If you have the kind of dog who views everything within reach as a potential snack, you should be careful about what kind of air freshener you use. Dry potpourri can be a fragrant addition to a room, but it can also lead to an upset stomach or worse if your dog decides to sample it.
Dry potpourri is made up of a wide variety of fragrant items, many of them dried herbs and flowers of various types. The potential toxicity of such a mixture depends entirely on what plants are in it, but even nonpoisonous floral potpourri can irritate your dog’s gastrointestinal system and cause vomiting or diarrhea. If the potpourri mix includes harder items like miniature pine cones or bark chips, these could potentially lodge in your dog’s throat and cause breathing difficulties. Pine and other flora are toxic, but you might not be able to tell what each dried piece of potpourri is in a mix, especially since they're often artificially colored.
Eating potpourri could trigger an allergic reaction in your dog, with possibly severe consequences. Generally, nontoxic potpourri ingredients may trigger only drooling, but toxic bits would escalate danger. The dog's size, age and health would come into play, as well. If your dog eats dry potpourri, no matter what kind it is, you should find the ingredient list of the mix and call your veterinarian for advice. Liquid or simmerable potpourri is more dangerous than dry potpourri.