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The Celtic Tree Calendar – following the lunar cycle

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.

Celtic Tree Calendar. Image copyright Ireland Calling

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.

Book of Ballymote

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.

More on Celtic trees folklore




Trees in Celtic Mythology





Alder – balanced between male and female

Apple – healing, youthfulness and rebirth




Ash – one Ireland’s sacred trees





Aspen – sacred Celtic whispering tree

Birch – the tree of birth





Blackthorn – sinister tree of the dark side




Elder – a tree sacred to the Celts




Gorse – symbol of love and fertility




Hawthorn – the fairy tree




Hazel – the tree at the world's end

Heather – building block for Celts





Holly – guards against spirits and witchcraft





Ivy – symbol of strength and determination




Mistletoe – sacred plant of the sun god





Oak – king of the forest





Reed – introduction to Ogham





Rowan – the 'lady of the mountains'

Scots Pine – the 'pioneer' plant'





Vine – the tree of joy



Willow – beauty and spiritual presence





Yew – longevity and resurrection




The Celtic Tree Calendar – following the lunar cycle

Ancient Irish language of ogham

Ogham – ancient Irish written language





New age beliefs about Ogham





Ogham alphabet named after Irish words for trees




Origins of Ogham – modern theories





Poems written in Ogham

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