With gardening season upon us, many people also are starting to think about landscaping their homes and farms. Often, landscape plant choices are based on aesthetics and hardiness. However, with horses in the mix, plant toxicity is perhaps a more important aspect to consider. Even if owners plant trees, shrubs, and flowers well out of pastured or stalled horses' reach, the animals could still be exposed. Strong winds, storms, and flooding, for instance, can carry branches and other plant materials into pastures. Horses also can escape from confinement and gain access to areas normally out of reach. Garden workers might discard plant trimmings in pastures, unaware of how toxic some can be. Additionally, many farms have resident dogs and cats, so companion animal exposure to farm landscaping must also be considered.
Below are some landscape plants that should be avoided on horse farms if possible. Give this list to landscape architects and gardeners before starting landscaping projects. For those farms with established landscapes, compare the below information to a list of existing plants to determine if removal or replacement of plants is warranted. Consult with your veterinarian or a veterinary toxicologist experienced with horse poisoning for more information on the risks associated with various garden plants and trees. The list below is intended for use in the Bluegrass region of Kentucky and surrounding areas. It is by no means all-inclusive but includes some of the more common and important plants that could pose a toxic risk to horses or farm dogs and cats.
Trees to avoid on horse farms include: Red maple, wild cherry, black walnut, black locust, oak, Kentucky coffee tree, buckeye, golden chain tree, mimosa, persimmon, chinaberry, tung nut, and cycad palms.
Shrubs to avoid include: Japanese or other yew (Taxus) bushes, privet, common box, elderberry, Carolina allspice, choke cherry, serviceberry, buckthorn, fetterbush, laurel, and day-blooming Jessamine. Taxus bushes are especially toxic and ingestion of discarded Taxus hedge trimmings is a common cause of death in horses.
Flowering garden plants to avoid include: Delphinium, lily of the valley, foxglove, rhododendron and azaleas, lobelia, sweet pea, castor beans, bulbs such as autumn crocus, lilies, iris, hyacinth, amaryllis, and daffodils; poppies, morning glory, bleeding hearts, pieris, lantana, lobelia, ground cherry, angel's trumpet, periwinkle, monkshood, harebell, hibiscus, clematis, star-of-Bethlehem, bracken fern, rosary pea, baneberry, pheasant's eye, Lords and Ladies, begonia, butterfly weed and other showy milkweeds, yesterday today and tomorrow, caladium, diffenbachia and philodendron species, moonflower and other Datura species, sesbania, honeysuckle, may apple, and blue indigo.
Vegetable and crop plants can also be toxic to horses and other animals if accidental exposure occurs. Crop gardens should be well-fenced to prevent animal access. Garden crop plants that can be toxic include onions, chives, garlic, shallots, rhubarb, turnips, potatoes and tomatoes (leaves and green fruits), tobacco, and avocados.
Many weeds are toxic to horses and other animals. Garden weeds can pose a risk to horses if discarded into pastures. Some mulches also can pose risks to animals; avoid black walnut mulches and cocoa hull mulches in particular. Additionally, discuss risks of toxic plant exposure with neighboring property owners so they do not unintentionally poison your horses by discarding garden trimmings into your horse pastures.
This list is not all-inclusive and does not include important toxic plants that are not typically grown in the Bluegrass region (for example, oleander is an extremely toxic plant that causes many equine deaths in southern states but is not typically found in Central Kentucky). As with other toxicants, intoxication depends on exposure dosage. Consult with your veterinarian or a veterinary toxicologist to determine if your garden plant choices could pose a risk to horses or other animals.
Cynthia Gaskill, DVM, PhD, clinical veterinary toxicologist at the University of Kentucky Veterinary Diagnostic Laboratory, provided this information. Contact information: phone 859/257-7912; e-mail cynthia.gaskill@uky.edu.
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Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.