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This is a contested gloss, and a badly strained one. Old Irish muin carries at least three unrelated senses — the upper back or neck, a wile or ruse, and love or esteem — and the Bríatharogam pull in three directions accordingly. Morainn mac Moín gives tressam fedmae, "strongest in exertion", which the glossator reads as the back and shoulders that carry the load. The other two kennings turn on trickery and on the voice. Whatever muin originally meant, none of the three readings is a plant.

The botany finishes the argument. Bretha Comaithchesa ranks twenty-eight trees and shrubs in four classes of seven, and every one of them is a native Irish wood: oak, hazel, holly, yew, ash, pine, apple; alder, willow, hawthorn, rowan, birch, elm, cherry; blackthorn, elder, spindle, whitebeam, arbutus, aspen, juniper; bracken, bog myrtle, gorse, bramble, heather and the rest. Vitis vinifera is not among them because it was not there. A tree-list compiled in Ireland by people who could see out of a window would not include the vine; a scholastic word-list compiled by monks reading Latin scripture very well might.

Wine itself did reach early Ireland — imported, expensive, and needed for the Mass. Mediterranean and Gaulish pottery on high-status sites of the fifth to seventh centuries, at places like Dalkey Island and Garranes, marks the sea trade that brought it. Small-scale monastic vine growing is recorded later in Britain and Ireland, always marginal and always for the altar.

So the vine's religious weight in Ireland is Christian, entirely and demonstrably. It is the vine of John 15 — I am the true vine — and the wine of the Eucharist. The vine-scroll, an inhabited tendril with birds and beasts among its leaves, is one of the standard ornaments of insular art, running through manuscript decoration and across carved stone crosses. When a medieval Irish scribe drew a vine, that is what he meant by it.

There is no Celtic vine cult of any kind. The Dionysian material that Graves brought to this month — the god of the vine, the loosened tongue, the harvest ecstasy — is Greek, and he knew it was Greek; his whole method was to treat the Mediterranean and the Atlantic west as one poetic system. Modern Celtic astrology inherited the Dionysus without the caveat.

Modern druidry generally reads Muin as prophecy and truth-telling, on the in vino veritas line. Some orders, uncomfortable with a non-native tree, substitute the bramble or the blackberry for this month — an honest fudge, and a revealing one.

Date	Event	Why it matters here
c. 4th–6th c. CE	Ogham inscriptions; M is one oblique score across the arris	The letter is ancient
5th–7th c.	Imported Mediterranean and Gaulish pottery on Irish sites	Wine arrives in Ireland by sea; vines do not
7th–8th c.	Bretha Comaithchesa ranks twenty-eight native woods — none of them a vine	The real Irish tree-list has no place for this month
c. 600–900	Bríatharogam: tressam fedmae and two kennings on wile and voice	The name means back, or trick, or esteem — not a plant
7th–9th c.	Vine-scroll ornament in insular manuscript and stone carving	The vine in Ireland is a Christian motif
c. 1390	Book of Ballymote glosses Muin as finemain, the vine	The gloss enters the record, late and scholastic
1948	Graves, The White Goddess	Vine assigned 2 September – 29 September, with Dionysus attached
1988	Murray and Murray, The Celtic Tree Oracle	Muin becomes a divination card
1991	McManus, A Guide to Ogam	Muin shown to have no secure tree meaning
1997	Berresford Ellis, "The Fabrication of 'Celtic' Astrology"	A Celtic historian names the problem for an astrological readership

The vine month contains the autumn equinox, around 22 or 23 September, three weeks in. As with the other solar points, the equinox was not a named festival in early Irish sources; the modern eight-festival Wheel of the Year that includes it was worked out in the 1950s and 1960s.

The span sits in the middle of the Irish grain harvest, between Lughnasadh and Samhain, and that is a real season with real work in it. It is simply not a season of grapes. Where the calendar wants a September fruit for Ireland, the honest answers are the blackberry, the sloe, the crab apple and the hazelnut — and the apple already had its own ogham letter, Cert, which Graves dropped from the cycle to get thirteen months out of fifteen consonants.

• Celtic Tree Calendar — the system, and the year it was invented.
• Hazel — the month before.
• Ivy — the month after.
• World Zodiacs — the other six systems in the celestial row.
• Religion — the wider religion section.
• Calendar — the live month grid.