Yes, sunflower plants are toxic to dogs. If a dog eats the leaves of a sunflower plant, it can be poisonous.  They are not safe either to our furry friends. The reason why they are not safe for dogs is that they contain some fatty acids that can cause pancreatitis, a condition that can damage the pancreas. Sunflower seeds are also not good for dogs, but luckily they are not as harmful as plants. Sunflower plants can cause a number of side effects to your dog. They can include vomiting, diarrhea, and even death.