The Celtic tree calendar - the alternative arboreal schedule

ALL calendars were created as a way to measure the passage of time by observing the movements of the sun and the moon. A year is quite simply how long the Earth’s orbit takes around the sun. 

In truth, although there are 12 months in our year, there are 13 lunar cycles over the 12 months and we put the clock right with a leap year. Calendars are one way of us connecting with the natural world around us and recognising the importance that trees have in our culture and environment. Let’s look at one based on trees.

The modern tree calendar is based on a concept that letters in the ancient Celtic Ogham alphabet corresponded to a particular species of tree.

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A tree calendar spans across different months and is also aligned to the cycles of the moon. Although it sounds ancient, the modern tree calendar may not be based on a Celtic one, but it does have origins in the old Celtic alphabet where each letter was said to correspond to a tree. A sprinkling of other plants has crept in too. 

By adopting a tree calendar, you are creating a way for a culture to align itself with the rhythms of the environment and link to folklore.

So what is the Celtic calendar and its associated alphabet and what has it to do with trees?

The ancient Celtic people used a lunar calendar in which each month was governed by a moon. Each month started when the moon was full and it was further divided into fortnights, or two-week periods. A dark fortnight followed a bright one, as the moon waxed and waned.

The Celtic Ogham alphabet. (Image: Getty Images/iStockphoto)

Although lost in the mists of time, this calendar likely has its origins in the ancient Ogham alphabet or cipher where each letter or sign is assigned a tree or plant name.

Ogham is an ancient Celtic writing system that was primarily designed to inscribe forms of this early tongue back in early mediaeval times, from about the 4th to 6th century AD. 

As detailed above, the modern tree calendar is based on a concept that letters in the ancient Celtic Ogham alphabet corresponded to a species or type of tree. For example, ‘C’ or ‘coll’ represents hazel, while ‘R’ or ‘ruis’ represents elder.

Each Ogham letter is made of one or more full or half lines carved or etched into a stone. As it is written and read from the bottom to the top of a central axis, trunk, edge or stem-line, it was reminiscent of the branches of a twiggy or bushy tree – hence the ‘tree’ label.

Many letters from the modern alphabet did not exist when Ogham was in use. It had fewer letters – maybe only 18 or 20. 

There are roughly 400 surviving orthodox inscriptions on stone monuments throughout Ireland and western mainland Britain. Many of the inscriptions are of a person’s name and ancestry or tribal affiliation – an early form of graffiti. 

My guess is that these inscriptions were likely carved into wooden posts or even tree trunks too but those have long since rotted away.

Hazel (5 Aug to 1 Sept) is thought to represent knowledge and intuition. (Image: Getty Images)

As an aside, for those with an interest in and who follow Druid horoscopes, this ancient cult boasts a list of trees and general characteristics that are governed by the date you were born. 
So let’s look ahead to what the new tree year holds in store for 2025.

2025: MONTH BY MONTH

The Celtic tree calendar kicks off on Christmas Eve. Let’s run through it.

• Birch Moon – 24 Dec to 20 Jan: Also known as the lady of the woods, the elegant birch tree looks its best in the winter months. Following the passing of the winter solstice or the shortest day on 21 December, it’s a time for rebirth, regeneration and looking ahead. 
• Rowan – 21 Jan to 17 Feb: In Scotland, rowans are or were often planted at the front of houses as they are known for their powers of keeping evil spirits at bay; but be warned that once planted a rowan should not be moved. They are associated with Brighid the Celtic goddess of hearth and home and protecting mothers and families.
• Ash – 18 Feb to 17 Mar: In British folklore, the ash was credited with a range of protective and healing properties with most of these related to child health. Similarly the Celts gave the tree the name of ‘Cradle of Life’. Ash is also a great firewood, burning for a long time with an intense heat, whether seasoned or green. Whether the rampant spread of ash dieback will create a blank in the Celtic Tree Calendar remains to be seen. 
• Alder – 18 Mar to 14 Apr: This tree represents strength as it bears both male and female catkins on the same branch. Alder is a nitrogen fixer and its ability to fertilise even the poorest soils has been used for millennia.
• Willow – 15 Apr to 12 May: This group of trees is associated with healing, growth, knowledge and nurturing. The sound that willows and aspens make in the breeze is meant to be elves whispering in the branches as people walked underneath. 
• Hawthorn – 13 May to 9 June: The hawthorn (spelt with or without an ‘e’) in May is a welcome addition to many country hedgerows and has an abundance of beautiful blossoms. It was called ‘Huath’ by the ancient Celts, and represents a time of fertility. It was believed that bringing hawthorn into your house invites bad luck as it did for blackthorn or sloe. 
• Oak – 10 June to 7 July: The oak is often the tallest, oldest and strongest tree in the forest, and as such has been revered and worshipped by many cultures down the ages. The wood is renowned for its strength and durability and carrying an acorn in your pocket is meant to bring good luck. Give it a try. 
• Holly – 8 Jul to 4 Aug: Although often associated with midwinter, this evergreen reminds us all year long about the immortality of nature, and Celtic chiefs would wear crowns made from holly. Hanging a sprig in your house is meant to ensure good luck and safety for your kin, and holly trees were often planted near dwellings to protect people from lightning strikes.
• Hazel – 5 Aug to 1 Sept: Hazel has long been the wood of choice for small wood products such as hurdles or walking sticks and is thought to represent knowledge, uniqueness and intuition. There are a number of ancient tales surrounding hazel.

With its many healing properties, elder (24 Nov to 23 Dec) is known as the poor man’s medicine chest. (Image: Tom Meaker)
• Vine – 2 Sept to 29 Sept: The vine was extremely important in ancient folklore because of the grape, and wine has been made and drunk for thousands of years. It represents harvest time, thanksgiving and the onset of autumn. It’s known as the tree of joy, exhilaration and wrath and is believed to represent strength, endurance and determination.
• Ivy – 30 Sept to 27 Oct: This plant symbolises fertility, and at Christmas the evergreen holly and ivy come together giving much needed greenery at this time of the year.
• Reed – 28 Oct to 23 Nov: The reed represents adaptability and being able to bend with circumstances rather than break. While not a tree, to the early Britains it was an extremely important commodity for warm, dry homes. These plants are associated with health and healing, knowledge and learning.
• Elder – 24 Nov to 23 Dec: Known as the poor man’s medicine chest, the elder has many healing properties. The branches contain a pithy core which make it the wood of choice for the making of whistles, pipes and other musical instruments. There are many references in folklore cautioning against sleeping under an elder and this may be due to the strong smell of the leaves which is known to repel flies.

And so we come full circle. Best wishes for 2025.