Toxic Trees and Horses


While horse keeping is hard enough, you also need to think about all of the toxic trees and horses. Most trees are just fine to have around horses, and others pose horrible risks that can end in much suffering, laminitis, and worse.  Identification of the trees and bushes and plants around your horse is critical, so you know what things need to be removed.

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Red maple trees


  • This is definitely one of the most famously dangerous trees for horses. We are just starting to understand that other species of maples may also harbor the same poisons, but in differing amounts. Red maples are a sight to behold, with bright red or yellow leaves in the fall. Beautiful, yes, dangerous, yes.


  • As far as we know, gallic acid is the dangerous part of the red maple leaf. There are likely other toxins, as well. A green leaf on the tree is primarily made of water, which dilutes the gallic acid intensity of that leaf.


red and yellow leaves on the ground
So many nopes.


  • As seasons change, the water disappears and the gallic acid concentration increases. Other factors, like the age of the tree, the type of maple tree, climate, etc. are also thought to affect the concentration of gallic acid.


  • The main problem is that horses find eating these maple leaves to be really delicious! Even as little as a pound of leaves can cause damage to your horse. That seems like a lot of leaves, but have you ever seen a horse casually stop eating something delicious? They just don’t.


  • If the gallic acid from maple leaves ends up in your horse, you can expect to see a myriad of symptoms as the toxins do damage.


  • Horses act like they have colic, become sluggish and tired, and usually stop eating once the toxins kick in. Your horse’s gums will darken and become discolored, his urine will be dark or black, and his pulse will be rapid.


  • The gallic acid destroys your horse’s red blood cells and sometimes causes them to break. In either situation, those red blood cells are not carrying oxygen. This leads to a chain reaction in your horse that damages the kidneys and creates anemia. If you start to see these signs that your horse has eaten maple leaves, his chances of recovery are slim. There is no cure, only treatment with fluids, blood transfusions, and support.


  • Your vet must visit if you catch your horse eating red maple (or other types) of maple leaves. Early intervention is vital.

More on maple trees here



  • Yews are actually a hedgy type plant or a smaller type of tree-looking plant. Usually, they are used as decorative plants in a landscape. Alkaloids are the lethal factor in the yew, and usually kill a horse (or another animal) within about 30 minutes of eating. Even a tiny amount of nibble is toxic.


  • It is understood that the yew’s concentration of alkaloids is most significant in winter, which unfortunately also correlates to the yew becoming even tastier to horses. The plant is also still toxic after it’s been cut and dried out, so the removal of yew plants and trimmings needs to be closely monitored.


  • You will usually never see signs that your horse is sick, as death happens rapidly. You may observe neurological-type signs, like paralysis, clumsiness, tremors, breathing trouble, and collapse. Given that the window between eating and death is so small, your best bet is to find another decorative shrub around your horses.


yew plant toxic to horses

Yes, the yew resembles hot pink plastic olives.


Black walnut trees


  • These trees can cause all sorts of problems even if your horse only stands on wood shavings that contain black walnut. Your horse can be poisoned by eating black walnut leaves, fruit, bark, shavings, and even pollen. Which, honestly, is one more reason to despise pollen.


  • Juglone is a toxic compound in black walnut trees. It’s more densely concentrated in the bark and wood than the leaves.


  • When a horse comes into contact with black walnut, the first signs of trouble look like laminitis and colic. The laminitis can develop within minutes of standing on black walnut shavings, and this laminitis is paired with swollen limbs. Most other types of laminitis do not have swollen limbs.


  • The first thing to do is get your horse out of those shavings and call the vet. The colic-like problems usually clear up after the source of the toxin is removed, but laminitis will likely be an ongoing issue.


  • If you are considering using a sawdust-type horse bedding from a local mill, be sure they don’t process black walnut trees.




  • Oleander, while beautiful, can easily kill your horse after snacking. The toxins are cardiac glycosides and are found throughout the plant. These glycosides interfere with the potassium levels in muscle and blood and cause a decrease in electrical activity across the heart’s muscle cells. The heart slows and eventually stops. This can take anywhere from 8 to 24 hours after an oleander snack.


  • There may be hope for the horse that has eaten oleander, but often the result is death. You might see that your horse has a fast and weak pulse, trouble breathing, is going into shock, is weak, and may collapse. Certain fluids and cardiac medications can be given but time is of the essence.



oleander flowers and blue sky

Oleander has long, flat, skinny leaves and oh-so-lovely flowers.

Wild cherry trees


  • The leaves and twigs of the wild cherry tree contain prunasin, which is a cyanide called prussic acid. When a horse eats this, it can be fatal. Wilted and stressed leaves are peak danger times when these toxins are at their highest levels!


  • When part of the wild cherry tree is eaten, your horse’s stomach acid creates hydrogen cyanide which quickly enters the bloodstream. Here, the cyanide prevents oxygen from getting into your horse’s cells, creating a backlog of oxygen in the blood and turning it bright red.


  • Horses will have trouble breathing, often with flared nostrils. Your horse’s pupils could be dilated, and convulsions, coma, and respiratory failure lead to death. There are treatments, and obviously, time is of the essence here.


Plum and Peach trees


  • These trees, while producing delicious fruit, are also members of the prunus species like the wild cherry trees. They also operate with the same toxins, creating cyanide in wilted leaves.


Oak trees


  • These giant trees pose a risk with their acorns, as they are chock full of tannins. Most horses find these treats tasty, and will definitely fight a squirrel for one. There are also tannins in the oak leaves and buds, as well, so that’s a problem.


  • The biggest issue with acorns, and I hear this from you guys a lot, is that small doses are usually harmless to horses. I get a lot of comments similar to “My horse eats them all the time and he’s fine!” That might be the case, but it might not be that way forever. Or he’s just sick enough not to feel well and hide it from you. My point is that just because it seems OK to eat toxic things, doesn’t mean it is.


  • The tannins in acorns mess with how proteins are metabolized in your horse. Ulcers, kidney failure, colic, constipation, diarrhea, and other GI problems are caused by acorn toxins.


  • No one knows how much of a dose is needed to severely harm a horse, which is a double problem as there’s no antidote, either. Like some other toxic trees, treating the symptoms and providing supportive care is all your vet can do.


oak tree in a meadow

There are LOTS of species of oak trees toxic to horses. And some don’t produce acorns for decades.


Horse chestnut and buckeye trees


  • The horse chestnut tree is rather poorly named, as no horse should ever eat any part of this tree. The tree is dangerous and poisonous when growing, the seeds, sprouts, and leaves all have toxins. Horse chestnut trees typically bloom first in spring, making them an attractive choice to chew on before other plants flourish.


  • The toxins are suspected to be the glycosides aesculin and fraxin as well as an alkaloid, possibly. Your horse, within a half a day or so, will develop neurological signs such as muscle weakness and twitching. Colic-like symptoms and pain will also appear, and coma could be the result leading to death.


  • Some horses can recover with help, like fluids and laxatives.


Practical implications of toxic trees around your horse


  • Know the trees on your property, especially so you can tell your vet if your horse becomes sick. Even “non-toxic” trees and shrubs and plants can cause a horse not to feel well, as those things are not part of his daily diet.


  • Enlist the help of an arborist or dendrologist to identify trees. Most tree services have one on staff. I’m attaching some websites where you can narrow down some possibilities and learn about identifying trees.


  • A tree service can professionally remove toxic trees, and collect debris from pastures and surrounding areas. For most tree removals, it’s not just as easy as chopping something down, roots and stump need to be killed and removed.


  • You may be tempted to leave some toxic trees up around parts of your farm that horses don’t visit. Please consider the wind carrying pollen, leaves, seeds, and branches to areas that horses can access. If a wind storm is powerful enough to rip siding from a house, it’s powerful enough to carry branches and leaves across a farm.



  • I often hear that poisonous plants taste bad so horses won’t eat them, but honestly, that’s bunk. Horses eat a lot of things that taste bad that are harmful, like buttercups! They also eat a lot of things that taste delicious and are harmful, like maple leaves and acorns.


Identification resources about toxic trees for horses:



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