While castor oil has a lot of memories for older generations, it is now used by gardeners for purposes that your grandmother never knew about. 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 of the castor bean 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. (As an aside, don’t bet the farm on voles not liking it)
Anytime the ground isn’t frozen.
Water the ground before you apply it and then again immediately afterwards for 15 minutes or so to drive the product into the ground.
Homemade Mix For Moles
You can also pick up smaller bottles of castor oil from drugstores and mix it at 4-ounces of castor oil per gallon of water with a dash of liquid soap (critical) to ensure it sprays and sticks to leaves.
Soak the area as much as possible (not just a light spraying but a very heavy dose, you want the spray to hit the ground)
Follow the watering directions above for the homemade product as well.