What Plants are Toxic to Horses?

Toxic plant Chart

After Zelda and Curly’s experience with the acorns, I’ve been thinking about the other plants that are toxic to horses.

Let’s face it. Some horses — like Zelda — will eat just about anything they can get their mouths on. This propensity for sampling new foods can lead to horses eating plants that are toxic. While some of these plants are merely unpleasant, others can be downright dangerous. It’s important for horse owners to be aware of which plants pose a threat to their horses and take steps to prevent them from grazing on these vegetation.

In New England, here are three plants to keep your horse away from — I’m surprised they don’t mention Oak trees a both the leaves and the acorns are toxic — but just add them to the list. Or you can get this handy poster which teaches you what plants are toxic to horses so you can keep them safe. Buy it on Etsy.


In my neck of the woods there are more Rhododendrons than pine trees (practically) which means they are everywhere. Although they are now ubiquitous, Rhododendrons are not native plant. They were introduced to North America in the 1700s from Europe and Asia. Rhododendron berries (blue-black) contain toxins that can cause acute colitis in horses. Luckily none of these are tasty to horses so they typically are only eaten when no other forage is available. There is no “toxic dose” but it’s suggested that a horse would need to eat 1-2 pounds of green leaves to be affected.


Yew is an evergreen tree with dark green needles and bright red berries. Yew is highly toxic to all species, including humans. Be aware that not only is Yew a popular landscaping plant, but also some Christmas wreaths incorporate Yew, so make sure there aren’t any hung at your barn where horses might nibble on them. Eating as little as six ounces of Yew can cause sudden death in a horse.


Buttercups look lovely in a pasture (we have plenty of them where Zelda and Curly live), but the leaves and stems contain protoanemonin, a toxic oil that causes blisters in the horse’s mouth, drooling, diarrhea, and mild colic. The toxin become inactivated when dried so buttercup is not a concern in hay. Buttercups are a bear to get rid of once they take root in a pasture. I have one friend who digs them out by the roots, but that’s a pretty daunting task.

Mowing fields or clipping plants close to the ground in the early spring before buttercup plants can produce flowers may help reduce the amount of new seed produced, but mowing alone will not totally eliminate seed production.

3 thoughts on “What Plants are Toxic to Horses?

  1. Before I understood what they were and how invasive they are, I let an entire pasture be overtaken with Buttercups. I wish I had stepped in sooner. I just didn’t know. We finally got it under control, but it took several years. I still do a combination of weed pulling and spraying each Spring (and sometimes Fall) to keep them at bay. They are very hardy.

  2. Definitely did not know that Rhododendrons are toxic. They’re such a popular ornamental plant. I’ve been told black maple is also toxic to horses; we had an ornamental one at one of my old barns.

  3. Scarlet maple is toxic to horses, I’m not sure about black maple. So are: ox eye daisy, pigweed (amaranth family), common groundsel and it’s look alike cousin Tansy ragwort (it’s a horrible plant. Horses usually won’t touch it unless they’re starving when it’s green. But it gets baled into hay and when it’s dried, it stops being stinky. Livestock eats it and it doesn’t kill them immediatly, no, it accumulates in the liver and kills the poor animal slowly and in great pain. There’s no antidote.)
    As noted in another post, Buttercup is toxic, all the borages, milk and yellow starthistle, Bracken fern, Equisetum (ironically, also called horse tail), most of the lupines and legumes, mustards, Spurges, St. John’s Wort (although I haven’t seen much in the literature about it’s toxicity), and water and poison hemlock. The last is so toxic to all mammals that even touching it can cause blistering.
    In all cases, do NOT compost these plants. Put them in the garbage. Don’t burn them, as standing the the smoke can cause medical problems. For instance, poison ivy is even more toxic to one if one inhales the smoke than if you ‘just’ come in contact with it.

Leave a Reply