Some types of ferns are poisonous to dogs. According to Vet Street, the most common threat comes from asparagus ferns, which contain sapogenin. Dogs that eat the berries of this plant are likely to undergo abdominal distress.
The asparagus fern is a common houseplant, as it is hardy and easy to maintain. Unfortunately, dogs are often attracted to these plants, and may try to eat them or rub against them. Paws Dog Day Care points out that when dogs eat this plant, they experience diarrhea, vomiting and pain; most cases pass within a day or two. However, dogs with severe symptoms should be taken to a veterinarian. Dogs with sensitive skin may develop skin irritation or a rash from contact with asparagus fern, even if they do not ingest it.