I’m just going to get this out of the way: the Celtic tree calendar is kind of problematic. In fact, I don’t even really like calling it the Celtic tree calendar, simply because it’s not Celtic. The tree calendar was established in 1948 in Robert Graves’ book The White Goddess. The first flag you should be aware of is that Robert Graves was a poet not a scholar. The White Goddess, while an intriguing feminist manifesto of sorts, is in no way scholarly nor historically accurate.
That disclaimer aside, this does not mean that the idea of a tree calendar isn’t interesting. It’s just not Celtic…or ancient. The idea of the tree calendar was inspired by the writings of Edward Davies during the “Druidic Revival” of the nineteenth century. Davies, upon reading Ruairí Ó Flaitheartaigh’s (don’t even begin to ask me how to pronounce that) 16th century book Ogygia, suggested that the Celts might have had a 13 month lunar calendar. Graves ran with this idea and thus created the tree calendar, basing the months off of the ogham alphabet. This is in-and-of itself problematic, since the association of the letters with trees only dates back to the 14th century and Graves’ calendar is supposed to be of pre-Christian origins.
But, that’s not the only thing Graves got wrong. Though we know now that the Gauls, a Celtic tribe located in modern day France, did have a twelve month calendar called the Coligny Calendar, the months were not named for the trees. And though there is some argument as to whether the Gaul’s Coligny calendar began with November 1st or May 1st, it has been well established that the Celtic year began on November 1st which was marked by the celebration of Samhain. Graves’ calendar begins on December 24th. This was done to coincide, according to Graves, with the birth of the sun god (which would have to be Jesus, since the wiccan tradition celebrates the birth of the sun god on the winter solstice which can occur anywhere between the 20th and the 23rd of December depending on the year). Finally, the Coligny calendar had months of varying days to match the lunar cycle, however each month in Graves’ calendar is set to a rigid 28 days each.
All of this aside, like I said before, it’s an interesting idea. And since it has spawned all sorts of ideologies and mythos (some based in fact, some not so much), I look at it the way I do the Grecian zodiac: it’s interesting and fun to research. There are many neo-pagans and wiccans who follow the tree calendar and the tree zodiac, and, frankly, who am I to ruin it for them?