Plants can also pose a threat to dogs. Here's a list of some common plants that can be toxic. I was surprised to learn from a colleague that hosta plants can cause severe gastroenteritis. Her schnauzer ingested some and had a severe reaction.
If you notice vomiting or diarrhea and suspect that your dog has ingested something poisonous, don't hesitate to call your vet. It will be important to take a sample of what was eaten and approximately how much was consumed.
You can induce vomiting if requested by your vet. The recommended emetic is hydrogen peroxide, 3% orally at a dose of one tsp. per 10 lbs of body weight.
It's a good idea to order a book on canine first aid that includes a section on dealing with poisoning. I keep the book and an epipen on hand at all times.