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.
Deadly nightshade likes sandy soil and thrives even in dry conditions. It has a bell-shaped purple flower and the small, round fruit looks like a large black currant: a deep and shiny black/purple. 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 is in the same family as the tomato, potato, and pepper plants.
Typically horses accidentally ingest a toxic plant because it has been baled into the hay and eaten unknowingly. Signs of nightshade poisoning may include:
- colic-like symptoms
- loss of muscle control, unable to rise
- disorientation, stumbling or other neurological signs
- dilated pupils
The flowers are yellow and cup-shaped with sharply lobed leaves off of a thin stem. The grass around them will be well grazed. Horses will avoid eating buttercups because of their acrid taste and direct blistering of the mouth if there is more desirable feed available. After a hard frost or dried in hay, buttercups are no longer toxic.
Buttercups may cause:
- irritation of the mouth area, such as blisters, drooling
- colic-like symptoms
Bracken fern is very common, growing along roadsides, in fields, in light bush areas, and even gardens. In the spring 'fiddleheads' unfurl into triangular fronds up to 3ft (1m) high. 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:
- loss of coordination
- depressed heart rate
- weight loss
- eventual death if not promptly treated
The soil around my old property is largely sand and gravel. It drains quickly, making it perfect for this variety of horsetail. Other varieties grow in more marshy areas. If the plant is dried and baled into hay the toxin may have a greater effect than in the fresh plant. The toxin in this plant destroys vitamin B in the horse’s blood.
Symptoms of Horsetail poisoning are:
- weakness especially in the hind legs
- apparent blindness due to damage to the central nervous system
- liver disease
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Lamb's Quarters (or Pigweed)
In some areas, this plant is called pigweed or goosefoot. It has smooth, light-colored leaves and a woody red stem. 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:
- respiratory distress
- kidney failure
Lily of the Valley
It's a lovely spring-blooming perennial bulb, but it's deadly 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 out of reach of horses.
The plant's toxins affect the heart. Ingestion may result in:
- irregular heart rhythm
- diarrhea/signs of colic
- sudden death
Milkweed is a very common pasture plant. Elliptical shaped leaves branch off of a central stem. Inside the plant is a white, sticky sap. The flowers grow in a ball-shaped cluster and when in full bloom are a lavender 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. Living 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:
- loss of muscular control
- rapid and weak pulse
- respiratory difficulties
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.
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
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The bark of red maples is smooth and grayish. The twigs are reddish-brown.
The fresh leaves are considered relatively safe, but wilted and fallen leaves can be toxic—but tasty, to horses. The toxins affect the red blood cells. Three pounds of ingested red maple leaves are considered 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 in 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:
- dark brown urine
- rapid pulse
- increased respiration
- blue or yellow gums
Various varieties of oaks live 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 quantity.
Signs of oak poisoning are:
- colic symptoms
- darkened urine
St. John's Wort
From mid-July to mid-August St. John's Wort blooms in dry sandy soil. 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 will have blistering skin and white areas of the coat will easily 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.
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Plants Toxic to Horses. Penn State Extension
Field horsetail and brackenfern: harmful plants to horses. University of Minnesota Extension, 2021
Toxic Plants of Kansas. Kansas State University Veterinary Health Center
Spring Plants that are Poisonous to Horses, Dogs and Barn Cats. Penn State Extension