Poisonous Plants

Possibly the biggest danger of poisonous plants is that many horse owners do not recognize many of them as posing any threat to their equine friend.

In fact, some of of the most common plants used in landscaping around homes and growing naturally around horse pastures and barns can be deadly to horses!

Which parts of a plant are poisonous?

Many different parts of a plant can be poisonous, and some poisonous plants have multiple parts that can cause problems.

The most common parts of the plant that are poisonous are:

  • Leaves
  • Roots
  • Seed/nut
  • Flowers/Blooms
  • Stems

The fruits off of some trees can also be poisonous, or can cause problems if horses have access to them and gorge themselves on ripe fruit.

When is a plant poisonous?

Some plants are poisonous to horses only when they are fresh, while some are poisonous only after they have died or are dried out. Then there are those plants that are poisonous both fresh and dried.

How much is toxic?

It depends on the species of plant to determine how much is toxic. For some plants such as oleander, as little as a few mouthfuls of the right part of the plant can kill a horse in minutes. The yew is another extremely toxic plant, with as little as 8 ounces capable of killing an adult horse in 5 minutes!

Then there are the plants like bracken fern that slowly cause problems and a negative reaction might not occur until months after the plant has been eaten.

It also depends on the growing conditions of the plant...in some growth conditions a plant may be barely toxic, but put it in another growing condition and it could be extremely toxic.

To compound the problem, some plants don't even have to be eaten to be toxic! Black walnut is one example...using shavings from this tree in your stalls will cause laminitis in your horses when a mere 10% of the shavings are black walnut!

What do I do if my horse eats a poisonous plant?

If you suspect your horse has eaten a plant that is poisonous, the first course of action is to call your veterinarian. They will be able to tell you what to do for your horse until they get there.

If the poisonous plant is located in or near a pasture that other horses have access to, remove the horses from the pasture until the plant can be removed.

Which plants are the offenders?

Here is a list of the most common plants that are poisonous to horses. It is by no means absolutely complete, though I have tried to include as many as possible.

Click on the name of the plant to be taken to its page where you will find:

  • Plant information
  • Level of toxicity
  • Picture (if available)
  • Toxicity Symptoms

as well as any other pertinent information about the plant.

So, on to the offending plants:

Alsike Clover


Black Cherry Tree

Black Locust Tree

Black Walnut Tree

Bracken Fern


Castor Bean


Crotalaria species


Firecherry Tree
Ground Ivy

Horse Chestnut






Mountain Laurel



Peach Tree

Plum Tree
Poison Hemlock


Red Maple Tree


Senecio species

Sorghum Grass


Water Hemlock

White Snakeroot

Wild Cherry Tree

Yellow Starthistle


How do I prevent poisoning?

The best way to prevent your horse from consuming one of these plants and becoming ill is to use common sense.

Check your pastures, especially the borders along the fence (BOTH sides of the fence!) and make sure you can identify all the plants growing there. Also make sure none of them are poisonous. If they are, learn how to successfully remove them, and do so.

When grass for grazing is depleted, make sure you supplement your horses with adequate hay. In most instances, horses will not bother poisonous plants, even if they have access to them. However, when they get hungry and no (or poor) grass is available, that is when they will start sampling other plants and get themselves in trouble. Be extra vigilant if you have young or curious horses around, as these groups are more likely to sample unknown plants.

When you are in unfamiliar areas, do not allow your horse to graze unless necessary. If you do allow him to graze, ensure that you know what all the plants within his reach are.

KNOW WHERE YOUR HAY COMES FROM! This is a big one, as many of these plants are toxic when they are dried, and the favored habitat of many of them is on the edge of fields. It is very easy for these plants to get baled into hay, so make sure you are buying from a reputable hay seller, and that he or she knows you are feeding the hay to horses (many of these plants do not affect cattle the same way due to digestive system differences).

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