Has ever a plant inspired such love and such hatred as the rhododendron? Its beauty is inarguable; it can clothe whole hillsides and gardens with a blanket of vibrant color. The rhododendron has a propensity towards sexual infidelity, making it very popular with horticultural breeding programs. And it can also be used as an herbal remedy for an astonishing range of ailments.

But there is a darker side to these gorgeous flowers. Daphne du Maurier used the red rhododendron as a symbol of blood in her best-selling novel Rebecca, and numerous Chinese folktales link the plant with...