Skip to content

Celtic Tree Calendar · Month 4 of 13

Alder, the month of the letter Fearn

Alder is the fourth of Graves' tree months, 18 March to 14 April, led by the Ogham letter Fearn, F. Its Old Irish name fern genuinely means alder, and its kenning, the shield of warrior bands, is borne out by the one Iron Age shield that survives in Ireland.

Is this your tree month?

Enter your birth date to see your free Celtic Tree chart. No email needed.

Not saved, and never put in a web address. Privacy policy

The Ogham letter Fearn drawn upright on a stemline, three strokes to the right of the stemline, read from the bottom up; beside it the words Fearn, the Alder month, letter F, and the dates 18 March to 14 April. Fearn The Alder month · letter F 18 Mar to 14 Apr Old Irish fern Name means alder Read from the bottom up
Fearn, the letter F, as it is cut on the stones: three strokes to the right of the stemline, read upwards. Drawn by us from its Unicode code point, not from a font.

Facts

Tree month
18 March to 14 April (Graves, 1948)
Days
28
Ogham letter
Fearn, the letter F (U+1683, OGHAM LETTER FEARN)
Old Irish name
fern
The name means
alder
Letter and tree
The name means the tree
Kenning (Morann)
airenach fían, "shield of warrior-bands" (tr. Calder 1917, p. 277)
Medieval tree gloss
alder (Auraicept, Calder 1917, p. 91)
The tree in Modern Irish
fearnóg or fearn

Meaning

Alder grows with its roots in water, and its timber lasts when it is kept wet, which is why it was used for piles and foundations. The kenning of its letter is "shield of warrior-bands", in Calder's translation, and the Auraicept says why: "The van of the warrior-bands, that is, alder, for thereof are the shields".

Our reading takes steadiness under pressure from this: people born in this month are read as good at holding a line for others, with a strength that does its work out of sight. The reading is ours.

The letter

Fearn is the third letter of the stones: three strokes to the right of the stemline. Graves' calendar moves it to fourth place, behind Nion. Its Old Irish name fern genuinely means alder, one of the few letter names that is a tree. Both medieval tracts gloss it as alder, and O'Flaherty in 1685 adds that shields are made of it.

The alder shield

Here the medieval gloss and the archaeology meet. The National Museum of Ireland holds the one surviving Irish Iron Age shield, found at Clonoura, County Tipperary, and it is made of alder. That supports what the tract says. It does not show that alder was the main wood of shields everywhere, as some pages claim.

In Graves' year

Alder runs from 18 March to 14 April, the same in every list of the tree months. In another chapter Graves pairs the alder with Saturn among his trees of the week, and Paterson gives it a different planet; tree-sign websites add a gemstone, an animal and a personality title. All of this is modern, and we leave it out.

Correspondences

Each item with how it stands: “sourced” is in the work cited, “our construction” is EsoTerrier’s own, and “disputed” means the sources disagree.

The Auraicept's explanation
"The van of the warrior-bands, that is, alder, for thereof are the shields" (Calder 1917, p. 91) sourced
The Ogam Tract's gloss
the same tree (Calder 1917, p. 277) sourced
O'Flaherty's gloss (1685)
Fearn, the alder, of which shields are made sourced
How the letter is tied to the tree
The name means the tree sourced
Colour and bird words for the letter (a medieval curiosity)
Colour: flann, "red"; bird: faelinn, "gull". Words that begin with the letter, like the tract's lists of churches; not the tree's colour or animal sourced
Our reading
A tree with its roots in water: holding a line for others, with strength that works out of sight. our construction

How the schools read it

The medieval tracts
The kenning "shield of warrior-bands"; the Auraicept glosses the letter alder.
O'Flaherty, 1685
Fearn, the alder, of which shields are made.
Graves, 1948
The fourth month, 18 March to 14 April.
Ogham scholarship
fern is one of the few letter names that genuinely names a tree.
Tree-sign websites
The same dates; a planet, gemstone, animal and personality title, all modern. Not used here.
EsoTerrier
A tree with its roots in water: holding a line for others, with strength that works out of sight.

Claims about it

  • Alder was the chief wood of Celtic shields.

    unverified

    What the record shows: What is documented: the medieval tract says shields were made of alder, and the one surviving Irish Iron Age shield, from Clonoura, is alder. "Chief" goes beyond that.

  • The Alder month belongs to an old Celtic calendar that the Druids kept.

    false

    What the record shows: No ancient or medieval source has a tree calendar or a tree for each birthday. The thirteen months are Robert Graves', set out in 1948.

  • The Alder month has a traditional personality title.

    false

    What the record shows: The thirteen titles come from one website of the 2000s and were copied widely; nothing in Graves, Paterson or the medieval tracts supports them. We never use them.

  • The Alder month has a traditional planet, element, gemstone and animal.

    false

    What the record shows: Modern additions: the planets are Helena Paterson's (1992), the rest come from later web lists that disagree with one another. None is medieval or in Graves as a set.

Elsewhere on EsoTerrier

Sources

Primary texts (4)
  1. George Calder (ed. and tr.), Auraicept na n-Éces: The Scholars' Primer, with In Lebor Ogaim (the Ogam Tract). Edinburgh: John Grant, 1917. Quoted with page. archive.org/details/auraicept00calduoft
  2. Roderick O'Flaherty, Ogygia. London, 1685; English by James Hely, Dublin, 1793. archive.org/details/ogygiaorachrono00helygoog
  3. Robert Graves, The White Goddess. London: Faber and Faber, 1948 (revised 1952 and 1961). Facts only; not quoted.
  4. The Unicode Standard, Ogham block U+1680 to U+169F (encoded in Unicode 3.0, 1999). unicode.org/charts/PDF/U1680.pdf
Studies and other sources (10)
  1. Damian McManus, "Irish letter-names and their kennings", Ériu 39 (1988), pp. 127 to 168. jstor.org/stable/30024135
  2. Deborah Hayden and David Stifter, "Ogam and Trees", OG(H)AM project, 20 December 2022. ogham.glasgow.ac.uk/index.php/2022/12/20/ogam-and-trees
  3. "Ogham", Wikipedia (orientation only). en.wikipedia.org/wiki/Ogham
  4. Mary Jones, "Celtic Tree Calendar", Jones's Celtic Encyclopedia (2004). maryjones.us/jce/celtictreecalendar.html
  5. Christopher Penczak, "Celtic Astrology Tree Signs" (2013), crediting Paterson. christopherpenczak.com/celtic-astrology-tree-signs
  6. Helena Paterson, The Celtic Lunar Zodiac. London: Rider, 1992 (known from catalogue records and Penczak). search.worldcat.org/oclc/31606966
  7. whats-your-sign.com, "Celtic Tree Astrology", Wayback Machine capture of 28 February 2008 (cited only as the source of the claim). web.archive.org/web/20080228140902/http://www.whats-your-sign.com/celtic-tree-astrology.html
  8. Nora White and the Heritage Council, Our Ancient Landscapes: Ogham Stones in Ireland (2021). heritagecouncil.ie/content/files/Ogham-Stones.pdf
  9. National Museum of Ireland, the Clonoura shield. museum.ie/collections/collection/antiquity-15743
  10. Foras na Gaeilge, focloir.ie and teanglann.ie (Modern Irish forms). focloir.ie
Our own research (2)
  1. EsoTerrier, Celtic Tree research and validation, 11 to 13 October 2026.
  2. EsoTerrier calculation engine, the Celtic Tree Calendar service, its texts and its documentation.

Your Celtic Tree reading, $3.99. Includes this system's raw data. Written for you by AI. Read a sample. Charts and the written text are free in every account.

By EsoTerrier. Written with AI assistance from our research and checked against its sources; last revised 19 October 2026. How we write these pages.

First published ; last revised . Corrections: support@esoterrier.com.