Take a macabre walk through the poison garden in your own backyard.  Tour the toxic flora of some of the most common garden plants and wild weeds and explore these toxic herbs’  less virtuous attributes.

They say “the poison is in the dose.”

This may be true of a great many toxic herbs, But, some plants just choose violence.

Herbalists seek out plant knowledge. And in doing so we open the gates to a garden of powerful botanicals that ease, relieve, heal… and even hurt. A walk through a garden with me, or, dare I say, just about any herbalist as we seem to all be cut from a similar cloth, is equivalent to inviting a chatty encyclopedia to spew random unsolicited history, tradition, and scientific facts.  Whether you want to or not, you’re probably going to learn something.

Recently, I was having a lovely chat with a dear friend as he drove me to the airport.  I spotted a variety of medicinals along the roadside and was rather absently mentioning them as we passed.  I spotted a rather impressive ditch of water hemlock and pointed it out as “big poison” which led him into telling me about how a certain weed contaminated a relative’s hay harvest, killing several cattle as a result.  This weed had dark, almost black berries, and he had just identified it in his own garden.  

Our ensuing conversation went something like this…

“Ahhh, that sounds like belladonna, also known as deadly nightshade,” I said, following up with perhaps too many details about the toxic aspects of belladonna and a few historical facts about its alleged medicinal use.  You know, as one does.

“Remind me not to cross you,” was his abbreviated reply.

No worries friends, I only use my plant skills for good.

Toxic Herbs & a Little History

However, this left me again pondering the idea of the poison garden (again, as one does).  The most famous  of which is the Alnwick Garden in Northumberland, England, while others can be found in various gardens and exhibitions in Europe and North America.  These curated poison gardens are a nod to apothecary gardens of bygone eras where some of these these toxic herbs were utilized by careful and discerning practitioners for non-nefarious medicinal purposes, but also may take inspiration for the storied 16th century alleged poison gardens of Catherine de Medici, wife of King Henry II of France.

For all practical purposes, the de Medici garden was just your average high ranking nobility apothecary garden, but the Italian and Catholic Catherine was not well regarded by the French peoples and her gardens have long been associated with more sinister intent — a poison garden.  Upon marriage, Catherine influenced French culture with Italian cooking, architecture, beauty practices, perfumery, and medicinal herbs, but she was perhaps more widely known from her commanding and duplicitous nature. She has long been suspected of poisoning her son-in-law’s mother with poison laced gloves. A popular gift signifying gratitude and appreciation amongst nobility, sweet gloves, as they are known at the time, were infused with aromatic botanicals to mask the odor produced during the leather tanning process.  Now largely discredited by modern historians, the Catholic Catherine was rumored to have poisoned the adversarial Protestant Jeanne d’Albret, Queen of Navarre, in a bid to gain more power and influence over the region (“fremeny” much Cathy?).  But I digress – powerful, ambitious, and capable women, good natured or not, with a sense of the use of herbs, have long been associated with nefarious intentions, witchcraft, and occult practices.  

Poison Garden Botanicals

History and highly curated poison gardens aside, learning to identify the potential harmful, toxic, and even lethal plants in our own landscape is important as learning about the more virtuous, healing aspects of herbs so as to avoid possible misidentification, misuse, and unintended contact.  These posion garden specimins span rangy, weedy plants that readily volunteer anywhere their seeds land to stunning lanscape ornamentals observed in many neighborhoods.  A great many of these toxic herbs were, at a time, used for medicinal purposes but have fallen out of the herbal pharmacopeia in favor of milder, safer, more effective herbs. Others have been used to create powerful pharmaceuticals.  Under no circumstances should the toxic herbs in this post be used by a home practitioner.  We simply have safer herbs that foster more favorable outcomes.  As a side note, we are exploring the toxicity of these botanicals as they relate to human exposure, but be aware that these plants are often also toxic to pets, wildlife and livestock as well.  

So with that being said, let’s take a stroll through the poison garden in your own backyard!

Foxglove (Digitalis purpurpea, lanata)
Botanical Family: Plantaginaceae

In bygone years this charming cottage garden staple was used for the treatment of headaches, skin eruptions, diarrhea, epilepsy, and ulcers. Foxglove is a posion garden member, as it is highly toxic and can result in delirium and death if foxglove is ingested.
Toxic parts: all parts
Means of toxicity: ingestion
Primary toxin(s): digoxin

Jimsonweed/moonflower (Datura species)
Botanical Family: Solanaceae

Datura has been used historically to address inflammation, pain, intestinal parasites and digestive issues.  However this poison garden botanical is highly hallucinogenic (and has been used ceremonially by various cultures), and consumption of datura can result in delirium, confusion, acute respiratory depression, extremely high fevers and even death.
Toxic parts: all parts, especially seeds and foliage
Means of toxicity: ingestion
Primary toxin(s): atropine, hyoscyamine, scopalamine

Deadly Nightshade (Atropa belladonna)
Botanical Family: Solanaceae

In the past, belladonna was used internally to relieve spasmodic conditions such as cramping, tension headache, coughing and sneezing, and tremors, and was even dropped into the eye to dilate pupils to “enhance” beauty (as was the fashion of the time).  Deadly nightshade and its botanical cousins can be found in areas of disturbed soils such as roadsides, pastures and gardens. As a powerful nervous system depressant, belladonna is a neurotoxin that significantly inhibits the parasympathetic nervous system resulting in extreme sedation and even death when consumed at moderate doses. (NOTE: belladonna is a popular homeopathic remedy where minute doses are used)
Toxic parts: all parts, especially dark purple berries
Means of toxicity: ingestion
Primary toxin(s): atropine, hyoscyamine, scopalamine

Cherry Laurel (Prunus laurocerasus)
Botanical Family: Rosaceae

Not to be confused with bay laurel, this popular hedge shrub/tree is highly toxic in high enough doses.  Consumption of cherry laurel can result in abdominal pain, vomiting, diarrhea, slowed respiration, dizziness, unconsciousness and death. It is important to note that while this plant is highly toxic, it does take a fairly large amount of this botanical to produce the aforementioned symptoms.
Toxic parts: all parts
Means of toxicity: ingestion (sap may be irritating externally)
Primary toxin(s): cyanide

Rhododendron (Rhododendron species)
Botanical Family: Ericaceae

A favorite of shady gardens, producing colorful blooms in shades of pink, purple, red, and yellow, has some suggestion of medicinal use for inflammation, dysentery, and asthma. However, rhododendron consumption can cause irregular heartbeat and dangerously low blood pressure.  Honey produced from the nectar of rhododendrons has been referred to as “mad honey” and can produce dizziness and confusion if consumed.
Toxic Parts: all parts
Means of Toxicity: consumption
Primary toxin(s): andromedotoxin

Lily of the Valley (Convallaria majalis)
Botanical Family: Asparagaceae

This dainty spring blooming bulb has some associated use for addressing heart conditions and irregular heartbeat, but is moreso known as a lovely but highly toxic botanical.  Lily of the valley poisoning can result in blurred vision, arrhythmia, extreme gastrointestinal pain, and death.
Toxic parts: All parts
Means of toxicity: ingestion
Primary toxin(s): convallarin, convallamarin

Hemlock (Conium maculatum)
Botanical Family: Apiaceae

Although there are some suggestions of ancient Greek and middle Eastern physicians using hemlock for its antispasmodic properties, hemlock is perhaps one for the single most poisonous botanicals known.  This deadly (yet ethereally beautiful, often growing in drainage ditches and damp areas) plant can cause extraordinary nervous system depression, as well as acute renal and cardiac failure at even low doses and exposures.
Toxic parts: all parts; even “dead” canes can be toxic for up to three years.
Means of toxicity: ingestion, although exposure to the juices of hemlock can cause dermatitis and in extreme cases, topical contact could result in toxic constituents entering the bloodstream.
Primary toxin(s): coniine, N-methyl-coniine, conhydrine, psuedoconhydrine, gamma-conicein

Yew (Taxus baccata)
Botanical Family: Taxaceae

This gorgeous evergreen dotted with ruby colored berries in the winter is a popular hedge and focal point planting.  The fleshy parts of the berry have been used historically speaking for arthritis and urinary complaints, as well as headache, but other parts of this plant are considered highly toxic.  Yew can cause confusion, difficulty breathing, irregular heartbeat, convulsions, and coma.  
Toxic parts: bark, needles, seeds (berry flesh is notably less toxic but best to avoid)
Mean of toxicity: ingestion
Primary toxin(s): taxine, taxol

Hellebore (Helleboous x hybridus)
Botanical Family: Ranunculaceae

This stunning shade loving perennial also known as the Christmas or Lenten rose due to its winter blooming period, has been used in the past to address intestinal parasites, gout, and high blood pressure.  That being said, it was also used to poison the tips of arrows.  Hellebores can cause acute gastric distress, lethargy, weakness, reduced heartbeat, and extremely low blood pressure.  Hellebore has a burning acrid taste, and the etymology of the name derives from the Greek word “helien” meaning to injure and “bore” meaning food – suggesting a plant that injures if consumed.  
Toxic parts: leaves, stems, roots
Means of toxicity: ingestion
Primary toxin(s): helleborin, hellebrin, helleborigenin

Castor Bean (Ricinus communis)
Botanical Family: Euphorbiaceae

Castor oil is a much heralded treatment for matters of inflammation and discomfort, to promote healing of both acute and chronic conditions. Native to tropical Africa, the castor bean has naturalized to similar habitats throughout the world, including tropical parts of the US such as the US Virgin Islands and Puerto Rico where it can be found in moist places such as drainage ditches and riverbanks.  While most of the plant is largely harmless and even highly medicinal in the case of the oil produced from the beans, the bean hull contains the deadly poison ricin giving this toxic herb its righful spot in the poison garden.  If ingested ricin can cause severe vomiting, dehydration, renal and liver failure, while inhalation can cause pulmonary edema and respiratory failure, and death.
Toxic Parts: hull
Means of toxicity: ingestion, inhalation
Primary toxin(s): ricin

Tansy (Tanacetum vulgare)
Botanical Family: Asteraceae

This sunny yellow botanical found in grasslands, pastures and areas of disturbed soil has been used for remedy fevers, induce sweating, encourage bowel movements, and soothe acne.  However, tansy is toxic and can induce severe diarrhea, intestinal bleeding, depress the central nervous system, and cause liver damage or failure.  It is also highly toxic to grazing livestock and ruminant animals.
Toxic parts: all parts (especially at the time of flowering
Means of toxicity: ingestion, some speculation suggests that some toxins are absorbed through the skin too
Primary toxin(s): pyrollizidine

Wisteria (Wisteria frutascens)
Botanical Family: Fabaceae

A stunning beauty of ill repute, wisteria’s weeping nature and lilac blooms hide its aggressive growth habitat which can out compete native plants and wreak havoc on structures.  Wisteria has some use in traditional Chinese Medicine for the treatment of various cancers and rheumatoid arthritis, but the seed pods are considered toxic. Ingestion of wisteria seeds and pods can produce severe stomach upset, vomiting, and an oral burning sensation making it a beautiful but destructive member of the poison garden.
Toxic parts: all parts, but the seeds and pods are highly toxic
Mean of toxicity: ingestion
Primary toxin(s): lectin, wisterin

Giant Hogweed (Heracleum mantegazzianum)
Botanical Family: Apiaceae

This towering and downright impressive cousin of water hemlock grows in moist places with disturbed soil.  Other than being rather dangerously beautiful with its staggering size and lacy white flowers, my research sheds no real redeeming characteristics for this particularly nasty poison garden botanical.  Contact with the sap causes severe photosensitivity on the skin, resulting in painful large blisters and rashes.  This photosensitivity can last days after exposure and cleansing of skin.  Giant hogweed should also not be confused with other edible plants bearing the common name “hogweed.” 
Toxic parts: all parts, especially the sap
Means of toxicity: topical exposure, ingestion
Primary toxin(s): furanocoumarins

Delphinium (Delphinium elatum)
Botanical Family: Ranunculaceae

This beautiful cottage garden staple, blooming in tall spikes of often blue-ish flowers, has been used historically for asthma, insomnia, fluid retention, and intestinal parasites.  However delphiniums, also called larkspur, have deleterious effects on the neuromuscular system and can cause lack of coordination, paralysis and death and there is no known effective treatment to reverse severe delphinium poisoning. 
Toxic Parts: all parts, especially new growth and seeds
Means of toxicity: ingestion
Primary toxin(s): methyllycaconitine

Mandrake (Mandragora officinarum)
Botanical Family: Solanaceae

With its roots having a resemblance to the human body, mandrakes have fit their way into many fantastical stories.  Mandrake has also been used historically to address insomnia and pain, and was even thought to increase libido.  With that said, this quirky botanical is a powerful hallucinogen and narcotic, acting on the central nervous system.  Mandrake can produce visual disturbances, profuse sweating and overheating of the body, confusion, and, in large enough doses, even death.
Toxic Parts: all parts
Means of toxicity: ingestion
Primary toxin(s): atropine, hyoscine, scopolamine

Henbane (Hyoscyamus niger)
Botanical Family: Solanaceae

In older times, henbane actually was used to relieve pain (especially bone discomfort), toothache, asthma, tremors, and digestive cramping.  Henbane can be found in dry, sandy soils, often in open fields and previously cultivated land.  Largely associated with witchcraft and its use in “flying ointments”, henbane is a profound hallucinogen producing delirium, intoxication, heart palpitations, and even coma or death. 
Toxic parts:  leaves, seeds, roots
Means of toxicity: Ingestion, skin contact
Primary toxin(s): atropine, hyoscyamine, scopolamine, tropane

Golden Chain Tree (Laburnum anagyroides, alpinum)
Botanical Family: Fabaceae

This beautiful ornamental tree dripping with lovely yellow spring flowers, was once used to induce vomiting, reduce constipation, and relieve whooping cough.  But, as the other botanicals on this list, the golder chain tree is a highly toxic herb.  Symptoms of golden chain tree toxicity include unequally dilated pupils, frothing of the mouth, lethargy, coma, and death.
Toxic parts: all parts, especially seeds
Mean of toxicity: ingestion
Primary toxin(s): cytisine

Angel’s Trumpet (Brugmansia species)
Botanical Family: Solanaceae

Angel’s trumpet is a truly impressive ornamental with past suggestion of use for pain and inflammation.  It is also steeped in lore of magic and ceremony, largely owing to its hallucenogenic properties.  This toxic herb can induce rapid heartrate, hyperthermia, confusion, seizures and death.
Toxic parts: all parts, especially the seeds
Means of toxicity: ingestion
Primary toxin(s): atropine, hyoscyamine, scopolamine

Monkshood/Wolfbane ( Aconitum napellus)
Botanical Family: Ranunculaceae
Herbalists of yore may have used monkshood to relieve joint pain, reduce fevers, and slow an elevated heart rate.  This toxic herb can induce vomiting, nausea, and is considered a cardiac and neuro toxin.  Monkshood tends to grow in damp areas such as by streams and ponds.
Toxic parts: all parts
Means of toxicity, ingestion, skin contact (all though this type of exposure does not pose as great of a potential risk)
Primary toxin: aconitine, mesaconitine

Lupine (Lupinus perennis)
Botanical Family: Fabaceae

A stunning wild and cultivated flower that enjoys rocky lean soils, lupine has been used in the past to address urinary tract complaints.  Lupine can cause severe stomach upset, vomiting, diarrhea, confusion and dizziness.
Toxic parts: all parts, especially new spring growth and seed pods
Means of Toxicity: ingestion
Primary toxin(s): lupinine, piperidine, quinolizidine

Caladium (Caladium species)
Botanical Family: Araceae

Caladiums bear striking foliage and are a highly popular potted plant.  It also has been used in the past to soothe external wounds and boils.  This toxic herb can cause a burning sensation in the mouth, excessive salivation, blistering about the mouth, vocal changes, and is known to be extremely irritating to the eye.
Toxic Parts: all parts
Means of Toxicity: Ingestion, eye contact
Primary toxin(s): calcium oxalate, asparagine

Lantana (Lantana camara)
Botanical Family: Verbenaceae

Lantana boosts brightly colored blooms and is a favorite of container gardens for a vibrant summer show.  This botanical has been used to address high blood pressure, cough, infection and rheumatism.  However, lantana is a mildly toxic herb that can cause vomiting, diarrhea, breathing difficulties, and liver damage (in excessive dosage).
Toxic parts: all parts
Means of Toxicity: ingestion, skin contact (mild irritant)
Primary Toxins: latadene A and B

Rhubarb (Rheum rhabaranum)
Botanical Family: Polygonaceae

Rhubarb stems are one of the very first harvests that gardeners can enjoy each spring.  While we may enjoy turning the ruby hued stalks into jams, pies and even delicious bar cookies, the stalks and roots are used in Traditional Chinese Medicine to relieve oral sores and inflammation.  However the goodness stops at the stalks, as the leaves are a toxic herb that can cause stomach upset, and even kidney stones renal failure in excessive amounts.
Toxic Parts: leaves
Means of toxicity: ingestion
Primary toxin(s): oxalic acid

Daffodil (Narcissus pseudonarcissus)
Plant Family: Amaryllidaceae

This sunny bulb emerges in late winter to usher in the warmer and longer days ahead.  There is some suggestion that the daffodil has been used for spasmodic coughs and congestion, but daffodils should be considered a toxic herb. Daffodils can cause severe nausea, vomiting, diarrhea, and sores about the mouth.
Toxic parts: all parts, especially the bulb
Means of toxicity: ingestion
Primary toxin(s): lycorine

Oleander (Nerium oleander)
Botanical Family: Apocynaceae

This stunning shrub is a landscape ornamental in warmer temperate and subtropical zones.  There is some evidence of oleander being used for skin related maladies, cancer, diabetes, asthma and heart disease, but is largely regarded as a highly toxic herb making it one of the dealiest of the poison garden. Symptoms of oleander toxicity include digestive upset, lethargy and dizziness, but is most commonly regarded as a powerful cardiac toxin producing blood pressure issues, disruption in electrolyte balance, with possible coma and death.
Toxic parts: all parts
Means of toxicity: ingestion, skin contact (sap), inhalation (if burned)
Primary toxin(s): digitoxigenin, folinerin, neriin, oleandrin, rosgenin

Azalea (Rhododenderon indicum, molle)
Botanical Family: Ericaceae

This pretty, often petite shrub with flowers in a great variety of shades is at home in a woodland landscape.  Azalea flowers have been used as a topical anesthetic and sedative, while the roots have been used for the treatment of arthritis and rheumatism in Traditional Chinese Medicine.  With that being said azaleas should be a highly toxic herb, producing arrhythmia, low blood pressure, and sense of intoxication.
Toxic parts: all parts
Means of toxicity: ingestion
Primary toxin(s): andromedotoxin