What’s What With Toxic Plants


toxic plants and your horse

Do you know what’s what when it comes to toxic plants and your horse?

In the last warm days before the colder weather sets in, many people prefer yard work to house or barn work. What you plant in or around your barn and pastures, and how you dispose of yard waste, could negatively affect your horse’s health. Toxic plants, trees and shrubs can pose a serious danger to your horse, so do you know which ones to avoid?

Understanding Plant Poisoning

There are hundreds of plants in North America that can be poisonous to livestock. Poisonous plants contain toxins that generally have a bitter taste in order to keep the plant from being consumed. Animals are “trained” to avoid toxic plants by learning to recognize the smell or taste associated with the toxin. Fortunately, most healthy, well-fed animals will not eat toxic plants if they have access to good quality forage. But horse and livestock owners should learn to recognize toxic plants, and be aware of the symptoms they can cause.

The level of concern should be greatest when:

•Animals are undernourished.
•They do not receive adequate forage.
•Pasture grasses are no longer available due to overgrazing, drought or changing seasons.
•The plant is highly toxic.
•The toxic plant has been reported to cause poisoning in healthy animals.

Plant poisoning can be difficult to diagnose, since symptoms can range from mild irritation to death. The severity of poisoning depends on how toxic the plant is and how much was eaten.

Mindful Yard Work

Most horse owners may not be aware that various yard waste “trimmings” can be toxic to horses and other livestock.

In urban areas, neighboring homeowners are unaware that certain yard vegetative plants tossed over the fence can be deadly when consumed by horses. It is always a good idea to establish a good acquaintance with your neighbors and educate them on the toxic effect yard waste may have on horses and other livestock.

Perhaps the greatest risk comes from those who need a place to discard their yew bush trimmings. As little as half a pound of yew trimmings can be fatal to a horse. Poisoning from this evergreen ornamental bush can cause sudden death within 24 hours, though occasionally death may be precluded by respiratory difficulty, shaking or muscle weakness. There is no known antidote for yew poisoning.

Other common landscape ornamentals are rhododendrons and azaleas. All parts of these plants, but especially the foliage, contain poison; two or three leaves may produce a severe toxic reaction. Rhododendrons are more likely to retain green leaves year round than most other plants, and most toxicoses occur in the early spring when other green forage is unavailable.

Prevent Poisoning

Almost every pasture contains some poisonous plants, or is bordered by trees or shrubs that are toxic. While it is not always possible to eliminate all the plants that may be toxic, there are several ways of managing both plants and horses to reduce the possibility of poisoning:

•Keep horses healthy by maintaining a good nutritional program.
•Make sure they have a steady supply of forage (grass or hay).
•Identify poisonous plants and trees in and adjacent to the pastures. Many good reference books, websites and fact sheets are available. Your local Extension office may have people on staff who can help you. Remove or fence off toxic trees and shrubs.
•Remove broken branches from toxic trees that have fallen into the pasture.
•Do not plant trees or ornamental shrubs or plants near barns and pastures. Colorful ornamental plants are frequently toxic.
•Do not use forest and wetlands for turnouts. Many toxic plants grow in these environments. Manage grasses to maintain a healthy, thick stand that can compete with weeds. Fertilize, rest and rotate pastures when necessary.
•Mow pastures to reduce weeds.
•When necessary, eliminate toxic plants with appropriate herbicides.
•Do not throw garden or lawn clippings into pastures

Prevention is your best bet for keeping your horse from ingesting toxic plants. Monitor your pastures and the surrounding areas, maintain the health of your horses and turnouts, and be mindful when doing yard work. With these keys, you will reduce the chances of ever having to deal with a plant poisoning incident.

Potentially Toxic Plants

The commonly available trees, shrubs and plants listed below are often sold at nurseries, and pose a potential hazard to horses if planted in or around enclosures. If these plants are found to be desirable for landscaping purposes, it is important to position them well away from where horses can reach them. Furthermore, it is essential to always provide a balanced nutritious diet to your horses at all times, so they are not driven through hunger to eat unusual plant material.


Dr. Ann Swinker is the Penn State University Extension Horse Specialist.  extension.psu.edu/animals/equine

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