Plants Toxic to Horses

Lily-of-the-valley plant

Happy / Pixabay

If you have horses and a garden, you'll have to be careful that you do not have certain plants on your property. These common weeds, trees, plants, and shrubs, shown below, are toxic to horses and ponies. Learn to identify these plants in your pastures and yards and be sure to remove them as soon as possible to keep your horses safe.

  • 01 of 11

    Deadly Nightshade

    deadly nightshade
    Merma1d / Getty Images

    Deadly nightshade can thrive even in dry conditions. It yields a bell-shaped purple flower and the small, round fruit looks like a large black currant, of a deep, shiny black/purple color. All parts of this plant are toxic to humans and pets. The fruit is somewhat sweet, therefore adding to its danger.

    The leaves are dark green and smooth-textured, somewhat similar to that of a tomato plant. It belongs to the same family as the tomato, potato, and pepper plants.

    Typically horses accidentally may ingest a toxic plant because it has been baled into the hay. Signs of nightshade poisoning may include:

    • colic-like symptoms
    • loss of muscle control, unable to rise
    • disorientation, stumbling or other neurological signs
    • dilated pupils
    • death (if consumed in large enough amounts)
  • 02 of 11


    buttercup flowers
    Paul Mansfield Photography / Getty Images

    The flowers are yellow and cup-shaped, and plants have sharply lobed leaves. The grass around buttercup plants may be well grazed. If there is more desirable feed available, horses will generally avoid eating buttercups because of their acrid taste and tendency to blister the mouth. After a hard frost or if dried in hay, buttercups are no longer toxic.

    Buttercups may cause:

    • irritation of the mouth area, such as blisters, drooling
    • colic-like symptoms
    • diarrhea
  • 03 of 11

    Bracken Fern

    bracken fern

    Bracken fern is very common, as it can be found growing along roadsides, in fields, in light bushy areas, and even gardens. In the spring, 'fiddleheads' unfurl into triangular fronds. Bracken fern, dried and baled into hay, is still toxic. If a horse eats a large quantity of this fern, the toxins can cause a vitamin B1 deficiency.

    Symptoms of bracken fern poisoning may include:

    • weight loss
    • weakness
    • gait abnormalities
    • abnormal heart rate and/or rhythm
    • inability to rise
    • death
  • 04 of 11

    Horse Tails

    horsetail plant
    PhotoAlto/Frederic Cirou/Getty Images

    Soils comprised largely of sand and gravel drain quickly, making them perfect for this variety of horsetail. Other varieties grow in more marshy areas. The plant can be toxic whether dried and baled into hay, or consumed as the fresh plant. The toxin in this plant inactivates thiamin (vitamin B1) in the horse's gastrointestinal tract.

    Symptoms of horsetail poisoning include:

    • weakness especially in the hind legs
    • depression
    • constipation
    Continue to 5 of 11 below.
  • 05 of 11

    Lamb's Quarters (or Pigweed)

    lambs quarter plant
    Carrol & Carrol / Getty Images

    In some areas, this plant is called pigweed or goosefoot. The leaves can be broad with varying shapes, and are covered in a whitish coating. The stems are smooth, and can be green or have a reddish tinge. The 'flower' looks rather like a small pale green cauliflower cluster. It is a very common weed in gardens.

    A horse would have to eat a large number of lamb's quarters for the toxin to take effect. Unless there is no other feed available, it is unlikely a horse will eat this plant.

    If a horse consumes a large number of lamb's quarters symptoms may include:

    • weakness
    • respiratory distress
    • coma
    • kidney failure
  • 06 of 11

    Lily of the Valley

    lily of the valley
    Westend61/Getty Images

    It's a lovely spring-blooming perennial bulb, but it's toxic to horses. Does this grow in your flower garden?

    This common garden plant is toxic to humans and pets, including horses. Lily of the valley is unlikely to be growing in a pasture, as it is typically planted in house gardens because of its attractive flowers and pretty red berries. It could be accidentally ingested if someone were to throw garden clippings close to a fence line where curious horses might be able to reach. Garden and lawn clippings should be disposed of in an area that is out of the reach of horses.

    The plant's toxins affect the heart. Ingestion may result in:

    • irregular heart rhythm
    • low blood pressure
    • seizures
    • colic
    • weakness
    • death
  • 07 of 11


    Deb Perry/Getty Images

    Milkweed is a very common pasture plant. Elliptical shaped leaves branch off of a central stem. Within the plant is a white, sticky sap. The flowers grow in a ball-shaped cluster and when in full bloom can range from a pink to purplish color. The pods develop to about 3" and in fall, split open to release brown seeds that float through the air on downy white fluffy fibers. All parts of the plant are toxic. Green, fresh plant material and dried plants (accidentally baled into hay) are toxic. Like most toxic plants, horses will avoid milkweed unless they have no other food source. Signs of milkweed poisoning are:

    • weakness
    • seizures
    • respiratory difficulties
    • coma
    • death

    Milkweed is the host plant for the important pollinator, the monarch butterfly. So, although it should not be present in hay fields, safely planting this flower in beds away from grazing livestock is acceptable.

  • 08 of 11


    amaranthus pigweed
    Bill Barksdale / Getty Images

    Pigweed can be very toxic if eaten in large quantities. Horses are unlikely to eat this plant unless there is no other food available. This weed seems to grow everywhere, from pastures to vegetable gardens, roadsides to barnyards. It is still toxic if dried and baled into hay. Pigweed and its relative, lamb's quarters, can cause kidney failure. Other symptoms of pigweed ingestion may include:

    • weakness, muscle tremors
    • lack of coordination
    • kidney failure
    Continue to 9 of 11 below.
  • 09 of 11

    Red Maple

    red maple leaves
    Xia Yuan / Getty Images

    The bark of red maples is smooth and grayish. The twigs are reddish-brown.

    The wilted and fallen leaves can be toxic to horses. The toxins destroy the red blood cells. Just 1.5 to 3 pounds of ingested red maple leaves can be lethal.

    Leaves can remain toxic for several weeks after they've fallen. Don't dispose of red maple leaves in manure piles or compost heaps that might be within the reach of your horses. Red maple leaves can cause problems if baled into hay.

    Red maples grow throughout the eastern United States and Canada.

    Symptoms of red maple poisoning are:

    • breathing difficulties
    • jaundice
    • dark brown urine
    • death
  • 10 of 11

    Red Oak

    oak tree
    John Lawson / Getty Images

    Various varieties of oaks grow throughout North America. Horses will eat the leaves if there is no other food available. Water may be contaminated by fallen leaves. Acorns are also toxic if eaten in sufficient quantities.

    Signs of oak poisoning are:

    • poor appetite
    • weight loss
    • diarrhea
    • increased drinking
    • increased urination
    • kidney failure
    • edema
    • death
  • 11 of 11

    St. John's Wort

    st. johns wort
    Westend61/Getty Images

    St. John's Wort blooms from May to August and can tolerate most soil types, but prefers moist soil with good drainage. If you crush the flowers between your fingers, it will leave a rusty reddish stain. St. John's Wort causes photosensitivity when ingested by livestock. Animals may have blistered skin and white areas of the coat may be more prone to sunburn.

If you suspect your pet is sick, call your vet immediately. For health-related questions, always consult your veterinarian, as they have examined your pet, know the pet's health history, and can make the best recommendations for your pet.
Article Sources
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  1. Plants Toxic to Horses. Penn State Extension

  2. Field horsetail and brackenfern: harmful plants to horses. University of Minnesota Extension, 2020

  3. Toxic Plants of Kansas. Kansas State University Veterinary Health Center

  4. Spring Plants that are Poisonous to Horses, Dogs and Barn Cats. Penn State Extension