(Robinia pseudoacacia)

Black Locust Tree

Black locust, which is poisonous to horses.

Plant Description

The black locust tree is a tree that is usually grows to a height of 30-50 feet, though it can grow as tall as 50-70 feet. It has white blooms for only 10 days during the spring, and black seedpods will be present on the tree throughout winter.

Geographic Locations

The black locust is found throughout the United States and most of Canada, as it is a native species. It is extremely aggressive and hardy, making it found in almost every environmental and soil condition.

Toxic Plant Components

The bark, seeds, and leaves of the black locust are all poisonous. It is poisonous whether fresh or dried, so it is especially important to avoid tying horses to these trees or hitching posts made from their wood.

Toxicity Cause and Symptoms

The tree is toxic because it produces robin, an extremely potent phytotoxin (simply a toxin produced by a plant). If a 1000 pound horse eats just a half-pound of the leaves or bark, it can be fatal! Horses can become ill within hours of consuming black locust.

Symptoms of poisoning by black locust include:

  • Colic
  • Weakness
  • Renal (kidney) failure
  • Fast heartbeat (tachycardia)
  • Depression
  • Loss of appetite

Cure and Treatment

Poisoning is curable, though it is of limited value. Supportive therapy as well as detoxification is the usual treatment.


More Black Locust Pictures

On the left is a picture of the thorns, and on the right is a picture of the leaves.

Thorns of black locust, which is poisonous to horses.Thorns of black locust, which is poisonous to horses.
Leaves of black locust, which is poisonous to horses.Leaves of black locust, which is poisonous to horses.

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