Pharmacies sell unrefined castor oil, which when mixed with dishwashing liquid and water in a blender forms a natural mole repellent, according to the Washington Department of Fish and Wildlife. This mixture has similar results to castor oil pellets available at some garden supply stores.
Regardless of the castor oil product the property owner selects, he applies it to the ground and then irrigates the area to water it in place, according to the Washington Department of Fish and Wildlife. It is sometimes necessary to reapply the product to cause the moles to move elsewhere. The solution normally remains active and keeps moles out of the area for up to two months.