Castor Oil
The short and sweet version is that castor oil is produced from the castor bean plant (Ricinus communis) and while the bean is poisonous, the refined castor oil isn't to humans.
Note it's the seed coat that contains the bulk of the poison.
Another interesting fact is that this plant is the host for the Common Castor Butterfly.
Why We Use It
The oil does however have a peculiar smell that is hated by rodents such as voles and moles.
There is some anecdotal evidence that squirrels, raccoons, skunks, and groundhogs also will avoid this fragrance.
Application
Anytime the ground isn't frozen.Water the ground before you apply castor oil and then again immediately afterwards for 15 minutes or so to drive the product into the ground.
You can get a concentrated form of castor oil right here
