The list of toxic plants is long - yew, holly, lilies, foxglove, rhododendron, aloe...in fact, most plants can cause an upset tummy if enough is eaten. If you've ever seen your dog snack down some grass odds are good you've also seen it come back up! Usually signs of toxic plant ingestion are very mild but you should always be aware of these risks and take appropriate action to minimize your pet's exposure. If your cat likes to explore the flower bed you should NEVER plants lilies and if your dog hangs out in the orchard you should know that many fruit pits contain toxic chemicals. Also remember that many of the pesticides and fertilizers we use on gardens and lawns can be dangerous and cocoa mulch contains enough "chocolate" to cause problems - and it smells great making it very tempting for pets to eat!
Carefully monitoring your pet when he or she is in the yard or on walks is a great way to prevent ingestion of potentially dangerous plants, but if your pet spends a lot of time out and about in the yard or you are going to keep houseplants it is best to do a little research and choose pet-friendly plant species. A complete list of toxic plants can be found at the ASPCA website: http://www.aspca.org/pet-care/animal-poison-control/toxic-and-non-toxic-plants?&&page=3.
Happy (and safe) gardening!