Capable Canine Tips Tips Archive   Poisonous Winter Plants Certain common winter plants could cause trouble for dogs.Poinsettias, holly, and mistletoe are all no-no's for your pet. If ingested, poisettias could give your dog a bout of mild to moderate gastrointestinal   upset. Both holly and mistletoe are highly toxic and could be fatal if eaten. Keep your pet feeling fine this season by placing these plants out of reach so he or she is not tempted to explore them.