Recently, we were contacted by tenants who believed there to be Giant Hogweed in the communal garden of our property. They were worried, because the sap from this plant can cause severe burns and blindness. We consulted with the Royal Horticultural Society (RHS) at Wisley, who verified that the plant in our grounds was definitely neither Native Hogweed nor Giant Hogweed. However, they identified it as another poisonous plant, Hemlock Water Dropwort.
“Double, double, toil and trouble… root of hemlock… slips of Yew…”
These were all ingredients for the Witches’ brew in Shakespeare’s Macbeth. Fans of the classics will know that when philosopher Socrates was found guilty of heresy, he was sentenced to death by Hemlock poisoning.
Hemlock Water Dropwort was a popular method of execution in Sardinia and is the origin of the phrase ‘Sardonic smile’. The grin deemed so characteristic of Sardinians actually refers to the distinctive facial convulsions caused by Hemlock poisoning.
Should I Be Worried?
Giant Hogweed and Hemlock Water Dropwort are by no means the only native or introduced plants in Britain that are hazardous. Many poisonous plants are common in both gardens and the countryside.
This is not a cause for alarm, since Risk = Likelihood x Severity.
With a few exceptions, most are toxic only if eaten in large quantities – and most poisons are bitter and taste revolting. That is why the plant produces poison – to protect itself by being unappetising. With most of them, poisoning would require perseverence.
Most poisonous plants generally pose more of a threat to livestock, although being smaller, pets and children may be more susceptible to lesser quantities.
How Do I Protect Myself, My Kids & My Pets?
The best protection is to be aware that some plants are poisonous; find out which ones and learn to recognise them. Encourage children and pets not to eat plants and berries. Actions to take if you suspect poisoning are noted at the end of the post.
The RHS has a comprehensive list of Potentially Harmful Garden Plants on its website. There are a lot of them! In this blog, I have highlighted the four most dangerous plants found in the UK. The rest of the list comprises some of the more common poisonous plants, all of which Mark and I have come across in our own garden and surrounding countryside. Knowing this deadly dozen is a start, but be aware that besides some trees and leafy plants, many bulbs, such as daffodils and bluebells are poisonous if eaten, particularly to pets, as are rhododendrons and many species of fungi.
Before you get out the weedkiller, note that there is another side of the coin with these plants. Some are benficial to wildlife and in controlled dosages, the biologically active compounds that they contain have brought huge benefits to modern medicine!
1. Giant Hogweed – Heracleum mantegazzianum
Giant Hogweed is related to the innocuous cow parsley, but is a very nasty plant. If you ever suspect that you have found Giant Hogweed, stay well away and do not touch it. The sap from this plant can cause severe burns and blisters, and can blind you if it gets into your eyes. There are several species of Native Hogweed, all of which can cause rashes, but not as severe as those caused by Giant Hogweed.
Danger – Touch
2. Hemlock Water Dropwort & Hemlock – Oenanthe crocata & Conium maculatum
Hemlock Water Dropwort has been referred to as the UK’s most poisonous indigenous plant. It is also very common and does not pose a risk unless you eat it. All parts of the plant are poisonous, but the roots are the most toxic. Often referred to as ‘dead man’s fingers’, they resemble a bunch of white carrots.
If you forage, it poses a danger because it resembles several edible plants such as Cow Parsley (Wild Chervil). It is a relative of celery, parsley, parsnips and carrots, but also the poisonous Hemlock (Conium maculatum) and Cowbane (Cicuta virosa). The roots are sometimes exposed on river banks or washed up after floods, so be wary when walking your dog.
Danger – Ingestion (Can be fatal)
3. Deadly Nightshade (Belladonna) – Atropa belladonna
One of the deadliest plants, particularly the roots, it contains a variety of toxic alkaloids. It can even be dangerous to touch if you have open wounds. The consumption of a single leaf can be sufficient to kill an adult. The shiny berries can look attractive to children, but eating just one or two can kill. In Italian, bella donna means ‘beautiful woman’ because eye drops made from the plant contain Atropine, which dilates the pupils. This was seen to make the lady more attractive, but is now more applicable in opthamology! Extracts from the plant are widely used in medicine.
Deadly Nightshade is a relative of many edible plants, such as potato, tomato and pepper to name a few. Apart from the edible fruits or tubers, the plants themselves (leaves and stems) are toxic, so if you grow these crops in your garden, make sure that pets don’t stop for a nibble.
Green tomatoes are fine, but a green or sprouting potato is in the process of turning itself into leaves and stems, so it contains higher concentrations of the nerve toxin Solanine. Solanine causes stomach upsets in small quantities or paralysis in very high amounts.
Macbeth used belladonna to kill the Danish army during a truce. One one campsite, we found Deadly Nightshade in the hedge surrounding the dog-walking area and reported it to the warden.
Danger – Touch (with open wounds) & Ingestion (Can be fatal)
4. Wolfsbane (Monkshood) – Aconitum
Wolfsbane covers around 250 species of Aconitum, and gets its name because it was used as a poison to kill wolves. It is sometimes also known as Monkshood or the Devil’s Helmet because of the hood shape of the purple flowers. Every part of the plant is highly poisonous if eaten and the toxins can be absorbed through the skin. Wolfsbane acts quickly and there is no specific antidote.
Cleopatra used Wolfsbane to kill her younger brother – and it allegedly also repels werewolves!
Danger – Touch & Ingestion (Can be fatal)
5. Foxgloves & Lily of the Valley – Digitalis & Convallaria majalis
There are around 20 species of Foxglove; Digitalis purpurea is the Common Foxglove. The name, Digitalis, comes from the shape of the flower, which resembles a thimble that could fit over your digit. All parts of a foxglove plant are poisonous and possibly deadly if swallowed. The heart medicine Digitalis is derived from Foxgloves. Lily of the Valley contains a similar poison and poses the same risks.
Danger – Ingestion (Can be fatal)
6. Lupins – Lupinus
Primarily toxic to animals; they can be fatal to pets. Lupins cause severe discomfort to humans if ingested. The highest concentration of toxin is in the seeds.
Danger – Ingestion
7. Ragwort – Jacobaea vulgaris or Senecio jacobaea
Ragwort causes liver damage and is mildly poisonous to humans. The greatest risk is to grazing livestock and its cumulative effect can be deadly. In my horse riding days, two Shetland ponies at my local stable died because somone tipped grass clippings containing Ragwort into their field. (Grass clippings of any kind should never be given to horses, because they can cause colic.)
Because of the danger to livestock, provisions in The Weeds Act 1959 and the Ragwort Control Act 2003 can order a landowner to control the spread of Ragwort on their land. The Code of Practice on How To Prevent The Spread of Ragwort acknowledges that if kept separate from grazing animals and fodder production, Ragwort is good for biodiversity. It is a useful food plant for many invertabrates, including bees, butterflies and the black-and-red cinnabar moth.
Danger – Ingestion
8. Mistletoe – Viscum album
There are many types of mistltoe; Viscum album is the European variety. The leaves and berries contain the highest concentration of toxins and are dangerous to children and pets if ingested. The greatest risk is at Christmas when this poisonous plant is brought in to the home. Just don’t eat it with your Christmas pud!
Mistletoe got its name because our ancestors noticed that this parasitic plant grows on branches where birds have had a poo. In Anglo-Saxon, ‘mistel’ means dung and ‘tan’ means twig.
For centuries, Mistletoe has been revered as a mythical plant; a sign of friendship in Norse mythology and herbal cure-all in folk medicine. In modern medicine, Mistletoe extracts have been shown to be effective in the treatment of certain cancers, while its use in the treatment of AIDS is under investigation. Other suggested applications are in the control of rheumatism, anxiety, migraine, dizziness, high blood pressure, spasms, asthma, rapid heartbeat, diarrhea, hysteria and amenorrhea.
Danger – Ingestion
9. Laburnum – Laburnum anagyroides
All parts of the plant contain the alkaloid Cystine and are poisonous, especially the seed pods. The toxin is more dangerous to children or pets. Do not let your dog chew laburnum bark or twigs and don’t grow it over ponds. Forsythia, which looks similar to Laburnum, is not poisonous.
Danger – Ingestion
10. Yew – Taxus baccata
The berries and foliage contain various alkaloids and are poisonous if ingested. Apparently dead branches also contain high levels of toxin, so don’t use Yew as throwing sticks for your dog.
Besides being poisonous, evergreen Yew is one of the longest-lived trees in Northern Europe. Possibly the oldest tree in Britain, The Fortingall Yew in Perthshire, Scotland, is estimated to be between two- and three-thousand years old. Branches of old Yew trees can re-root when they touch the ground, so it is unsurprising that it symbolised death and resurrection in ancient Celtic and Druidic cultures. You will often see Yew trees in churchyards, although the reasons behind this are not fully understood. This article gives a few suggestions.
The famous and much feared English longbows were crafted from a single piece of Yew. Yew is light and strong, but particularly suited to bow making because the heartwood and sapwood have different elastic properties and form a natural laminate. (All other wooden bows require layers of wood with different elasticity to be glued together.) When you draw a bow, the front stretches and the back compresses, so you cut your Yew bow stave with the dark, outer sapwood (good at stretching) to the front and the white, inner sapwood (good at compression) to the back.
Danger – Ingestion (and being shot by an arrow…)
11. Rhubarb Leaves & Elephant Ears – Rheum rhabarbarum & Colocasia
Do not eat rhubarb leaves as they can cause kidney failure if eaten in large quantities. They contain much higher concentrations of oxalic acid than the edible stems. The leaves of Colocasia (Elephant Ears) also contain oxalic acid. The tubers of some Colocasia species are a staple food in certain parts of the world, but require extensive processing before they can be eaten safely.
Rhababarum means ‘root of the barbarians.’ To the Romans, anyone who ate Rhubarb was a barbarian!
Danger – Ingestion
12. Cuckoo Pint (Lords & Ladies)
All parts of the plant can irritate the skin, but the berries, which start green and turn bright orange, are poisonous if ingested. They cause inflammation of the throat and breathing difficulties.
Danger – Ingestion
How to Keep Pets & People Safe from Poisonous Plants
- Avoid poisonous plants where possible; keep children and pets away.
- Discourage children & pets from eating any unknown plants or colourful berries.
- Wear gloves when gardening.
- Wash your hands & avoid touching your face anyway – but especially if you think you have had contact with a poisonous plant.
- Do not induce vomiting or give any home remedies such as milk if you suspect that a poison has been ingested.
- Seek medical advice immediately and take along a sample of as much of the plant as possible to aid identification e.g. leaves, stems, flowers, berries, roots.
- Take care when foraging, since some edible and poisonous species are very similar to each other. I read one report where a group of Scottish campers were poisoned by a Hemlock curry, which they had believed to be wild parsnips.
- Don’t put weeds in the compost, particularly not poisonous weeds. Dispose of them responsibly, e.g. on the bonfire.
- Don’t throw dead Yew or Laburnum branches for your dog – and don’t let them chew them.
Although many plants commonly found in gardens and the countryside can be toxic, with sensible precautions, the risks are not high.
- With the exceptions of Giant Hogweed, Deadly Nightshade and Wolfsbane, which can be hazardous to touch, the other plants are dangerous only if eaten.
- Of those, most need to be ingested in large quantities – and the majority taste horrible.
Nevertheless, it is wise to exercise caution with children and pets.
And finally, you will be pleased to know that the Rod Plant, which shot spores into Spock’s face on Star Trek is fictitious!
The list is not exhaustive and is not intended to offer advice but simply to help inform. Please see my Disclaimer for more details.