Plants That Kill: Tour the Alnwick Poison Garden

Behind the 900-year-old stone walls of Alnwick Castle, the sinister side of botany blooms. Join us, if you dare, as we discover plants that have the power to poison, blind and kill.

October 16, 2020

By: Julie Martens Forney

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Alnwick Poison Garden

Bone-chilling botany takes center stage in the Poison Garden at Alnwick Castle in Northumberland, U.K. This morbid garden features potent plants that earn a turn in the spotlight for one reason only: being lethal to humans. What’s most surprising about these plants is how common they are. You may even have a few growing innocently in your garden. Take a virtual tour of the Alnwick Poison Garden — if you dare!

Famous Façade

Guarded by stone-carved lions, Alnwick Castle in the Northumberland region dates back to the 11th century. Look familiar? You may know it as Brancaster Castle in Downton Abbey or Hogwarts School of Witchcraft and Wizardry in the Harry Potter movies.

Step Inside

The Alnwick Poison Garden with its foreboding flora is part of 14 acres of gardens that have earned Alnwick Castle Gardens the nickname “Versailles of the North.” Poison Garden guided tours are free after you pay the entry fee to the castle gardens. Tours operate every half hour until 5 p.m.

The Deadliest Garden

Inside the Poison Garden, more than 100 dangerous plants grow under lock and key. Some are so hazardous they’re cultivated inside cages. This is definitely one garden where you don’t want to stop and smell the flowers. The Duchess of Northumberland created this morbid collection to help educate schoolchildren about the dangers of harmful and illicit drugs — the kinds of compounds these plants produce. Visitors to the garden are warned not to touch, smell or even stand near the plants.

Black Henbane

Pale yellow flowers with black-veined petals and a dark center have earned black henbane (Hyoscyamus niger) a common name of devil’s eyes. Leaves of this herb emit a noxious odor that can be overwhelming, especially on a warm day in the walled Poison Garden. Visitors frequently collapse or even faint when they come near this plant, which is why there’s a bench nearby — and first aiders on standby. Because henbane was an important tool in herbal medicine of the ancient world, settlers carried seeds to the New World. Today the plant has spread throughout the Northeast, Midwest and West. All parts of this plant are poisonous to people and livestock.

Giant Hogweed

In terms of perilous plants, giant hogweed (Heracleum mantegazzianum) is a definite contender for a top spot. With flowers that resemble dainty queen anne’s lace and a size that rivals Jack’s beanstalk, giant hogweed is tough to miss. Plants tower 8 to 14 feet high, an impressive size that’s tempting to pose beneath. But don’t be so fast to sidle up to this giant menace. Its sticky sap has the power to burn your skin, causing blisters (of the third-degree burn kind) that continue to appear for up to seven years. Breaking a mirror has nothing on this poisonous plant! If the sap gets in your eyes, blindness can result. Giant hogweed is reported heavily in the Northeast, Midwest and Pacific Northwest and is slowly spreading across the United States.

Angel’s Trumpet

Perfumed blooms disguise the perilous nature of this exotic beauty. Angel’s trumpet, also known as Brugmansia, is a commonly sold container plant that’s often grown as an annual in cold winter regions. In warmest zones, gardeners typically cultivate it in tree form, allowing the long, trumpet-like blossoms to dangle. Angel’s trumpet is a potent hallucinogenic similar to LSD. Victorian ladies would keep a plant in the home and knock a few pollen grains into a teapot, turning the warm brew into a day-tripping sip for genteel lady visitors. All parts of the plant are toxic.

Cherry Laurel

Alnwick Poison Garden includes a hedging plant that’s popular on both sides of the Atlantic: cherry laurel (Prunus laurocerasus). This fragrant evergreen produces cyanide from broken leaves or stems. During the Victorian era, laurel leaves played a key role in butterfly collections. Pop a butterfly into a jar, drop in a cut cherry laurel leaf, twist the lid on tight, and voila! — a (cyanide-poisoned) butterfly perfect for mounting. Avid British gardeners occasionally complain of headaches and dizziniess due to cyanide poisoning when hauling laurel hedge prunings to the yard waste drop. This event typically occurs on a warm day after clippings have sat in the car with the windows up, allowing cyanide to accumulate. A commonly planted U.S. variety is ‘Otto Luyken.’

Delphinium

A cottage garden classic, delphinium brings spires of beautiful blue blossoms to spring garden scenes. Lurking beneath the surface of this bloomer, however, are compounds that kill. The youngest parts of the plants deliver the most potent poison. In the West, wild delphinium (often called larkspur) kills livestock each year — animals die within a few hours of eating the plant. All parts of delphinium are poisonous, causing symptoms of abdominal pain and paralysis that leads to death. Wear gloves when deadheading, and make sure children or pets do not consume seeds.

Castor Bean

Towering and sculptural, castor bean (Ricinus communis) commands attention in the garden with its deep red, star-like leaves. This tropical beauty hails from East Africa, but has naturalized in warmer regions of North America. In the garden, a plant easily tops 5 feet (or more) in a typical summer growing season. Gardeners love castor bean for its architectural appearance, including chunky seed pods. Seeds contain ricin, one of most deadly natural poisons — 6,000 times more poisonous than cyanide. Four seeds are enough to kill an average-size person. This is the poison used in the infamous umbrella gun in 1978 to take out Bulgarian dissident Georgi Markov on the Waterloo Bridge in London.

Rue

Common rue or herb-of-grace delivers its poison via phytotoxicity — like giant hogweed, it burns skin. Long revered for medicinal and culinary uses, rue (Ruta graveolens) became an herb garden favorite for its pretty appearance: dainty texture and blue-green leaves topped with yellow blooms. These days, it’s fallen out of favor due to its skin-burning properties. At Alnwick Poison Garden, a senior gardener spotted a weed growing up out of a clump of rue. Without thinking (or gloving up), the gardener pulled the weed and got rue sap on her hands. Within an hour, blisters formed on her hands that progressed to third-degree burns. This reaction is caused because the sap removes skin’s natural protection against ultraviolet rays. Once the sap is in your system, it lingers up to seven years.

Foxglove

Beloved for its blossom-packed spires, foxglove (Digitalis purpurea) brings cheerful color to the late spring and early summer garden. Blooms open in a literal rainbow of shades, including yellow, pink, chartreuse and purple. All parts of the plant are poisonous. Digitalis, a heart medicine, is produced from this plant. Often people make tea from the leaves, suck on flowers or nibble seeds. Doing these things is basically taking an unregulated dose of heart medicine, which can affect heart rate (slowing it down or making it irregular). This is a dangerous plant with lethal possibilities.

Pasque Flower

Pasque flower (Pulsatilla vulgaris) steals the spotlight in spring with blooms that open in shades including purple, white, wine-red and yellow. Ferny leaves form an eye-catching tuft. Blossoms, leaves and stems are covered in silvery hairs that add a textural element to the pretty plant. It thrives in dry soil and readily spreads to form a colony if you let it set seed. All parts of the pasque flower plant contain poisonous sap that produces skin irritation and violent convulsions.

Atropa Belladonna

Native to the United Kingdom and naturalized throughout the United States, Atropa belladdonna brings the poison power. Also known as deadly nightshade, this botanic assassin opens purple blossoms that fade to form sweet blue-black berries. Four berries can kill a child. During the Italian Renaissance in Venice, ladies of the court would drop juice from the berries into their eyes, which caused pupils to dilate and cheeks to flush — cosmetic tricks to enhance beauty (and eventually lead to blindness and death).

Daffodil

Spring’s sunny flower, the daffodil, is another member of the poison plant club. Every part of the plant is poisonous, from bloom, to stem, to bulb, where the toxin is most concentrated. You have to eat the plant to encounter the worst of its symptoms, including abdominal pain, vomiting, diarrhea and burning of the mouth, lips and tongue. These symptoms typically pass and aren’t usually fatal (the greatest risk is to children who eat bulbs). Cutting buckets of daffodil flowers leads to what’s known in the bulb trade as “daffodil picker’s rash,” a contact dermatitis caused by the pretty bulb’s sap. Gathering a few stems from your garden won’t give you a rash unless you have extremely sensitive skin.

Crown Imperial Fritillaria

Known as the crown imperial, Fritillaria imperialis is an impressive spring bloomer. Tall 3- to 4-foot stems topped with bell-like blossoms command attention. Bulbs boast a skunky scent that repels people and pests alike. It’s a good bulb to plant with tulips to discourage underground critters from feasting on tulip bulbs. A fritillaria bulb contains alkaloids called “imperialin” that are poisonous to people and animals. Eating a large quantity of bulbs is what delivers the fatal blow.

Datura

Also known as thorn-apple (due to its spiky seedpods), Datura is a night-flowering plant with richly perfumed blooms. Flowers are trumpet-shaped, slowly unfurling at dusk and lingering until about noon the following day. When jostled or crushed, leaves release a strong, offensive odor similar to rancid peanut butter. Plants grow quickly and readily self-sow — to the point of becoming invasive. Seeds and flowers are toxic, narcotic and hallucinogenic. Serious illness or death can result from ingesting the plant. Many municipalities forbid growing this potent plant.

Monkshood

For late-season color, it’s tough to beat Aconitum napellus. Also known as monkshood or wolf’s-bane, this pretty perennial opens purple flowers that last through light frosts. All parts of monkshood are poisonous if consumed, especially the roots, which contain aconitine, a heart and nerve poison. Historically, people used aconitum to poison spear and arrow tips for hunting and battle. The poison was a favored execution tool in ancient Rome. The name wolf’s-bane refers to the plant’s ability to repel wolves, both real and werewolves. In 2009, England’s infamous “Curry Killer” used a type of aconitum to kill a former lover. In the garden, wear gloves when handling aconitum to avoid a rash, especially if you have sensitive skin.

Lenten Rose

Early season blooms are the hallmark of Lenten rose (Helleborus), which is sometimes called hellebore or Christmas rose. Leathery evergreen leaves and nodding blooms shine during winter months, with flowers appearing from late winter to early spring. Blossoms unfurl in many hues, including white, pink, burgundy and near-black (like the Dark and Handsome variety seen here). All parts of the plant are poisonous, although roots contain the highest concentrations of harmful compounds, which induce vomiting and can lead to death.

Flowering Tobacco

As the name suggests, flowering tobacco (Nicotiana sylvestris) is one of the plants used to develop the tobacco plant. It’s a warm-weather plant that grows 3 to 5 feet tall. Flowering tobacco opens perfumed white blooms that cascade like exploding fireworks. The flowering tobacco family includes over 60 species, all of which are toxic if ingested because they contain nicotine, which affects nerves controlling heart rhythm. Keep plants away from pets, livestock or curious children who might be tempted to nibble leaves.

Oleander

Beautiful but deadly, oleander is a beloved hedging plant in warm-weather regions and a pretty houseplant in colder zones. Large flower clusters open non-stop from early summer to mid-autumn in many shades, including pink, red, yellow and white. This dense evergreen shrub is intensely poisonous. A single leaf can kill a child, and even honey made from the blooms delivers a non-lethal dose of poison. Red-flowered varieties contain the highest levels of toxic compounds.

Snowdrops

A welcome harbinger of spring, snowdrops (Galanthus) open dainty blooms in early spring, often while snow flurries still dance in the air. These spring flowers contain a nasty compound in their bulbs that, when eaten, leads to dizziness, nausea, diarrhea and, in extreme cases, death. In early spring, people often mistake the strappy leaves of snowdrops for spring onions, pull them up and munch the bulbs. Eating more than three bulbs produces symptoms, but you have to eat a pile of them to induce death.

Chinese Lantern

With its pumpkin-orange seedpods, Chinese lantern (Physalis alkekengi) is the perfect autumn plant. It grows easily, thriving in a sunny spot. Plants are hardy to Zone 6, but readily self-sow, spreading to fill in garden beds (to the point of being invasive, so choose your planting spot with care). Chinese lantern is related to Atropa bella-donna and, like that plant, contains atropine compounds in leaves and seeds. The poison affects people, as well as livestock, and can cause death when eaten.

Japanese Pieris

Japanese pieris (Pieris japonica) earns a place in the landscape for its evergreen nature and late winter-early spring flowers. Also known as lily-of-the-valley shrub, this pretty bloomer packs a deadly punch. All parts of the plant are toxic, containing over 30 different chemicals that affect the heart. Even honey made from the flowers of this shrub is poisonous. The toxins in pieris affect livestock, pets and people. For cattle and goats, the toxic dose is 0.2 percent of the animal’s body weight.