A number of trees commonly found across the U.S. contain toxic compounds that can harm people, pets, or livestock if ingested or even touched. According to data from the U.S. Department of Agriculture (USDA), Centers for Disease Control and Prevention (CDC), and university agricultural extensions, these species have been linked to poisoning incidents ranging from mild illness to fatalities. Below are twelve harmful trees that homeowners should avoid planting in their yards.
Oleander: The Deadly Ornamental
Oleander (Nerium oleander) is a widely planted ornamental shrub in warmer U.S. regions, but it is one of the most toxic plants in the world. All parts contain cardiac glycosides that can cause nausea, irregular heartbeat, and death in severe cases. Even inhaling smoke from burning oleander branches is poisonous. The ASPCA warns it is especially dangerous for dogs, cats, and horses.In Italy (2011-2021), 62 oleander poisoning cases were reported none fatal though 43% involved individuals with psychiatric history
Yew: Attractive but Extremely Toxic
Yew trees (Taxus species) are popular in landscaping for their evergreen foliage, but their needles, seeds, and bark contain taxine alkaloids. Ingesting even a small amount can cause sudden cardiac failure in humans and animals. According to Cornell University’s Department of Animal Science, livestock deaths from eating yew clippings are well-documented. Of 48 documented human poisoning cases, 42% were fatal often involving intentional ingestion though accidental cases were infrequent . In livestock, as little as 0.5 lb of needles (≈227 g) can fatally poison a horse
Horse Chestnut: Looks Like Food, Acts Like Poison
The horse chestnut (Aesculus hippocastanum) produces seeds resembling edible chestnuts, but they contain aesculin, a toxin that causes vomiting, diarrhea, paralysis, and sometimes death if consumed in quantity. Reports in the Journal of Veterinary Toxicology highlight cases of poisoning in dogs and livestock that mistook the nuts for safe food.
Black Locust: Toxic Beauty with Fragile Wood
The black locust (Robinia pseudoacacia) grows quickly and produces fragrant flowers, but its bark, leaves, and seeds contain robin and phasin toxins. These substances can cause weakness, depression, and colic in horses and cattle. The USDA notes that even fence posts made from black locust can leach toxins if chewed by livestock.
Angel’s Trumpet: Stunning but Dangerous
Angel’s trumpet (Brugmansia species) is admired for its large trumpet-shaped flowers, yet all parts contain tropane alkaloids such as scopolamine and atropine. Exposure can cause hallucinations, paralysis, or respiratory failure. According to the National Capital Poison Center, recreational misuse of this plant has led to numerous hospitalizations and fatalities.
Cherry Laurel: Hidden Cyanide Risk
Cherry laurel (Prunus laurocerasus) is a common hedge plant, but its leaves and seeds contain cyanogenic glycosides that release cyanide when crushed. The North Carolina State University Extension reports that ingestion can cause difficulty breathing, seizures, and death in pets and humans. Birds also face poisoning risks when consuming the seeds.
White Cedar: Toxic Evergreen for Livestock
White cedar (Melia azedarach), also known as chinaberry tree, is naturalized in many U.S. states. Its leaves, bark, and berries contain neurotoxins such as meliatoxins. The Merck Veterinary Manual notes that ingestion leads to gastrointestinal upset, ataxia, and sometimes fatal seizures in cattle, sheep, and poultry.
Castor Bean Plant: Source of Lethal Ricin
The castor bean plant (Ricinus communis) is sometimes grown ornamentally for its striking foliage, but its seeds contain ricin, one of the deadliest plant toxins known. Ingestion of just one seed can be fatal to a child. The CDC classifies ricin as a potential bioterrorism agent due to its extreme potency.
Poison Sumac: Severe Skin Irritant
Poison sumac (Toxicodendron vernix) thrives in wetlands across the eastern U.S. and is far more toxic than poison ivy or poison oak. Contact with its leaves or stems releases urushiol oil, which causes severe allergic dermatitis. The American Academy of Dermatology notes that even inhaling smoke from burning sumac can lead to dangerous respiratory reactions.
Rosary Pea: Tiny Seeds with Fatal Power
Rosary pea (Abrus precatorius) produces attractive red and black seeds often used in jewelry, but they contain abrin, a toxin even more potent than ricin. According to the National Institutes of Health, ingestion of a single seed if chewed can be lethal. Cases of accidental poisoning have been reported when jewelry beads cracked. In a study of 112 patients with ingestion, the mortality rate was 5.35% with all fatalities involving crushed seeds. Even one chewed seed can be lethal. Case reports include an 18-month-old child surviving after ingestion, and another who developed central pontine myelinolysis a rare neurological injury
Strychnine Tree: The Source of Deadly Poison
The strychnine tree (Strychnos nux-vomica) is rarely cultivated but occasionally found in U.S. collections. Its seeds contain strychnine, a neurotoxin historically used as rat poison. Exposure causes severe muscle spasms, convulsions, and death. The World Health Organization identifies strychnine as a highly hazardous pesticide not suitable for home environments.
Daphne: Beautiful Shrub with a Dangerous Secret
Daphne shrubs (Daphne species) are valued for their fragrant flowers, yet their berries and sap contain daphnetoxin and mezerein. The University of California’s toxic plant database warns that ingestion causes intense burning sensations, nausea, and organ failure. Even skin contact with the sap can produce painful blisters.
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