English
Autumn crocus (Colchicum autumnale), also known as meadow saffron, is a highly toxic plant that can pose a serious risk to horses in pastures, hay fields, and forage. This herbaceous perennial is native to Europe, but it is also cultivated ornamentally in other regions, including North America.
All parts of autumn crocus contain toxic alkaloids, and the corms and seeds are considered especially dangerous. In horses, ingestion can cause severe and potentially fatal poisoning by disrupting normal cell function throughout the body, leading to gastrointestinal, neurologic, respiratory, and systemic effects.
Clinical signs can develop rapidly after ingestion, and severe cases may progress quickly. Keep reading to learn how to identify autumn crocus, why it is toxic to horses, what signs to watch for, and how to reduce the risk of exposure.
Autumn Crocus Poisoning in Horses
Autumn crocus (Colchicum autumnale) is a perennial, corm-forming plant in the Colchicaceae family.
Although commonly called a crocus because it superficially resembles true crocus flowers, it is unrelated to members of the iris family. Instead, it belongs to a distinct botanical group characterized by the production of colchicine and related alkaloids.
The species is native to Great Britain, Ireland, and large areas of mainland Europe, where it occurs naturally from Portugal eastward to Ukraine. In North America, autumn crocus is cultivated primarily as an ornamental plant and has been reported in several regions, including Oregon, Utah, Vermont, New York, Massachusetts, New Hampshire, Virginia, and Kentucky. [1][2][3]
Autumn crocus typically grows in lowland grassy meadows, open fields, roadsides, and disturbed grassy habitats. It may also occur in hay-producing areas, creating the potential for dried plant material to become incorporated into forage. Although escaped ornamental populations are relatively uncommon, the plant may occasionally grow in open sites surrounding gardens and landscaped properties. [1][2][3]
In horses, autumn crocus is one of the more dangerous plants associated with pasture exposure and contaminated hay. Poisoning may occur after direct grazing or ingestion of harvested forage, and because toxicity persists after drying, hay contamination remains a particularly important risk factor.
Other common names for autumn crocus include:
- Meadow saffron
- Naked ladies
- Fall crocus
- Colchicum
- Naked boys
- Sons before the father
Table 1. Autumn crocus poisoning in horses at-a-glance
| Category | Key Information |
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| Definition |
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| Primary Cause |
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| Common Causes |
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| Onset |
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| Symptoms |
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| Severity |
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| Treatment |
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| Recovery Time |
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| Prognosis |
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| Prevention |
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Identification
Autumn crocus is a small herbaceous perennial that grows from an underground, bulb-like corm. One of the plant’s most distinctive features is its unusual seasonal growth cycle: flowers and leaves emerge at different times of year rather than appearing together.
Flowers
Leaves
The plant typically blooms in early autumn, producing showy, cup-shaped flowers that range from pale pink and lavender to deeper purple or white. Flowers emerge directly from the ground without accompanying leaves and may appear singly or in clusters of up to six blooms from the underground corm. Individual flowers are upright and elongated, with narrow floral tubes extending below the soil surface. Â [1]
In contrast to the autumn flowering period, leaves emerge during the spring together with developing fruit capsules. The foliage is generally broad, smooth, fleshy, and lance-shaped, with leaves arising in clusters from the base of the plant. [1]
Leaves may continue through early or mid-summer, often persisting until July before gradually dying back. This marked seasonal separation between flowering and leaf production is one of the most useful identifying characteristics of the species. [1]
The underground corm is rounded and enclosed in dark brown papery sheathing. Because the plant remains dormant underground for much of the year, above ground growth may appear suddenly on a seasonal basis. Both the corm and seeds contain particularly high concentrations of toxic alkaloids. [1]
Autumn crocus most commonly occurs in: [1]
- Grassy meadows
- Pasture margins
- Open fields
- Hay-producing areas with moist, well-drained soils
The plant may also occur in unmanaged grassy sites, roadside habitats, and occasionally around ornamental plantings. Horses may eat the plant while grazing in pasture, but they can also be exposed through contaminated hay, since the plant remains toxic after drying. This type of exposure can be harder to detect because the dried plant may be mixed in with the hay. [1]
Table 2. Autumn crocus identification guide for horse owners
| Plant feature | What to look for | When it appears |
|---|---|---|
| Flowers |
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| Leaves |
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| Fruit capsules |
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| Corms |
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Toxicology of Autumn Crocus
All parts of Colchicum autumnale are toxic to horses, although toxin concentrations are highest in the corms and seeds. The primary toxic compound is colchicine, a potent cytotoxic alkaloid that can damage cells and cause serious effects throughout the body. [1][4][5]
Several closely related alkaloids are also present, including: [1][4][5]
- Colchicoside
- Demethyl desacetylcolchicine
- Colchiceine
- Isocolchicine
The toxic effects of autumn crocus result primarily from disruption of normal microtubule formation within cells.
Microtubules are structural cell components that: [1][4][5]
- Help maintain cell shape
- Support intracellular transport
- Enable cell division
Colchicine disrupts this process by blocking the proteins needed to build microtubules. Without working microtubules, cells cannot properly separate their chromosomes during cell division. This prevents affected cells from dividing and functioning normally. [1][4][5]
Tissues made up of cells that divide quickly or use a lot of energy are especially vulnerable to damage. In horses, significant damage may occur within the following systems: [1][4][5]
- Gastrointestinal tract
- Bone marrow
- Nervous system
Colchicine also disrupts the transport systems that move materials within cells. This can interfere with how immune cells move and break down damaged or harmful material. In nerves, it can disrupt the movement of substances along nerve fibers, which may contribute to weakness, poor coordination, and nerve damage. [1][4][5]
After a horse ingests colchicine, the toxin is absorbed quickly and can reach high levels in the blood within about one to two hours. Because it dissolves easily in fat, it can spread widely through the body and build up in tissues such as the bone marrow and liver. Colchicine may also be recycled between the liver and intestines, which can make its toxic effects last longer. [1][4][5]
Unlike some toxic plants that primarily cause localized gastrointestinal irritation, autumn crocus causes severe multisystem cellular injury. Clinical disease can progress rapidly after ingestion, with widespread organ dysfunction contributing to the severity of poisoning.
Importantly, toxicity persists in both fresh and dried plant material. Horses may risk exposure not only while grazing, but also through contaminated hay or harvested forage containing dried autumn crocus plants.
What's your top priority with your horse's health?
What's your top priority with your horse's health?
Symptoms of Autumn Crocus Poisoning in Horses
Clinical signs of autumn crocus poisoning typically develop rapidly after ingestion, often within approximately 2 to 12 hours. Severity depends on the amount consumed, the part of the plant ingested, and how quickly treatment begins. [1][4]
Because colchicine affects multiple organ systems at once, affected horses may develop severe systemic illness involving gastrointestinal, neurologic, cardiovascular, and respiratory abnormalities. [4][6][7]
Clinical signs may include: [4][6][7]
- Difficulty swallowing (dysphagia)
- Colic
- Diarrhea
- Weakness
- Lethargy
- Respiratory distress
- Muscle weakness
- Reduced gastrointestinal motility
- Sweating
- Dehydration
- Recumbency
Gastrointestinal signs are often among the earliest abnormalities observed and may become severe due to extensive injury to rapidly dividing intestinal cells. Horses may initially develop abdominal discomfort, reduced appetite, difficulty swallowing, and diarrhea before progressing to more advanced systemic disease. [4][6][7]
When to Call the Veterinarian
Autumn crocus exposure should be treated as a veterinary emergency. Contact a veterinarian immediately if a horse may have eaten autumn crocus, if suspect plant material is found in hay, or if multiple horses with access to the same forage develop sudden illness.
Call your veterinarian promptly if you observe:
- Colic, diarrhea, reduced appetite, or difficulty swallowing
- Weakness, depression, sweating, or recumbency
- Signs of dehydration, shock, or respiratory distress
- Rapidly worsening signs after pasture or hay exposure
- Autumn crocus plants in a grazing area, hay field, or bale of forage
Veterinary evaluation helps determine whether signs are consistent with poisoning and whether emergency decontamination or intensive supportive care is needed. Do not wait for signs to progress before seeking guidance, because colchicine can be absorbed rapidly and severe cases may decline within hours.
Exposure Risk Factors
Autumn crocus is grown as an ornamental plant in gardens and landscapes, and some species may also be found in meadow or grassland settings. Although commonly called autumn crocus, plants in the genus Colchicum are not true crocuses. Their foliage appears in spring and dies back in early summer, while the flowers emerge in autumn, which can make the plant harder to recognize at different times of year. [2][3]
Horses may be exposed when autumn crocus grows in or near grazing areas, or when ornamental plant material, garden waste, or contaminated forage becomes accessible. Because different plant parts appear at different times of year, owners may notice spring leaves, autumn flowers, or underground corms depending on the season. [2][3]
Exposure can also occur through contaminated hay or roughage. Meadow saffron has been associated with hay-related poisoning and colic in horses, and dried plant material can remain hazardous after harvest. One report described a hay delivery heavily contaminated with Colchicum autumnale, after which several horses developed colic and one horse died. [6]
All parts of the plant are toxic, including the leaves, flowers, seeds, and corms. Toxicity is caused primarily by colchicine and related alkaloids, which interfere with normal cell division and can cause severe gastrointestinal and systemic effects. [1][3][7][9]
Horses should not be allowed to graze areas where autumn crocus is present or consume hay suspected to contain the plant. Any known or suspected ingestion should be treated as a potential poisoning risk, and owners should contact a veterinarian immediately.
Diagnosis
Diagnosis of autumn crocus poisoning is based primarily on a history of exposure, compatible clinical signs, and identification of the plant in the horse’s environment or feed. Because there are no specific diagnostic tests for colchicine toxicity in horses, diagnosis depends largely on clinical evaluation and environmental evidence.
A detailed history should include whether the horse had possible access to: [8]
- Autumn crocus growing in pasture or meadows
- Contaminated hay or harvested forage
- Ornamental plantings
- Recently mowed or disturbed grassy areas
- Escaped ornamental populations near grazing sites
Clinical findings may include signs of severe gastrointestinal irritation, weakness, respiratory compromise, dehydration, and shock developing within hours of ingestion. Bloodwork results are often not specific to this poisoning but may show signs of dehydration and damage affecting multiple body systems. [8]
Depending on severity and progression, abnormalities in bloodwork results may include: [8]
- Hemoconcentration associated with fluid loss
- Electrolyte disturbances
- Indicators of organ dysfunction
- Acid-base abnormalities
- Evidence of systemic inflammation or shock
Pasture inspection and careful examination of hay or forage may help identify the source of exposure, particularly because dried autumn crocus remains toxic after harvesting.
Treatment & Management
Treatment of autumn crocus poisoning focuses on reducing further toxin absorption while providing aggressive supportive care to manage systemic effects. Because colchicine is rapidly absorbed and widely distributed throughout the body, early intervention is critical, and prognosis worsens substantially once severe clinical signs develop.
All access to contaminated pasture, hay, or suspect plant material should be eliminated immediately. Horses should be removed from affected grazing areas and provided with clean forage and water while the source of exposure is identified.
Activated charcoal may be administered to reduce absorption of alkaloids remaining within the gastrointestinal tract. In some cases, gastric lavage may also be considered, particularly when ingestion is recognized very early. [9]
Supportive treatment focuses on: [9]
- Keeping the horse hydrated
- Supporting normal circulation and heart function
- Reducing the risk of complications
Fluid therapy including dextrose and calcium may be administered, and cathartics may be used to assist elimination of residual toxin from the gastrointestinal tract. [9]
Additional supportive measures depend on the severity of clinical signs and may include intensive monitoring, management of shock, correction of electrolyte abnormalities, and supportive nursing care. Because poisoning can progress rapidly, affected horses often require close veterinary supervision during the acute phase of illness.
Gastrointestinal decontamination should only be performed by a veterinarian. Do not attempt nasogastric intubation or administer activated charcoal, mineral oil, or other laxatives without a veterinarian.
Prognosis
The prognosis for horses affected by autumn crocus poisoning by varies depending on the amount ingested and the speed of intervention.
Severe poisoning may carry a poor prognosis due to the widespread cellular injury produced by colchicine and related alkaloids. [7][9]
Prevention
Prevention of autumn crocus poisoning relies primarily on careful pasture monitoring, forage inspection, and limiting horse access to areas where the plant may grow. Because the plant remains toxic in both fresh and dried forms, prevention strategies must address both direct grazing exposure and contamination of harvested forage.
Horse owners and pasture managers should routinely inspect grazing areas, hay fields, and meadow environments for autumn crocus, particularly during the flowering period in early autumn and during spring leaf emergence. Recognizing the plant’s unusual seasonal growth pattern may support early identification before significant exposure occurs.
Hay should be inspected carefully for dried plant material, especially when forage originates from lowland meadows or unmanaged grassy areas where autumn crocus may occur naturally. Contaminated hay represents a particularly important risk because horses may consume dried plant material when it is mixed within baled forage.
Pasture management practices that maintain dense, healthy forage growth may help reduce opportunities for toxic plants to establish within grazing areas. Preventing overgrazing is also important, as horses are more likely to consume undesirable plants when forage availability becomes limited.
Because autumn crocus is also cultivated ornamentally, horses should be prevented from accessing gardens, landscaped areas, or compost containing discarded plant material. Escaped ornamental populations may occasionally establish in nearby grassy sites and should be removed promptly when identified.
Frequently Asked Questions
Here are some frequently asked questions about autumn crocus poisoning in horses:
Autumn crocus is highly poisonous to horses and should not be accessible in pastures, hay fields, or areas near turnout. All parts of the plant contain colchicine and related toxic alkaloids that can disrupt normal cell function throughout the body. Poisoning can affect the gastrointestinal tract, nervous system, respiratory system, cardiovascular system, bone marrow, and other active tissues. Exposure should be treated as a serious veterinary concern because severe cases can be fatal.
Meadow saffron is poisonous to horses because it is another common name for autumn crocus. The plant contains colchicine, a potent alkaloid that interferes with cell division, intracellular transport, and normal tissue function. Horses may be exposed by grazing the plant directly or by eating contaminated hay. Any suspected access to meadow saffron should be treated as a veterinary emergency.
The corms and seeds are considered the most toxic parts of autumn crocus for horses because they contain especially high concentrations of toxic alkaloids. However, the leaves and flowers are also dangerous and should not be considered safe. The whole plant remains a poisoning risk whether it is eaten fresh in pasture or dried in hay. Preventing access to all plant parts is the safest approach.
Autumn crocus flowers are poisonous to horses and should not be grazed or handled as safe pasture plants. The flowers usually appear in early autumn and may be pale pink, lavender, purple, or white. They often emerge directly from the ground without leaves, which can make the plant look unusual and easy to miss if owners are only checking for spring foliage. Horses should be kept away from flowering autumn crocus plants and any areas where flowers have been found.
Autumn crocus leaves are poisonous to horses, even though the corms and seeds contain the highest toxin concentrations. The leaves appear in spring with developing fruit capsules and are broad, smooth, fleshy, and lance-shaped. Because the leaves are not present during the autumn flowering period, owners may need to inspect pastures at more than one time of year to identify the plant. Horses should not be allowed to graze areas where autumn crocus foliage is growing.
Dried autumn crocus remains toxic in hay and can still poison horses after harvest. This makes contaminated forage a major concern because dried plant fragments may be difficult to recognize once mixed into baled hay. Horses may eat the plant accidentally when it is hidden among otherwise normal forage. Hay from lowland meadows, unmanaged grassy areas, or fields where autumn crocus may grow should be inspected carefully before feeding.
If a horse eats autumn crocus, colchicine can be absorbed quickly and spread widely through the body. The toxin damages cells that divide rapidly or use a lot of energy, which helps explain the severe effects on the gastrointestinal tract, bone marrow, nervous system, and other tissues. Early signs may include colic, diarrhea, reduced appetite, difficulty swallowing, weakness, depression, sweating, and reduced gut motility. Severe poisoning can progress to dehydration, shock, respiratory distress, recumbency, and death.
Signs of autumn crocus poisoning in horses often appear within approximately 2 to 12 hours after ingestion. Colchicine can reach high blood levels within about one to two hours and then distribute into tissues throughout the body. Because multiple organ systems may be affected at the same time, a horse's condition can worsen rapidly once signs begin. Veterinary guidance is needed as soon as exposure is known or suspected.
Signs of autumn crocus poisoning in horses can include colic, diarrhea, difficulty swallowing, reduced appetite, weakness, depression, sweating, dehydration, reduced gastrointestinal motility, muscle weakness, respiratory distress, shock, and recumbency. Digestive signs are often among the first problems noticed because intestinal cells are especially vulnerable to colchicine toxicity. Neurologic, respiratory, cardiovascular, and systemic signs may develop as poisoning progresses. Sudden illness after possible pasture or hay exposure should be treated as urgent.
Autumn crocus poisoning can cause colic in horses because colchicine can severely injure the gastrointestinal tract. Affected horses may also develop diarrhea, reduced appetite, difficulty swallowing, dehydration, and reduced gut motility. These signs are not specific to autumn crocus poisoning, so exposure history and plant identification are important. Call a veterinarian promptly if colic occurs after a horse may have accessed autumn crocus or contaminated hay.
Autumn crocus poisoning can cause neurologic signs in horses because colchicine can interfere with transport systems inside nerve cells. Affected horses may show weakness, muscle weakness, depression, poor coordination, or nerve-related dysfunction as poisoning progresses. These signs may occur alongside gastrointestinal, respiratory, and cardiovascular abnormalities. Neurologic signs after possible autumn crocus exposure require immediate veterinary attention.
Autumn crocus poisoning can cause breathing and circulation problems in horses, especially in severe cases. Reported signs include respiratory distress, shock, weakness, dehydration, and systemic illness involving multiple body systems. These problems may develop as cellular injury, fluid loss, and organ dysfunction progress. Horses showing respiratory distress, collapse, severe weakness, or signs of shock need emergency veterinary care.
A safe amount of autumn crocus for horses cannot be reliably predicted. Risk depends on the amount eaten, the plant part consumed, the horse's condition, and how quickly exposure is recognized. The corms and seeds are especially dangerous, but all parts of the plant are toxic. Because severe poisoning can develop quickly, horses should not be allowed to eat any autumn crocus.
If your horse ate autumn crocus, remove the horse from the contaminated pasture, hay, or plant material immediately and call a veterinarian. Prevent further access to suspect forage while keeping the horse in a safe area with clean hay and water. Do not wait for severe signs to appear, because colchicine is absorbed quickly and early intervention is important. If possible, preserve a sample of the plant or hay for identification.
Autumn crocus poisoning in horses is diagnosed mainly through exposure history, compatible clinical signs, and identification of the plant in the horse's environment or feed. There are no routinely available specific diagnostic tests for colchicine toxicity in horses. A veterinarian may assess hydration, gastrointestinal function, respiratory status, circulation, organ function, electrolyte balance, acid-base status, and signs of shock. Inspection of pastures, hay fields, ornamental plantings, and hay can help confirm the likely source.
Autumn crocus poisoning in horses is treated with emergency veterinary care focused on reducing further toxin absorption and supporting affected body systems. Treatment may include removing access to the plant, activated charcoal, gastric lavage in very early cases, cathartics, fluid therapy, dextrose, calcium, electrolyte correction, and shock management. Care depends on the severity of signs and may require close monitoring during the acute phase. There is no simple home treatment that can replace veterinary care for suspected colchicine poisoning.
A horse can recover from autumn crocus poisoning, but the prognosis depends on the amount eaten and how quickly treatment begins. Severe cases have a guarded to poor prognosis because colchicine can cause widespread cellular injury and multisystem illness. Horses with rapid recognition, early decontamination, and intensive supportive care have a better chance than horses treated after advanced signs develop. Ongoing veterinary monitoring is important because clinical signs can worsen quickly.
Horses are most likely to encounter autumn crocus in grassy meadows, pasture margins, open fields, roadsides, disturbed grassy habitats, hay-producing areas, and sites near ornamental plantings. The plant prefers moist but well-drained soils and may occur in lowland meadow environments. In North America, it is more often grown as an ornamental, but escaped plants may occasionally establish in nearby grassy areas. Hay contamination is a particular concern when forage is harvested from areas where autumn crocus grows.
Horse owners can identify autumn crocus by its unusual growth cycle, with flowers and leaves appearing at different times of year. The plant produces cup-shaped pink, lavender, purple, or white flowers in early autumn, often without any leaves present. Broad, smooth, fleshy leaves appear in spring with developing fruit capsules and may die back by summer. This separation between autumn flowers and spring foliage is one of the most useful identification clues.
Autumn crocus is not the same as true crocus, even though the flowers may look similar. Autumn crocus belongs to the Colchicaceae family, while true crocuses belong to the iris family. The distinction matters because autumn crocus contains colchicine and related alkaloids that are highly toxic to horses. If a crocus-like plant appears in or near horse areas, identify it carefully before assuming it is harmless.
You can help prevent autumn crocus poisoning in horses by inspecting pastures, meadow areas, hay fields, and hay for the plant. Check during early autumn flowering and again during spring leaf emergence, since the plant looks different at each stage. Prevent overgrazing so horses are less likely to eat undesirable plants when forage is limited. Horses should also be kept away from gardens, landscaped areas, compost piles, and discarded ornamental plant material that may contain autumn crocus.
Summary
Autumn crocus, also known as Meadow Saffron, is a highly toxic plant that can endanger horses when present in pastures, hay fields, and contaminated forage.
- All parts of the plant are toxic, with the corms and seeds considered especially dangerous
- The main toxin, colchicine, disrupts normal cell function and can cause severe multisystem illness
- Signs may include colic, diarrhea, difficulty swallowing, weakness, depression, dehydration, shock, respiratory distress, and recumbency
- The plant remains toxic when dried, making contaminated hay a serious exposure risk
- Prevention relies on pasture checks, careful hay inspection, removal of autumn crocus, and urgent veterinary care after suspected ingestion
References
- Burrows. G. E. Toxic Plants of North America. John Wiley & Sons. 2013.
- Mahr. S. Autumn Crocus, Colchicum Spp.. University of Wisconsin Wisconsin Horticulture. 2026.
- Colchicum (Autumn Crocus, Meadow Saffron, Naked Ladies). North Carolina Extension Gardener Plant Toolbox
- Meadow Saffron Poisoning in Horses. HorseDVM.
- Meadow Saffron Poisoning in Cattle. CowDVM. 2026.
- Kamphues. J. and Meyer. H. [Meadow saffron (Colchicum autumnale) in hay and colic in horses]. Tierarztliche Praxis. 1990.
- Gupta. R. C. Veterinary Toxicology: Basic and Clinical Principles. Elsevier. 2012.
- Möller. S. Diagnosis of Colchicum Autumnale Poisoning Using Colchicine Detection in Urine. Equine Veterinary Journal. 2022.
- Plumlee. K. H. Clinical Veterinary Toxicology. Mosby. 2004.
