The Mexican marigold (Tagetes minuta) is a malodorous plant widely used in companion planting for its ability to repel pests. Companion planting is an example of an organic control method. And adventurous landscapers desirous of controlling moles the organic way don't have to settle for planting the commonplace marigold. A couple of "living mole repellents" have a decidedly exotic flair: namely, mole plant and castor bean.
That's right: one of these plants has gained such notoriety as a living mole repellent that it is often referred to simply as "mole plant." Also called "caper spurge" (Euphorbia lathyris), this plant is an annual but re-seeds itself readily. Mole plant has a striking architecture and is often grown as an ornamental, standing erect and bearing lance-shaped leaves. Its leaves are marked with an exquisite white vein running right down the middle. If you make a cut into a mole plant's stem, a milky sap will ooze out, as when you break the stalk of a milkweed plant. It is apparently the smell of this poisonous, caustic sap that repels the moles.
The final living mole-repellant I'd like to describe is castor bean, also known as castor-oil plant (Ricinus communis). This one's a bit of a no-brainer, since, as I have already mentioned, commercial mole repellent formulas are based on castor oil. Used in the old days as a laxative, there are still many folks out there who can attest to the repellent qualities of castor oil. And it would seem that moles do not like it any better than humans do! A word of caution: castor bean, like mole plant, is poisonous -- neither should be grown around small children.
In temperate climates castor bean is treated as an annual. It grows quickly and can reach 15' in height, suggesting another use for this plant as well: namely, as a privacy screen for those who don't have time to wait years for a shrub to reach such a height. Castor bean bears huge, star-shaped leaves that make it a very attractive specimen, and thus desirable even on landscapes not plagued by moles.