Because horses are natural grazers, many people don’t know that seemingly benign vegetation might be dangerous.

Take grass clippings, for example. They’re so tasty that horses may bolt them down, risking esophageal obstruction. What’s more, their high digestibility causes rapid hindgut fermentation that could result in laminitis. Clippings that mold in wet weather can also increase the risk of colic.

Trimmings from certain shrubs and trees are highly toxic as well. Yew tops the list, but rhododendrons and azaleas are poisonous too. Oak and red maple are also dangerous, and there’s a long list of toxic ornamental plants and weeds.

So, be sure to do your research—and then caution your family, neighbors and gardeners not to treat your horse to anything you haven’t approved.