Horses can eat carrots, peas, green beans, lettuce and squash. Some other vegetables that horses can eat include beets, celery, pumpkin, parsnips and cucumbers. They can also eat corn, plantains and a variety of dried beans, such as pinto, fava and red beans.
Vegetables such as Brussels sprouts, collard greens, chard, kale and broccoli should only be given to horses in small quantities. The same goes for turnips, spinach, radishes, garlic and onions. Large quantities of garlic or onions may cause a horse to become anemic.
Horses can also eat rhubarb stems and the meat of avocados in small amounts, according to Rutgers University Cooperative Extension service, although the remaining portions of both vegetables are toxic to them. The ASPCA believes that horses shouldn't be fed avocados at all. They should never be fed tomatoes, any type of pepper, potatoes or sweet potatoes.
Although horses can eat a wide variety of vegetables, what they eat is determined by their personal taste. Vegetables should be fed to horses as a regular part of their meal, in addition to 1 to 2 pounds of feed. The vegetables can be mixed with the feed or fed to the horse separately. If horses are being introduced to a new vegetable, only small amounts should be given to them at first to check for an allergic reaction.