Most orchids are not poisonous to dogs, although eating them may upset the dog's stomach. The lady slipper orchid is an exception that may cause dermatitis if it comes in contact with a dog's skin.
Fertilizers, pesticides and other products applied to the orchid may be toxic to dogs, so dogs should not be allowed to eat orchids. However, accidental consumption is generally not a cause for concern. The ASPCA considers all orchid varieties to be non-toxic and safe for dogs. However, dogs that eat orchids should be monitored and taken to the vet if they develop allergy symptoms more severe than a mild stomach upset.