A Complete Guide to Plants Poisonous to Horses

Of every danger lurking in a UK paddock, the plants poisonous to horses are the ones owners most often overlook. Ragwort spreads quietly along hedgerows. Sycamore seeds drift in on autumn wind. Yew clippings tossed over a fence by a well-meaning neighbour can kill a horse within hours. The risk peaks between May and October when grazing is patchy and curious horses sample what they would normally walk past.

This guide covers the most dangerous plants poisonous to horses in the UK and South Africa, how to identify them, the symptoms of poisoning, and what to do if you suspect ingestion. It draws on guidance from the British Horse Society (BHS), World Horse Welfare, the Blue Cross, and the Animal and Plant Health Agency.

Why Horses Eat Plants That Can Kill Them

Healthy horses with abundant grass usually leave toxic plants alone. The smell, taste and texture of ragwort, hemlock and yew are unappealing. Trouble starts when one of four conditions changes that balance.

• Overgrazed pasture. When grass runs short, horses graze closer to fence lines and hedgerows where toxic plants survive in unmown verges.
• Drought or poaching. Dry summers and waterlogged winters thin sward density. Weeds with deep taproots, like ragwort, fill the gap.
• Dried plant material in hay. Cut and baled, ragwort loses its bitter taste but keeps its toxicity. Horses cannot distinguish it from grass once it is in a haylage net.
• Boredom or curiosity. Young horses, ponies on restricted grazing, and stabled animals offered hedge cuttings will sample almost anything.

The British Horse Society estimates that thousands of horses are poisoned by plants each year in the UK, with ragwort and sycamore the two leading causes. Most cases are preventable with active pasture management.

The Most Dangerous Plants Poisonous to Horses in the UK

Eight species account for the overwhelming majority of UK plant poisoning cases. Every owner should be able to identify each one at sight.

Ragwort (Senecio jacobaea)

Tall yellow daisy-like flower with deeply lobed, dark green leaves. Biennial: rosette in year one, flowering stem 30 to 100 cm in year two. Found on roadsides, neglected paddocks and overgrazed fields across the UK.

Ragwort contains pyrrolizidine alkaloids that cause cumulative, irreversible liver damage. There is no antidote. Horses may eat it green if grazing is poor, but the larger risk is dried ragwort in hay, where it loses bitterness but retains full toxicity. Symptoms appear weeks or months after ingestion and include weight loss, jaundice, photosensitisation, and behavioural changes as liver failure progresses. Removal is a legal obligation in some circumstances under the Weeds Act 1959 and the Ragwort Control Act 2003.

Pull ragwort by hand or with a long-handled ragfork before it flowers and wear gloves. The BHS recommends them because the toxins “may be harmful to your skin”, but the claim that the alkaloids absorb through skin goes further than the evidence: the HSE told Defra it had found no experimental data on skin absorption and would expect only a small percentage to pass through intact skin (Defra, 2014). Burn wilted ragwort (in paper sacks, never plastic) or rot small amounts down in a lidded bin away from pasture. The BHS says rotting, not composting, and Defra’s code warns that composting may not kill the seed. Never leave wilted ragwort on the ground where horses can reach it.

Sycamore (Acer pseudoplatanus)

Large deciduous tree with five-lobed leaves and winged paired seeds (helicopters or keys) that spin to the ground in autumn. The young saplings that sprout from those seeds in spring carry the same risk as the seeds themselves.

Sycamore seeds and seedlings contain hypoglycin A, which causes atypical myopathy, also called seasonal pasture myopathy. The toxin destroys muscle fibres including the diaphragm and heart. Mortality is around 75 per cent. Onset is rapid: stiffness, dark coffee-coloured urine (myoglobinuria), reluctance to move, sweating, recumbency, and death within 12 to 72 hours. Outbreaks cluster in autumn (seed fall) and spring (seedlings) on pastures adjacent to sycamores.

In autumn, fence off the areas where sycamore seeds and leaves have fallen, sweep or vacuum seeds where possible, and provide ad-lib hay so horses are not driven to graze fallen seeds out of hunger. Do not rely on a set distance from the tree. An earlier version of this guide said to fence off pasture within 50 metres of a sycamore, and that is not enough: the Royal Veterinary College notes that some helicopter seeds travel up to 200 yards, and the BHS warns that paddocks with no sycamore of their own can still be at risk from blown seed. Horse & Hound’s vet library advises inspecting fields regularly for seeds blown in from nearby trees. The Atypical Myopathy Alert Group, which collects case reports from owners and vets, is run from the University of Liège, and the RVC’s Comparative Neuromuscular Diseases Laboratory tests seeds and seedlings for hypoglycin A.

Yew (Taxus baccata)

Evergreen tree or shrub with flat dark green needles and red berries (the fleshy aril is non-toxic but the seed inside is lethal). Common in churchyards, ornamental hedging and on the edges of country estates.

Every part of the yew except the red berry flesh is highly toxic. A handful of clippings can kill a 500 kg horse within minutes. Toxic alkaloids (taxines) cause sudden cardiac arrest. Horses are often found dead beside the source with no warning signs. There is no antidote; affected horses may collapse before help arrives.

The biggest risk is garden waste tossed into a paddock. Educate neighbours, post signs at field gates, and check fence lines after windy days.

Foxglove (Digitalis purpurea)

Tall biennial with a single flower spike of pink, purple or white tubular bell-shaped flowers. Common in hedgerows, woodland edges and overgrown corners of paddocks.

Contains cardiac glycosides (digitoxin) that disrupt heart rhythm. Symptoms include slow or irregular pulse, weakness, colic and convulsions. Simon Constable’s Equine Vets put the toxic dose at as little as a few hundred grams of fresh flowers, and dried foxglove can be even more potent. Like ragwort, foxglove retains its toxicity in dried form when cut into hay.

Hemlock (Conium maculatum)

Tall (1 to 2 m) biennial with finely divided fern-like leaves, clusters of small white flowers (umbels), and a smooth hollow stem marked with distinctive purple blotches. Strong mousy smell when bruised. Grows on damp ground, ditches and waste land.

Coniine alkaloids cause progressive paralysis, including the muscles of breathing. Symptoms include weakness, dilated pupils, slow pulse, salivation and respiratory failure within hours of eating it. Rutgers Cooperative Extension puts the lethal amount for a horse at about 4 to 5 lb (roughly 2 kg) of the plant.

Deadly Nightshade and Woody Nightshade

Two related species. Deadly nightshade (Atropa belladonna) is a bushy perennial with dull green leaves, bell-shaped purplish flowers and shiny black berries. Woody nightshade (Solanum dulcamara) is a scrambling climber with purple star-shaped flowers and red berries. Both contain tropane alkaloids and solanine that cause dilated pupils, racing heart, colic, drooling and convulsions.

Bracken (Pteridium aquilinum)

Large triangular fronds up to 2 m tall on heath, moorland and woodland edges. Bracken contains thiaminase, an enzyme that destroys vitamin B1. Cumulative ingestion (usually over weeks) causes neurological damage: incoordination, head tremors, weight loss and eventual recumbency. The bladder cancer linked to bracken is recorded predominantly in cattle, and also in sheep (MSD Veterinary Manual); in horses the recognised problem is the thiamine-deficiency syndrome known as bracken staggers. Most common in upland UK grazing and hill pastures in Wales, Scotland and the Lake District.

Buttercups (Ranunculus species)

Bright yellow five-petalled flowers on most UK pastures in late spring and early summer. Fresh buttercups contain protoanemonin, which causes mouth blistering, drooling and mild colic. Horses normally avoid the bitter taste. Buttercups lose their toxicity completely when dried, so they are safe in hay.

Toxic Trees Poisonous to Horses

Trees pose a particular risk because their leaves, seeds, acorns or wilted branches can fall into pasture unnoticed.

• Oak (Quercus). Green acorns, young leaves and oak shoots contain tannic acid and gallotannins. Cause severe colic, bloody diarrhoea, kidney damage. Risk peaks in autumn when acorns drop.
• Cherry, plum and other Prunus species. Wilted leaves release cyanide as they dry. Can kill within minutes. Always rake fallen branches out of paddocks.
• Laburnum (Laburnum anagyroides). Yellow pendulous flowers, seed pods. All parts toxic; seeds especially so. Causes excitement, convulsions, respiratory failure.
• Holly (Ilex aquifolium). Glossy spiky leaves, red berries. Berries cause severe gastroenteritis; horses rarely eat enough to die but the plant should still be fenced off.
• Privet (Ligustrum). Common hedging plant. All parts toxic; causes colic, incoordination, weakness, death in severe cases.
• Box (Buxus sempervirens). Ornamental hedge plant. Causes colic, diarrhoea, respiratory distress.
• Walnut (Juglans). Black walnut shavings used as bedding cause laminitis within 24 hours. Always check bedding source.
• Elderberry (Sambucus nigra). Leaves, bark, roots and unripe berries contain cyanogenic glycosides.

Garden Plants Poisonous to Horses

The most common cause of acute poisoning in stabled horses is garden waste thrown into a field by a neighbour. Familiarise yourself with these ornamentals.

• Rhododendron and azalea. Grayanotoxins cause vomiting (horses physically struggle to vomit, which is itself a clinical emergency), colic, weakness and cardiac collapse. A single mouthful can be fatal.
• Lily of the valley. Cardiac glycosides similar to foxglove.
• Iris. Rhizomes most toxic. Causes drooling, colic, diarrhoea.
• Lupins. Quinolizidine alkaloids cause neurological signs, depression, recumbency.
• Daffodils and other narcissi. Bulbs contain lycorine; cause vomiting, colic, cardiac arrhythmia.
• Hydrangea. Cyanogenic glycosides; causes colic and bloody diarrhoea.
• Wisteria. Seeds and pods cause severe gastroenteritis.

Any hedge trimmings, prunings or lawn cuttings should be composted on the owner’s property, never deposited in a horse paddock. Even small amounts of lawn cuttings are dangerous because horses gulp the soft, sweet material and the fermentation in the gut leads to colic and laminitis.

Poisonous Plants in South African Pastures

South African owners face a different but overlapping list of risks. The Onderstepoort Veterinary Faculty maintains the most authoritative reference; the following are the most common species.

• Tulp (Moraea species). Yellow or orange iris-like flowers in Highveld and Eastern Cape grazing. Cardiac glycosides; rapid death from heart failure.
• Lantana (Lantana camara). Declared invasive shrub with clusters of small multi-coloured flowers. Causes photosensitisation, liver damage, weight loss.
• Senecio (ragwort relatives). Several southern African species contain the same pyrrolizidine alkaloids as UK ragwort. Cumulative liver damage.
• Cestrum (Inkberry). Invasive South American shrub naturalised across SA. Causes liver failure.
• Datura (Stinkblaar). Tropane alkaloids; causes blindness, paralysis, death.
• Bitterappel (Solanum incanum). Yellow berries; cause neurological signs.
• Black wattle (Acacia mearnsii) seedlings. Cyanogenic; risk to young horses on cleared land.

For the veterinary detail, see Botha and Naudé’s Onderstepoort review of plant poisonings of importance in horses in southern Africa (2002). In Highveld and KZN grazing, walk pastures regularly looking for tulp and lantana incursion, especially after summer rains.

Symptoms of Plant Poisoning in Horses

Symptoms vary by the toxin involved, but most plant poisonings present with one or more of the following clinical signs.

• Colic. Pawing, rolling, looking at flanks, sweating, increased heart rate.
• Photosensitisation. Sunburn on pink-skinned areas (muzzle, around eyes, white-haired patches) caused by liver damage, especially with ragwort.
• Jaundice. Yellow tinge to gums and the whites of the eyes.
• Neurological signs. Head pressing, circling, incoordination, head tilt, seizures.
• Respiratory difficulty. Rapid shallow breathing, gasping, blue-tinged gums.
• Discoloured urine. Dark red or coffee-brown urine (myoglobinuria) is a hallmark of atypical myopathy from sycamore.
• Cardiovascular collapse. Weak rapid pulse, cold extremities, recumbency.
• Excessive salivation and oral blistering. Often the first sign with buttercup, hemlock or oleander.

What to Do if Your Horse Eats a Poisonous Plant

Plant poisoning is a veterinary emergency. There is no domestic first aid that will reverse most toxins, and time matters.

1. Remove the horse from the source. Move to a stable or clean paddock immediately. Check what other horses on the same field may also have eaten.
2. Call the vet at once. Describe the plant if you can identify it, the quantity if known, and the time elapsed. Take a sample of the plant if you can do so safely.
3. Do not induce vomiting. Horses cannot vomit. Any attempt is futile and may cause oesophageal damage.
4. Keep the horse calm. Do not exercise. Many plant toxins damage muscle or liver; stress and movement worsen the outcome.
5. Note the symptoms and time of onset. This information helps the vet narrow the differential.
6. Photograph the plant. Even better, bag a sample (roots and all) for laboratory identification.

Treatment depends on the toxin. For most pyrrolizidine alkaloid poisonings (ragwort, senecio) there is no specific antidote and treatment is supportive. For atypical myopathy from sycamore, intensive fluid therapy and intravenous carnitine and vitamins improve survival but case fatality remains high. For yew, treatment is rarely possible because death precedes signs.

Pasture Management to Prevent Poisoning

Prevention is the single most effective strategy. The four pillars of safe pasture management are:

• Walk every field regularly. The BHS lists checking for and removing poisonous plants among its daily checks and routine jobs. Carry a fork and bag. Pull ragwort, hemlock and foxglove before they seed. Re-inspect after storms and high winds when branches fall.
• Maintain sward density. Rest pasture, rotate grazing, top weeds, and reseed bare patches. Healthy grass crowds out toxic invaders.
• Manage hedgerow and tree boundaries. Fence off sycamores, yews, oaks, laburnums and privet so horses cannot reach them or anything that falls from them. No fixed buffer makes a sycamore safe, and the 3-metre buffer this guide once suggested is no protection: seeds can blow up to 200 yards (RVC), so clear fallen seeds and check fields that have no sycamore of their own.
• Source hay carefully. Buy from suppliers who actively control ragwort. Inspect every bale before feeding. Reject any hay with yellow flower heads, dark fern-like fronds, or unfamiliar dried plants.

If you suspect contaminated hay, stop feeding it immediately and contact the supplier. The BHS advises checking forage before feeding, because dried ragwort stays toxic, and buying from trusted suppliers.

Seasonal Poisoning Calendar

The risks shift through the year. Use this calendar to focus weekly inspections.

• March to May. Sycamore seedlings emerge. Bracken unfurls. Garden waste from spring clear-outs appears in fields.
• May to July. Foxglove and ragwort rosettes bolt. Buttercups peak. Lupins, lantana and tulp flower in their respective regions.
• July to September. Ragwort in full flower (and most toxic). Hemlock and nightshade peak. UK summer drought thins grass and pushes horses to graze hedgerows.
• October to November. Sycamore seeds fall. Acorns ripen and drop. Atypical myopathy outbreak season. Garden bonfires increase neighbour-dumped clippings.
• December to February. Yew clippings from Christmas wreaths and garden tidies. Hay quality matters most: a poor bale fed all winter does more damage than a single fresh exposure.

Frequently Asked Questions

What is the most poisonous plant to horses?

Yew is the most acutely lethal: a handful of clippings can kill a 500 kg horse within minutes. Sycamore seeds cause the most fatalities each year through atypical myopathy. Ragwort causes the most chronic deaths through cumulative liver failure.

Can horses eat ferns?

No. Bracken fern (Pteridium aquilinum) is toxic; cumulative ingestion causes neurological damage. Most other ferns are also unsafe. Horses normally avoid them, but in poor grazing they may sample fronds. Fence horses out of fern beds and offer ad-lib hay if pasture is short.

Are buttercups poisonous to horses?

Fresh buttercups are mildly toxic and cause mouth blistering. Most horses avoid the bitter taste. Once dried in hay, buttercups lose their toxicity completely and are safe. For a deeper guide see our article on buttercup poisoning in horses.

How much ragwort is toxic to a horse?

Ragwort is cumulative. A horse eating one or two grams of dried ragwort per kilogram of body weight over several weeks can develop irreversible liver damage. There is no safe dose. The poisoning is silent until liver function drops below 30 per cent, after which symptoms appear suddenly.

Is ivy poisonous to horses?

Common ivy (Hedera helix) contains saponins that cause oral irritation, drooling and mild colic. Most horses avoid it. Sustained ingestion can cause more serious symptoms. Fence off ivy-clad walls and trees where possible.

What trees are poisonous to horses in the UK?

The most dangerous trees in UK paddocks are yew, sycamore (autumn seeds, spring seedlings), oak (acorns and young leaves), cherry and other Prunus species (wilted leaves release cyanide), laburnum, privet, box and walnut. Fence them off where they border grazing, but a fenced strip is no protection from sycamore: its seeds can blow up to 200 yards (RVC), so check the whole field for seeds in autumn and seedlings in spring.

How quickly do poisoning symptoms appear?

It varies. Yew kills within minutes. Atypical myopathy from sycamore can take up to about four days to appear: a European study of 354 cases estimated the latency at up to 4 days (van Galen et al. 2012), so keep watching horses for several days after they come off a risky field. Hemlock and nightshade act within hours. Ragwort and bracken are cumulative and may take weeks or months to show.

For more on field health and prevention, see our guides to laminitis in horses and equine Cushing’s disease. For acute pasture hazards see our article on ticks on horses.