Denise Seghesio Levine, UC Master of Napa Master Gardener Column says, “Keep dogs away from hollyhocks, however. I have read several reports of dogs occasionally digging up and eating hollyhock roots with resulting trips to the vet. These are anecdotal tales, but worth paying attention to.” Also, be aware that hollyhocks can irritate the skin. This can happen to pets as well as humans. Despite these warnings, ASPCA lists hollyhocks as being non-toxic to dogs, cats and horses.