Ha! Poison. It's about as ineffective as it is inhumane. Rats and mice breed much too prolifically and you assume that one will go for the poison as opposed to the plant; or that one that goes for the poison would have gone for the plant.
You'd be better off using other deterrents like cat fur or urine, peppermint oil or some other natural repellent. A tin can with both ends removed and buried a bit into the soil can also help protect the main stalk from potential rodent damage as well as other pests.