The foundation of equine health lies in creating a horse-friendly environment and using high-quality pasture. Meadows and fields are not only grazing grounds but they provide essential living space for horses and form the basis of their entire diet. But these pastures don’t just grow beneficial grasses and herbs. Sometimes, they also harbour poisonous plants that can present serious risks.
These so-called toxic plants for horses can trigger a wide range of symptoms, from digestive problems and swelling to skin irritation, and in the worst cases, even death. While some are easy to recognize, many toxic species blend in with harmless plants or look deceptively beautiful.
Today, there are approximately 80 genera of plants in Central Europe (not counting individual species) that are known to be dangerous plants for horses. It is therefore essential that you become familiar with both the names and visual characteristics of these plants, so you can detect them early and protect your horse from accidental contact or ingestion.
Poisonous plant guide for horses
To support you in identifying these threats, we’ve created a detailed toxic plant guide. It’s available to download, print, and use as a reference directly in your stable. Most of the entries come with photographs to help you visually distinguish harmful plants from harmless ones.
Tip: Print the list and keep it accessible next to your feed room or tack cabinet so you can consult it whenever needed.
Why horses sometimes eat poisonous plants
Most poisonous plants horses encounter contain bitter substances (so-called secondary metabolites) that discourage grazing through their unpleasant taste. In many cases, horses instinctively avoid these plants. Their sense of taste acts as a first line of defence.
But you should never rely solely on this instinct. Several toxic plants lose their bitterness after drying (for example, in hay or silage), while others only develop their bitter taste at full maturity. Some plants may even appear in partial or damaged form, such as a single snapped stem, which can still pose a serious risk.
What’s more, horses react far more sensitively to plant toxins than many other animals. Even small traces of certain substances can be enough to trigger visible poisoning symptoms. Therefore, it’s not just about avoiding large amounts but it’s about avoiding any contact at all.
What exactly is plant poison?
When we speak of plant toxins, we’re referring to natural compounds within certain plants that become harmful when consumed. The severity of poisoning depends primarily on the concentration of these substances in the plant. And that concentration isn’t static but it can vary widely depending on:
- Weather conditions
- Growth phase
- Sunlight exposure
- Soil nutrients and pH
- Fertilization practices
Plant toxins fall into several chemical categories, including:
- Alkaloids (such as aconitine, atropine, taxine)
- Enzymes (which interfere with the metabolism)
- Saponins, terpenes, terpenoids, and oxalic acid
- Nitrates and plant-based hormones
Even if a plant looks harmless at first glance, its chemical profile can be highly toxic under the surface.
Common poisonous plants for horses in the UK
Bracken fern (Pteridium aquilinum)
Bracken fern is a common sight in many wooded regions of Central Europe, often growing in sunny forest clearings and along woodland edges. Though it may seem innocuous, this fern poses a significant risk to horses due to its content of thiaminase and cyanogenic glycosides. These compounds break down thiamine (vitamin B1) in the horse’s body, which is essential for proper nerve function.
The result of long-term ingestion is a vitamin B1 deficiency that can cause neurological disorders, muscle coordination problems, and eventually ataxia. In some studies, glycosides present in bracken fern have also been associated with carcinogenic effects. Horses are unlikely to eat bracken in the wild unless grazing is poor, but dried fern mixed in hay presents a real and often overlooked danger, especially if hay is sourced from pasture edges or neglected fields.
Symptoms:
- Ataxia (loss of coordination)
- Muscle tremors and weakness
- Lethargy
- Nervous system dysfunction
Toxic dose:
- Approx. 2 kg per day over 30 days is enough to cause serious illness or death
Sycamore maple (Acer pseudoplatanus)
The sycamore maple is widespread and poses a particularly high risk to grazing horses, especially in spring and autumn. The seeds (so-called „helicopters“) and young seedlings contain a toxin called hypoglycin A, which has been linked to atypical pasture myopathy (APM). This condition attacks the horse’s skeletal and heart muscles and is often fatal, even with intensive treatment.
The problem arises when sycamore trees border or stand inside horse pastures. Wind and rain can scatter seeds across grazing areas, and new sprouts blend in easily with regular grasses. Horses, especially young or distracted ones, may consume them without hesitation, especially when grazing is sparse. A single ingestion event can be enough to cause life-threatening symptoms within hours.
Symptoms:
- Heavy sweating
- Muscle tremors and stiffness
- Colic-like pain
- General weakness or sudden collapse
- Dark-colored urine due to muscle breakdown
Toxic dose:
- As few as 165 seeds, or 500 g of leaves
- Even small quantities of seedlings may be fatal
Monkshood (Aconitum napellus)
Monkshood, also known as blue aconite or wolfsbane, is strikingly beautiful, and extremely dangerous. Considered the most poisonous plant in Central Europe, it contains the deadly alkaloid aconitine, which disrupts nerve impulses and heart rhythm. All parts of the plant are toxic, even when dried.
Monkshood is sometimes planted in decorative gardens or borders due to its deep blue blossoms. But it also grows wild on moist pastures, especially in mountainous regions. If even a small amount makes its way into hay or is grazed, the consequences can be swift and devastating.
Symptoms:
- Salivation and restlessness
- Diarrhea and muscle cramps
- Dilated pupils
- Irregular heartbeat
- Paralysis of facial muscles or tongue
- Death through circulatory or respiratory failure
Toxic dose:
- As little as 100-200 g of fresh plant can be fatal
Yew (Taxus baccata)
Yew is a common landscaping shrub, often used in hedges or cemeteries, but it is among the most lethal toxic plants for horses. The plant contains taxine alkaloids, which interfere with the heart’s ability to contract properly, causing rapid death, often without warning symptoms.
All parts of the plant are poisonous: the dark green needles, the bark, the wood, and the seeds inside the red berries (arils). While horses rarely browse live yew, danger arises when hedge trimmings are tossed into pastures or yew branches fall into fields during storms. The dried parts retain their toxicity and are just as deadly.
Symptoms:
- Accelerated heart rate
- Staggering or weakness
- Seizures or muscle spasms
- Foaming at the mouth
- Sudden collapse and death
Toxic dose:
- Only 100-200 g of needles or bark can cause death within minutes
Foxglove (Digitalis purpurea)
Foxglove is an unmistakable plant, known for its tall spires of pink to purple bell-shaped flowers. While beautiful, it is highly toxic to horses. Every part of the plant contains digitalis glycosides, which disrupt the electrical activity of the heart. Even dried leaves retain their toxicity, making foxglove one of the most dangerous poisonous plants horses may ingest unknowingly in hay.
Foxglove is commonly found in mountain meadows, light forests, and also cultivated gardens. Because the symptoms of poisoning set in rapidly and mimic colic or cardiac failure, foxglove ingestion is a veterinary emergency. A relatively small amount is enough to cause arrhythmias or heart failure in even healthy horses.
Symptoms:
- Bloody or watery diarrhea
- Confusion and lethargy
- Irregular or rapid heartbeat
- Muscle weakness
- Seizures or sudden collapse
Toxic dose:
- As little as 25 g dried or 100-200 g fresh leaves can be fatal
Hemlock (Conium maculatum)
Hemlock is often mistaken for harmless plants like wild carrot or cow parsley, making it especially dangerous. It typically grows along roadsides, riverbanks, and uncultivated land. This tall, umbrella-like plant contains the neurotoxin coniine, which causes progressive muscle paralysis. All parts are poisonous, especially the roots and seeds.
Horses rarely graze on hemlock voluntarily, but ingestion may occur when the plant is dried into hay or if forage is scarce. Even small amounts can lead to severe respiratory symptoms and collapse.
Symptoms:
- General muscle weakness
- Tremors and twitching
- Increased pulse
- Dilated pupils
- Respiratory distress or paralysis
Toxic dose:
- Between 3 and 5 kg of fresh plant material can cause death
Laburnum (Laburnum anagyroides)
Also known as golden chain tree, laburnum is a common ornamental shrub or tree found in gardens and public parks. It is easily recognized by its long, hanging yellow blossoms. Unfortunately, this plant contains several toxic alkaloids, most notably cytisine, which remain active even when dried.
All parts of the plant are poisonous, but the seeds and seed pods are especially concentrated in toxins. Horses may be exposed when laburnum trees grow near pastures, or when dried pods are blown in. Children have been poisoned by laburnum as well; its toxicity is not species-specific.
Symptoms:
- Profuse sweating and muscle tremors
- Difficulty breathing
- Rapid heart rate
- Digestive discomfort and colic
- Disorientation or seizures
Toxic dose:
- 250-300 g of seeds can be lethal for an adult horse
Autumn crocus (Colchicum autumnale)
Autumn crocus is a discreet and dangerous plant found mainly in damp pastures and moist meadows. Unlike its spring-blooming cousin, autumn crocus flowers in late summer or fall, often when grazing is still active. It contains the potent alkaloid colchicine, which inhibits cell division and severely damages internal organs. In the UK, it occurs locally, especially in moist grasslands in parts of southern England and Wales.
What makes this plant especially dangerous is that its toxicity persists when dried, making hay contamination a common risk. Even small amounts can trigger symptoms that worsen over several days.
Symptoms:
- Loss of appetite and colic
- Severe salivation and dehydration
- Bloody diarrhea
- Muscle weakness and cramps
- Paralysis and collapse
Toxic dose:
- Between 1.2 and 3 kg of fresh or dried plant material can cause death
Ragwort (Senecio jacobaea)
Ragwort is one of the most dangerous and persistent poisonous plants for horses in the UK. It thrives in nitrogen-rich, compacted soils, especially on overgrazed or poorly maintained pastures. What makes ragwort so dangerous is that it remains toxic even after drying and loses its bitter taste, making it particularly risky in hay and silage.
The plant contains pyrrolizidine alkaloids, which damage the liver irreversibly. Horses may consume small quantities over time without immediate symptoms, leading to chronic poisoning. Unfortunately, once liver failure sets in, treatment options are limited.
Symptoms:
- Lethargy and apathy
- Loss of appetite and weight
- Coordination problems
- Liver damage and jaundice
- Photosensitivity
Toxic dose:
- Ponies: 4 kg fresh or 0.5 kg dried
- Horses: 14 kg fresh or 2 kg dried (consumed over time)
St. John’s Wort (Hypericum perforatum)
In the UK, St John’s wort grows at woodland edges, roadsides, and rough grassland. It contains hypericin, a compound that makes the skin extremely sensitive to UV light. Ingestion followed by sun exposure can cause painful skin reactions, especially in horses with white or pink skin.
Although horses generally avoid it in its fresh state, St. John’s Wort becomes more dangerous when dried in hay, where it’s harder to recognize.
Symptoms:
- Swollen lips and muzzle
- Red, inflamed skin in sun-exposed areas
- Nervous behavior or agitation
- Itching or rubbing against fences
- Avoidance of sunlight
Toxic dose:
- As little as 0.5% of body weight can trigger severe reactions
Black locust (Robinia pseudoacacia)
The black locust tree, also known as false acacia, is prized for its hard, durable wood, and often used in fences, posts, and even stable structures. But all parts of this tree except the flowers contain toxins such as robin and phasin, which are harmful to horses.
Horses may chew on bark, leaves, or pods out of boredom, especially if trees grow near or within their enclosure. Even small fragments ingested from chewed wood or fallen branches can lead to poisoning.
Black locust is not native to the UK but is occasionally planted in parks, gardens, and even near some equestrian properties. It grows well on poor soils and has escaped into the wild in a few areas of southern England.
Symptoms:
- Salivation and restlessness
- Diarrhea or colic
- Tremors and ataxia
- Yellow mucous membranes (jaundice)
- Liver and kidney damage
Toxic dose:
- Even small amounts of bark, pods or leaves may be harmful
Nightshade plants – henbane, belladonna, jimsonweed
Various members of the nightshade family pose a threat to horses in the UK, particularly in abandoned fields, wasteland, or near old stables. The nightshade family includes several extremely toxic plants for horses, such as henbane, deadly nightshade (belladonna), and jimsonweed (datura). They contain tropane alkaloids like atropine and scopolamine, which severely affect the central nervous system.
These plants are dangerous even in tiny amounts. Symptoms can appear suddenly and progress quickly.
Symptoms:
- Dilated pupils and light sensitivity
- Dry mouth and swallowing difficulty
- Muscle spasms and tremors
- Aggression or confusion
- Seizures, paralysis, or respiratory arrest
Toxic dose:
- Varies by species, but even small quantities may be fatal
How to protect your horse from poisonous plants
The best protection against plants that are toxic to horses is vigilance and proactive pasture management. Here’s what you should consistently do:
- Inspect your pastures regularly, especially after storms or seasonal changes.
- Check hay, silage, and bedding carefully for foreign plant material.
- Never allow grazing on unknown fields without walking them thoroughly.
- Remove poisonous plants by the root and dispose of them in sealed bags.
- Wear gloves: Many plant toxins can enter the body through the skin.
- Avoid planting ornamental toxic species near barns, paddocks, or trail routes.
- Repeat pasture checks throughout the year, not just once per season.
- Prevent boredom grazing: Offer sufficient forage and enrichment to avoid plant curiosity.
During trail rides, always monitor your horse closely. Grazing “on the go” can result in accidental ingestion of unfamiliar or exotic toxic plants, especially when the horse is working and less selective.
What to do if your horse has ingested a poisonous plant
Despite all efforts, poisoning accidents can still happen. If you suspect your horse has eaten a poisonous plant, act immediately.
- Call your vet without delay. Time is critical.
- Identify the plant if possible and estimate the amount consumed.
- Describe symptoms clearly: Are there signs of colic, tremors, salivation, restlessness, paralysis?
- Remove the horse from the pasture and provide a calm, shaded space.
- Don’t wait for symptoms to worsen, some toxins act within minutes.
For chronic poisoning, such as from ragwort, symptoms may only appear after long-term exposure. These are harder to diagnose and treat, so prevention is essential.
Keep visual plant references at the barn and educate your team regularly. When in doubt about a plant’s safety, always consult a vet or agricultural expert before allowing access.