The Celtic Tree Calendar is based on the ogham alphabet and its association with trees.
It consists of 13 months, each 28 days long, following the lunar cycle, as Roman accounts have suggested the Druids did, with one extra day representing the 23rd December, the ‘Day of Creation’.
Each of the 13 months is represented by a tree together with its ogham letter.
The calendar was conceived by the British poet and scholar Robert Graves. It was an idea put forward in his book The White Goddess, a historical grammar of poetic myth, first published in 1948.
The book focused on the mythology of Ireland, Britain, Europe and the Middle East, interpreting it in Grave’s individual and poetic style.
As historical accounts of ancient Druids are scarce, many of Graves’ ideas regarding the Celtic Tree Calendar were based on the works of Irish historian Ruaidhrí Ó Flaithbheartaigh, (Roderick O’Flaherty). Ó Flaithbheartaigh had published Ogygia in 1685, an elaborate history of Ireland that journeys back to the time of myths and legends and contains within it a chapter on understanding the ancient ogham alphabet.
Graves’ works may also have been influenced by the 14th century Book of Ballymote which contains a chapter on the ogham in which many varieties of the alphabet appear in the form of several diagrams thought to be used as secret codes.
Although the calendar is quite new in a historical sense, its influences lie within ancient Celtic mythology and folklore. It is a beautiful example of how modern spiritual beliefs and the customs of ancient times can be combined to form something enchanting.