A Herb of Mercury, and of Clear Sight

Culpeper placed fennel under Mercury, and it was among the plants long reputed to sharpen the sight and clear the head, a folk reputation recorded here as history, not as medical claim. In European folk practice fennel was a protective and strengthening herb, stuffed in keyholes to keep out ghosts on Midsummer Eve and hung over doors, and it was one of the nine sacred herbs of the Anglo-Saxon Nine Herbs Charm against poison and infection. Its seeds were chewed to quiet hunger during long church services and fasts, giving it a homely place in Christian as well as pagan folk custom.

Pliny records the belief that a snake, on sloughing its old skin, would rub against fennel and eat it to sharpen its sight, the origin of the plant's long reputation as a herb for clear vision, an idea repeated by herbalists for over a thousand years afterward and given here as recorded folklore, not as any claim that fennel restores eyesight. The same association made fennel a common ingredient of eye-washes in medieval and early modern medicine, a domestic practice with no basis confirmed by modern ophthalmology, though the plant's genuine value as a flavouring and digestive herb was never in question.