow from bulbs that could be mistaken for an edible food, like an onion. Daffodils—also known by their genus name Narcissus—are common ornamental plants with a bright, cheery flower. Most daffodils are deer- and vermin-resistant, but gardeners shouldn't overlook the dark side of this plant. All parts of the daffodil contain a toxin called lycorine. The most poisonous part of the plant is the bulb, as it has the highest concentration of lycorine, but eating any part of a daffodil can cause nausea, vomiting, and other symptoms. The Greek philosopher Socrates sometimes referred to daffodils as the "Chaplet of the infernal Gods" because of the plant's numbing effect. 7 of 18 Doll's Eye benet2006 / Flickr / CC BY 2.0 It's a good thing the creepy-looking berries of this plant aren't enticing, because consuming the fruit of a doll's eye plant (or white baneberry) could kill you. The berries contain cardiogenic toxins that can have an immediate sedative effect on cardiac muscle tissue. Symptoms of poisoning include burning of mouth and throat, salivation, severe stomach cramps, headache, diarrhea, dizziness and hallucinations. Ingestion of the berries can eventually lead to cardiac arrest and death. 8 of 18 Hemlock Feifei Cui-Paoluzzo / Getty Images This is one of the most famous poisonous plants in history—it's the flora responsible for killing Socrates. All parts of the plant contain the relatively simple alkaloid coniine which causes high blood pressure, vomiting and progressive paralysis of the central nervous system. Hemlock is also known by several common names, including devil's porridge, beaver poison or poison parsley. 9 of 18 Stinging Tree N. Teerink / Wikimedia Commons / CC BY-SA 4.0 Found in forests in Queensland in Australia and Indonesia, Dendrocnide moroides is one of the most painful and potent stinging nettles in the world. Accidentally brushing past any part of this plant or its stinging relatives can deliver a potent toxin that will cause a painful stinging sensation lasting for days or even months. A severe sting from this plant will cause a severe allergic reaction and even death in horses and dogs; one human death has been reported. (One researcher documented her time working with Dendrocnide excelsa, which is considered a less dangerous plant, and her increasingly allergic reaction to the plant offers a sense of what's possible.) 10 of 18 Castor Beans Noppharat05081977 / Getty Images If you have consumed castor oil before, you might be surprised to learn that castor beans contain one of the most poisonous substances in the world, ricin. Just one castor bean has enough ricin to kill a child within a few minutes. Despite this grim quality, castor bean plants are frequently grown for decorative purposes, even in parks and public places. 11 of 18 Angel's Trumpet Michael Davis / Getty Images Angel's trumpets are woody-stemmed bushes with pendulous flowers that hang like bells. They are prized as decorative additions to the garden because of their elegant flowers. The catch is that all parts of these plants contain dangerous levels of poison and may be fatal if ingested by humans or animals. Angel's trumpets have occasionally been used to create a recreation drug, but the risk of overdose is so high that these uses often have deadly consequences. 12 of 18 Monkshood typo-graphics / Getty Images Monkshood has a long tradition as a deadly plant and was used by ancient warriors to carry out executions. It was also once used as a popular werewolf repellent. In 2014, a gardener died of multiple organ failure after brushing past this deadly purple flowering plant on the estate where he was working in the U.K. 13 of 18 White Snakeroot Andrei Stanescu / Getty Images White snakeroot contains the toxin tremetol, which can be poisonous if consumed directly or second-hand. When snakeroot is eaten by cattle, the animals' beef and milk become contaminated with the toxin, and ingesting those substances can lead to a condition called milk sickness. Abraham Lincoln's mother, Nancy Hanks, reportedly died after swallowing snakeroot-contaminated milk. Human disease is uncommon today because of current practices of animal husbandry and the pooling of milk from many producers, but milk sickness does still occur. 14 of 18 Larkspur Natasha Wakefield / Getty Images The seeds and young plants of the larkspur are toxic to both people and animals. Toxicity decreases as the plant ages. Larkspur has several alkaloids including delphinine, delphineidine, ajacine and others that can cause very unpleasant issues. According to the U.S. Department of Agriculture (USDA) symptoms of poisoning include general weakness and muscle spasms, as well as abdominal pain and nausea. Eventually, it can lead to respiratory distress, paralysis and death. Larkspur is responsible for heavy livestock losses, according to the USDA, particularly with cattle in Western states when the animals are allowed to graze where the plant is abundant. 15 of 18 Foxglove liz west / Flickr / CC BY 2.0 The seeds, stems, flowers and leaves of the foxglove plant are poisonous. They contain digitalis glycosides, which are organic compounds that act on the heart. When someone eats part of this attractive plants or sucks on the flowers, the glycosides affect cardiac function, causing an irregular heartbeat. Symptoms can also include digestive issues, headache, blurred vision and confusion and could lead to death. 16 of 18 Melia azedarach John Bill / Shutterstock In Australia, it's known as white cedar. But this deciduous tree in the mahogany family is also known as a chinaberry tree, the Pride of India, an umbrella tree and the Persian lilac. Its fruits contain a mixture of poisons, including neurotoxins, which can harm humans (as few as 6 berries can kill a person). Birds, however, can tolerate them, so they eat the fruit and spread the seeds. The flowers on the tree, which is native to Australia and Southeast Asia, are small with light purple and white petals of five, and they often grow in clusters. The fruits are small, spherical and yellow. 17 of 18 Lantana sakchai vongsasiripat / Getty Images These flowers are colorful and bright, but take it as a warning. They're poisonous to humans and animals, and so should not be planted anywhere that you might come into contact with them. Symptoms of poisoning may vary, but gastrointestinal pain and nausea are common, as is shortness of breath. If you do want these flowers, put them in hanging baskets where they can be displayed without risk of contact. 18 of 18 Lily of the Valley Jacky Parker Photography / Getty Images This exquisite and aromatic little bells harbor a dark secret—toxic compounds called cardiac glycosides that can cause vomiting and diarrhea. The roots are most toxic, but all parts of the plant are, with children most commonly being poisoned by the attractive red berries. Keep it far from the reach of anyone who might feel an inclination to ingest it. View Article Sources Diaz, James H. “Poisoning by Herbs and Plants: Rapid Toxidromic Classification and Diagnosis.” Wilderness Environ Med. 2016, vol. 27, pp. 136-52., doi:10.1016/j.wem.2015.11.006 Bolarinwa, Islamiyat F., et al. "A Review of Cyanogenic Glycosides in Edible Plants." In: Toxicology - New Aspects to This Scientific Conundrum. IntechOpen. 2016. doi:10.5772/64886 Bolarinwa, Islamiyat F et al. “Determination of Amygdalin in Apple Seeds, Fresh Apples and Processed Apple Juices.” Food Chemistry, vol. 170, 2015, pp. 437-42., doi:10.1016/j.foodchem.2014.08.083 “The Powerful Solanaceae: Belladonna.” U.S. Forest Service. “Atropa belladonna.” Missouri Botanical Garden. “Facts About Abrin.” Centers for Disease Control and Prevention. Davies M. K., et al. “Oleander Poisoning.” Arch Dis Child., vol. 84, 2001, p. 9., doi:10.1136/adc.84.1.9 Umakanth, M. “Prevalence of Yellow Oleander (Thevetia peruviana) Poisoning in Eastern Part of the Sri Lanka.” Saudi Journal of Medical and Pharmaceutical Sciences, 2017, doi:10.21276/sjmps.2017.3.10.14 “Yew Toxicology in Domestic and Wild Species.” Cornell University. Piskac, Ondrej, et al. “Cardiotoxicity of Yew.” Cor et Vasa, vol. 57, iss. 3, 2015, pp. E234-e238., doi:10.1016/j.crvasa.2014.11.003 “Daffodils at Shaw Nature Reserve.” Missouri Botanical Garden. “Daffodils. Beautiful but Potentially Toxic.” National Capital Poison Control. Cordell, Geoffrey. The Alkaloids, Volume 63. Elsevier Science. 2006. “Actaea pachypoda.” North Carolina State University Extension. Hotti, Hannu, and Heiko Rischer. “The Killer of Socrates: Coniine and Related Alkaloids in the Plant Kingdom.” Molecules (Basel, Switzerland), vol. 22, iss. 11, 1962, 2017., doi:10.3390/molecules22111962 Erenier, Ali Kemal, et al. “A Case of Respiratory Failure Due to Poison Hemlock Poisoning Presented to an Emergency Department.” Hong Kong J. Emerg. Med., vol. 18, iss. 4, 2011, pp. 235-238. doi:10.1177/102490791101800408 Gilding, Edward K., et al. "Neurotoxic Peptides from the Venom of the Giant Australian Stinging Tree." Sci Adv., vol. 6, no. 38, 2020, doi:10.1126/sciadv.abb8828 Maor, Danit, et al. “Skin Contact with a Stinging Tree Requiring Intensive Care Unit Admission.” Contact Derm, vol. 77, iss. 5, 2017, pp. 335-337., doi:10.1111/cod.12830 Schmitt, Connie, et al. "Painful Sting After Exposure to Dendrocnide sp: Two Case Reports." Wilderness Environ Med., vol. 24, iss. 4, 2013, pp. 471-3., doi:10.1016/j.wem.2013.03.021 “Facts about Ricin.” Centers for Disease Control and Prevention. “Ricin Toxin from Castor Bean Plant, Ricinus communis.” Cornell University. Kim, Yonn, et al. “Intoxication by Angel's Trumpet: Case Report and Literature Review.” BMC Res Notes, vol. 7, p. 553., doi:10.1186/1756-0500-7-553 “Aconitum napellus (Monkshood): A Purple Poison.” National Capital Poison Center. Dolan, Laurie C., et al. “Naturally Occurring Food Toxins.” Toxins (Basel), vol. 2, iss. 9, 2010, pp. 2289-2332., doi:10.3390/toxins2092289 Westbrooks, Randy G., and James W. Preacher. “Poisonous Plants of Eastern North America.” University of South Carolina Press. 1986. “Department of Animal Science - Plants Poisonous to Livestock.” Cornell University. Berdanier, Carolyn D., et al. Handbook of Nutrition and Food, Second Edition. CRC Press. 2007. “Larkspur (Delphinium spp.).” U.S. Department of Agriculture. “Foxglove Poisoning.” Mount Sinai. “Foxglove Poisoning.” MedlinePlus. “Melia azedarach.” Australian National Herbarium. “Melia azedarach.” North Carolina State University Extension. Gupta, Sanjay Mohan, et al. “Himalayan Toxic Plants of Defense Importance.” ACTA Scientific Medical Sciences, vol. 2, iss. 3, 2018.