Plants Poisonous to Horses: US Field & Emergency Guide

Some of the most dangerous plants poisonous to horses include yew, oleander, water hemlock, poison hemlock, wilted wild cherry leaves, and box elder seeds. Red maple leaves, ragwort, and bracken fern can cause serious blood, liver, or nervous-system damage. If exposure is possible, call an equine veterinarian immediately, even if your horse looks normal.

The Plants Most Dangerous to Horses in US Pastures

Focus on what a plant can do and how a horse might reach it. Not every unfamiliar weed poses the same level of danger:

• Potentially fast and fatal: yew, oleander, water hemlock, poison hemlock, wilted cherry leaves, and some nightshades. Even a small quantity of certain species can be an emergency.
• Serious organ or cumulative damage: ragwort and related weeds can damage the liver; repeated consumption of bracken fern can affect the nervous system. Wilted red maple leaves can damage red blood cells, while black locust and black walnut bedding pose different but serious risks.
• Primarily irritants: fresh buttercup can cause mouth irritation and digestive signs, particularly when a horse eats substantial amounts. It deserves attention, but it doesn’t have the same emergency profile as yew.

Horses often avoid unpalatable plants when good forage is plentiful, but you can’t rely on avoidance. Overgrazing, drought, boredom, new turnout, contaminated hay, fallen branches, and discarded hedge clippings can all lead to exposure.

This guide can help you recognize and reduce the risk, but it doesn’t replace veterinary care or provide a treatment plan.

Toxic plants versus injurious plants like foxtail

A toxic plant causes harm through chemicals; an injurious plant can cause physical damage without a poison. Foxtail seedheads, for example, have sharp awns that can lodge in the mouth and cause sores. Suspected mouth injury still warrants veterinary advice and removal of the offending forage.

Symptoms of Plant Poisoning in Horses: Start From the Sign, Narrow to the Plant

Early signs can include reduced appetite, drooling, colic, depression, and changes in manure or urine. A matching symptom is a lead for your veterinarian, not a diagnosis. Infections, injuries, feed problems, and other illnesses can look similar.

Observed sign	Candidate plants or exposures	Urgency	Other possibilities to mention	What to do now
Sudden collapse or a horse found dead	Yew, oleander, water hemlock, wilted cherry	Call a vet now	Heart disease, trauma, severe colic	Keep other horses away; preserve nearby plant and feed samples.
Tremors, seizures, or agitation	Water hemlock, poison hemlock; other neurologic toxins	Call a vet now	Tetanus, neurologic infection, contaminated feed	Keep people safe and the horse quiet; do not force it to walk.
Colic or abdominal pain	Oleander, oak, nightshade, black locust	Call now for severe pain or other signs; otherwise call promptly	Impaction, gas, sand, grain overload	Remove suspect feed and report manure changes.
Drooling or mouth sores	Fresh buttercup, irritating plants; clover-associated slaframine	Call the same day; sooner with other signs	Dental disease, foxtail awns, chemical irritation	Remove suspect forage; examine the mouth only if safe.
Dark red or brown urine	Wilted red maple; box elder-associated muscle disease	Call a vet now	Muscle injury, urinary or kidney disease	Note the time and photograph the urine if possible.
Stumbling or incoordination	Hemlocks, bracken fern after repeated grazing, nightshades	Call now if sudden; same day if mild	Spinal disease, neurologic infection	Avoid moving a staggering horse without veterinary guidance.
Yellow gums or sunburn on pink skin	Ragwort and related liver-damaging plants; alsike clover	Call the same day; now if the horse is weak or down	Other liver disease or red blood cell damage	Provide shade if safely accessible; save hay and feeding history.
Weight loss, dullness, or changed behavior over weeks	Ragwort, bracken fern, other chronic exposure	Call the same day	Dental problems, parasites, ulcers, chronic disease	Gather pasture, feed, manure, and recent health records.
Hot feet, strong digital pulses, or reluctance to move after new bedding	Black walnut shavings	Call a vet now	Other causes of laminitis, including grain overload	Prevent further bedding contact if safe; keep a sample.

Excessive salivation associated with clover can result from slaframine produced by a fungus on the plant, rather than from the clover alone. Alsike clover has separately been associated with photosensitivity and liver injury.

Sudden signs: collapse, tremors, colic, and dark urine

Treat collapse, seizures, breathing difficulty, severe colic, and dark urine as emergencies, even if you can’t identify a plant. Red maple exposure is one possible explanation for dark urine, but a veterinarian must distinguish it from other serious causes.

Slow signs: weight loss, jaundice, and neurologic changes

Some plant injuries develop through repeated exposure, with signs appearing long after the horse first ate the plant. Tell the vet about previous pastures and hay as well as the current feed. Don’t simply watch indefinitely if a horse is eating poorly, losing weight, or behaving unusually.

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What to Do If Your Horse Eats a Toxic Plant: The First 15 to 60 Minutes

Call immediately; don’t spend the first hour trying to identify the plant. Suspected exposure to yew, oleander, water hemlock, poison hemlock, wilted cherry, or box elder seeds warrants urgent veterinary contact before signs appear.

Who to call, in what order

1. Call your equine veterinarian or emergency backup first. Give your location and say that you suspect poisoning. Follow the vet’s instructions about movement, feed, water, and monitoring.
2. Move the horse away from the source if it can walk safely. Use a secure stall or paddock and keep other horses from reaching the plant. Don’t drag a down horse or force a staggering one to move.
3. Call ASPCA Animal Poison Control at 888-426-4435, particularly if the vet requests toxicology support or the plant is uncertain. A consultation fee may apply. Your veterinarian can also advise whether to contact a state veterinary diagnostic laboratory.
4. Remove suspect hay, feed, clippings, or bedding from access. Keep a labeled sample and separate the affected lot from uncontaminated supplies.
5. Keep the horse calm. Don’t force exercise. Record when exposure may have occurred and when each sign began.
6. Collect information and samples while help is on the way. Do this only if it won’t delay the call or put anyone in danger.

What to collect for the vet or poison control

Photograph the whole plant in its setting, then its leaves, stem, base, and flowers, berries, or seeds. Wear gloves and place a representative sample in a labeled bag; keep suspect hay or bedding separately. Don’t handle a hazardous plant with bare hands or taste it.

Have the horse’s approximate weight, age, pregnancy status if applicable, and medications ready, along with the estimated amount eaten, the plant’s condition—fresh, wilted, or dried—and relevant changes in turnout, storms, feed, or bedding. If the amount or plant is unknown, say so. The vet may recommend an examination and bloodwork or other tests based on the history and signs.

What not to do

Don’t attempt to induce vomiting: horses cannot effectively vomit to clear a toxic meal. Don’t give oil, milk, salt water, activated charcoal, medications, or other home remedies—including beer given to horses—unless your veterinarian directs you to. Don’t wait for symptoms to confirm your suspicion.

How Much Is Too Much? Toxic Doses and Which Plants Kill Fast Versus Slowly

There is no safe dose to test at home. Risk depends on the plant species, part, maturity, season, fresh or wilted condition, and the type and condition of the individual horse. A published toxic quantity isn’t a threshold below which veterinary advice is unnecessary.

The table prioritizes practical exposure routes, not prevalence. High-severity ornamentals may be uncommon in a pasture itself but accessible as hedge trimmings or blown branches. Where a dose description has no number, a reliable general threshold isn’t established here.

Common name	Scientific name	Toxic parts	Primary toxin or agent	Severity	Approximate dose context	Onset	Early signs
Oleander	Nerium oleander	All parts; fresh or dried clippings	Cardiac glycosides, including oleandrin	High	Small amount can be dangerous; no safe threshold	Rapid	Colic, weakness, abnormal heart rhythm
Yew	Taxus spp.	Needles, bark, seeds and clippings	Taxine alkaloids	High	A lethal quantity of leaves has been reported around 0.1% of body weight; highly variable.	Rapid	Trembling, breathing trouble, collapse; signs may be missed
Water hemlock	Cicuta spp.	All parts, especially roots	Cicutoxin	High	As little as about 8 ounces has been reported lethal to a horse; root content and individual risk vary.	Rapid	Drooling, tremors, seizures
Poison hemlock	Conium maculatum	All parts, including seeds	Piperidine alkaloids, including coniine	High	A reported lethal amount is approximately 4–5 pounds for a 1,000-pound animal; this is not a safe-exposure limit.	Rapid	Weakness, incoordination, breathing difficulty
Wild or black cherry	Prunus spp.	Especially wilted leaves on fallen limbs	Cyanogenic glycosides	High	A toxic quantity of black cherry leaves has been reported around 2.5 pounds for a 1,000-pound horse; risk varies.	Rapid	Agitation, breathing difficulty, weakness
Red maple	Acer rubrum	Wilted or dried leaves	Oxidant compounds, including gallic acid	High	Approximately 1.5–3 pounds of wilted leaves has been reported to poison a horse; smaller suspected exposures still merit a call.	Acute to delayed	Weakness, dark urine, yellow gums
Tansy ragwort	Jacobaea vulgaris, formerly Senecio jacobaea	All parts, including dried plants	Pyrrolizidine alkaloids	High cumulative	Repeated consumption can add to liver damage; no safe cumulative allowance	Cumulative	Weight loss, jaundice, abnormal behavior
Bracken fern	Pteridium aquilinum and related species	Fronds and rhizomes	Thiaminase	Moderate to high	Usually associated with repeated consumption; threshold varies	Cumulative	Weight loss, tremors, incoordination
Black locust	Robinia pseudoacacia	Bark, leaves, seeds and pods	Toxalbumins, including robin	Moderate to high	Dose not well established	Variable	Colic, depression, weakness
Nightshades	Solanum spp.	Foliage and berries; varies by species	Steroidal glycoalkaloids	Moderate to high	Species and plant part matter; dose not reliably established	Variable	Drooling, digestive upset, weakness
Black walnut	Juglans nigra	Especially heartwood in bedding	Laminitis-triggering agent; exact mechanism uncertain	High for bedding exposure	Contact exposure; not a useful eaten-dose comparison	Rapid	Hot feet, reluctance to move
Oak	Quercus spp.	Acorns, buds, young leaves	Tannins	Moderate to high	Heavy or repeated consumption is a concern	Variable	Colic, manure changes, weakness
Buttercup	Ranunculus spp.	Fresh leaves and stems	Protoanemonin	Lower to moderate	Larger fresh amounts are generally more concerning	Relatively rapid irritation	Drooling, mouth irritation, digestive upset

Plants that can kill quickly

Yew, oleander, hemlocks, and wilted cherry can cause a rapidly developing crisis. Don’t assume there will be time to see warning signs. Yew is especially dangerous: reported exposures can cause sudden respiratory or cardiac failure.

Plants that cause cumulative or seasonal illness

Ragwort exposure can build toward liver damage, while bracken fern can interfere with thiamine availability after repeated consumption. Red maple is a seasonal and storm-related concern rather than simply a cumulative one: fallen, wilted leaves can injure red blood cells.

Box elder (Acer negundo) seeds can contain hypoglycin A, associated with seasonal pasture myopathy, a severe muscle disease. Suspected seed exposure, weakness, stiffness, or dark urine requires an immediate call. Don’t confuse US box elder with every tree locally called sycamore; ask extension to identify the actual species.

How to Identify Poisonous Plants in Your Horse Pasture, Region by Region

Walk fence lines, ditches, gates, shaded corners, and bare patches as well as the center of the field. Photograph the whole plant and take close-ups of the leaf, stem, flowers or seeds, and base. A county extension office or state agricultural university can help identify an unknown specimen and provide a local list of plants toxic to horses.

Field ID cards and dangerous lookalikes

• Tansy ragwort: A leafy rosette can develop into an upright plant with clusters of yellow, daisy-like flowers. Several harmless and harmful weeds have similar yellow flowers—many owners wonder whether goldenrod is poisonous—so don’t identify it from color alone.
• Poison hemlock: Look for a tall, branching plant with finely divided leaves, umbrella-shaped clusters of small white flowers, and typically smooth stems with purple blotches. It can resemble wild carrot or Queen Anne’s lace. Don’t rely on a single stem feature to declare a plant safe.
• Water hemlock: Often found in wet ground or drainage areas, it has white flower clusters and divided leaves. It can resemble other members of the carrot family. The root is especially dangerous; leave uncertain plants undisturbed until you have a safe removal plan.
• Nightshades: Appearance differs by species, but look for branching plants with star-shaped flowers or berries. Berry color alone cannot establish safety.
• Bracken fern: Large, triangular-looking fronds may arise from spreading underground rhizomes, often along woodland edges. Other ferns look similar; ask for identification rather than assuming a fern is harmless.
• Buttercup: Glossy yellow flowers and lobed leaves are familiar clues, but species vary. Fresh plants can irritate the mouth; horses may eat them when better forage is scarce.

Don’t use smell, a plant-identification app, or whether wildlife eats a plant as a safety test. Fence off an unknown plant until it’s identified, especially when it resembles a hemlock.

Regional shortlists: Northeast and Great Lakes, Southeast, Midwest and Plains, West, and arid Southwest

These are starting points, not boundaries. Local habitat and landscaping matter more than state lines.

• Northeast and Great Lakes: Check red maple leaf-drop zones, hemlocks in wet or disturbed ground, buttercup in thin pasture, and the source of walnut-containing bedding.
• Southeast and Gulf: Inspect ornamental oleander, cherry limbs after storms, black locust, and unfamiliar landscape shrubs such as cestrum. Ask extension which species are confirmed hazards locally.
• Midwest and Plains: Check nightshades, hemlocks, black locust, and floodplain or ditch vegetation. Look for box elder seeds and seedlings where horses can reach them.
• Mountain West and Pacific: Check for water hemlock near wet areas, tansy ragwort where established, and regionally important larkspur or locoweed. Local identification is particularly important because species differ.
• Arid Southwest: Drought and sparse forage can push horses toward weeds and landscape plants. Inspect oleander hedges, windblown clippings, and irrigated areas where unfamiliar plants may persist.

Toxic trees, shrubs, and ornamentals around the barn

Inspect beyond the fence. Red maple, wild cherry, black locust, oak, yew, and oleander can reach horses as fallen leaves, branches, pods, or prunings. Black walnut is a particular bedding concern; ask exactly what wood is in mixed shavings. Foxglove (Digitalis spp.) is another dangerous ornamental containing cardiac glycosides.

A fence beneath a canopy may not stop windblown leaves or seeds. Tell neighbors and landscaping crews never to dump garden waste or hedge trimmings into a paddock, even if horses appear interested in eating them.

Are Dried Toxic Plants in Hay Still Dangerous? A Buyer’s Guide and Disposal Plan

Yes. Drying doesn’t make many toxic plants safe, and a horse can’t easily sort every fragment out of a bale. Hay, bedding, feed, and clippings can expose a horse even when the pasture looks clean.

Which toxins survive drying and which fade

• Still dangerous: Ragwort retains its liver-damaging alkaloids in hay and may be eaten more readily when dried. Yew and oleander clippings also remain dangerous. Wilted or dried red maple leaves are a particular concern.
• Reduced by drying: Buttercup’s irritating toxin generally diminishes when the plant is thoroughly dried in hay. That doesn’t establish that a questionable bale is safe.
• Uncertain or unidentified: Drying changes how plants look, and toxin persistence varies by species and conditions. Don’t assume an unknown dried weed has lost its toxicity; isolate the hay and ask the vet or extension office.

Questions to ask your hay supplier

Ask where the hay was cut, whether fields border trees or ornamental plantings, and whether ragwort, hemlock, nightshade, or other weeds were present. Ask whether weeds were sprayed before cutting, whether you can inspect bales, and what happens if contamination is found. Keep the supplier and lot information in a feed log.

Before feeding a new load, open several bales from different parts of the stack. Look for unfamiliar stems, flowers, seedheads, broad tree leaves, berries, uneven color, or a musty odor. Mold is a separate feed-safety concern. A clean-looking sample doesn’t guarantee that every bale is clean.

Safe disposal of contaminated bales

Stop feeding the suspect batch and keep it away from horses and wildlife. Photograph the bale and fragments; bag and label a sample with the date, supplier, and stack or field if known. Contact the supplier and ask extension for identification. Call the vet if a horse may have eaten the material.

Arrange return or disposal under local rules. Don’t spread suspect hay on pasture or compost it for pasture use: plant material or seed may remain a risk. Ask local waste authorities or extension about accepted landfill disposal and any burning restrictions.

How to Remove Poisonous Weeds Like Ragwort and Stop Them Coming Back

Removal works best as a repeatable pasture-management plan, not a single mowing. First, fence horses away from a suspect patch. Then identify the plant and choose a method suited to the species and site.

Pulling, bagging, and follow-up for ragwort

Wear gloves and dig or pull ragwort with as much of the root as possible, preferably when the soil is moist. Bag plants, flowers, and seedheads, and remove them from animal access. Don’t leave pulled or wilted plants in the field, where they may remain toxic and become easier to eat. Revisit the site through the season and record regrowth on a pasture map.

For a large infestation, ask extension about a coordinated removal plan and disposal requirements. Protect yourself around hemlocks and other hazardous plants; avoid unnecessary cutting or handling until you know what you’re dealing with.

Pasture management and fencing to reduce re-exposure

Maintain dense forage, rotate paddocks where practical, reseed bare areas, and avoid grazing grass down to the soil. Provide suitable supplemental hay when pasture is short. These steps reduce pressure to eat unfamiliar plants but don’t make a toxic plant safe.

Fence horses away from dangerous trees, hedgerows, and drainage areas, allowing for branches that overhang the fence. After storms, inspect before turnout and remove fallen maple and cherry limbs and leaves. Check fence lines for clippings dropped or blown in from outside.

Why mowing and herbicides need care

Mowing alone may leave toxic material within reach or spread mature seed. Some sprayed or wilting plants can become more attractive while remaining hazardous. Keep horses away from treated areas until the herbicide label permits grazing and hazardous plant material has been dealt with.

Products containing 2,4-D or dicamba aren’t interchangeable prescriptions for every weed or pasture. Ask extension about identification, appropriate control, desirable forage, application restrictions, and label directions. Don’t treat a label’s grazing interval as proof that dead toxic plants are harmless.

Seasonal Pasture-Safety Checklist and Your Next Steps

Spring, summer and drought, autumn leaf fall, and post-storm checks

Season or event	Risk driver	Plants and hazards to check	Action to take
Spring growth	Young weeds appear in thin pasture	Ragwort and hemlock rosettes, buttercup, young bracken, box elder seedlings	Walk before turnout; identify and fence off suspect patches.
Summer grazing	Short forage encourages browsing	Nightshades, ditch plants, locust sprouts, fence-line shrubs	Rotate where practical and provide suitable forage.
Drought	Familiar forage becomes scarce	Normally avoided weeds and stressed ornamentals	Check frequently for chewed plants; supplement forage and reduce grazing pressure.
Late summer seed drop	Seeds spread or become available to horses	Ragwort seedheads, box elder seeds, hemlock seed stalks	Contain seed-bearing material and ask extension about control.
Autumn	Leaves and acorns fall into reach	Wilted red maple and cherry leaves, oak acorns	Fence drop zones and remove accessible debris.
After storms or frost	Branches fall; plants may wilt or change	Cherry and maple limbs, broken shrubs, blown hedge clippings	Inspect and clear the area before turnout. Ask extension about local frost-related plant risks.
Winter and stored-feed periods	Greater reliance on hay and bedding	Dried weeds, tree leaves, black walnut shavings	Inspect new loads and confirm bedding ingredients.
Year-round	Small patches persist or return	Bare ground, rosettes, regrowth, dumped yard waste	Update a pasture map and recheck previously treated sites.

Endophyte-infected tall fescue is another management issue, particularly for pregnant mares. Discuss forage and broodmare management with your veterinarian and extension office. It’s a different risk from identifying a single poisonous broadleaf weed.

Your first-week action list

1. Save your veterinarian’s emergency number and post the barn wall card where everyone can find it.
2. Walk each turnout area, including ditches, tree lines, gates, and neighboring hedges. Photograph and fence off unfamiliar plants.
3. Open and inspect several bales from the current hay supply; record the supplier and lot.
4. Check bedding ingredients and make sure prunings and storm debris cannot enter the paddock.
5. Ask your county extension office for a local plant list and help with uncertain specimens. Mark findings and removal dates on a pasture map.

If you find a suspect plant and no horse has eaten it, prevent access, photograph it, and identify it before safe removal. If a horse may have eaten it, call the vet and follow the emergency protocol. Focus first on the highest-risk plants and exposure routes, not on eliminating every weed.

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FAQ

Is buttercup poisonous to horses?

Yes, but it is mainly an irritant. Fresh buttercup can cause mouth blistering, drooling, and colic or diarrhea if eaten in quantity. Horses usually avoid it unless forage is scarce, and drying in hay greatly reduces its toxicity.

Will horses avoid poisonous plants on their own?

Often, when plenty of good forage is available, but not reliably. Overgrazed pasture, hunger, boredom, and wilted or dried plants in hay or clippings can lead horses to eat plants they would normally skip.

Are red maple and wild cherry leaves dangerous to horses?

Yes, particularly when the leaves are wilted or dry after a storm or in autumn. Red maple leaves can damage red blood cells and cause dark urine, while wilted cherry leaves can release cyanide. Remove fallen branches promptly and call a vet if a horse may have eaten them.

What is the difference between toxic plants and injurious plants like foxtail?

Toxic plants harm a horse through chemicals absorbed after eating them. Injurious plants like foxtail have sharp awns that cause mechanical damage such as mouth sores, and they are usually treated by removing the cause and caring for the injury.

Does mowing make poisonous weeds safe for horses?

No. Mowed or wilted weeds can remain toxic and may be more palatable to horses, and mowing can spread seed. Pull and bag weeds like ragwort and keep horses off the area until the plant material is removed.