"I was walking along a road, here in the Borders, when I saw a horse on a hillside at dusk," says Aonghas MacNeacail. "A white horse, fading like a ghost into the greying landscape."
"On that occasion the trigger came to me in Gaelic, so I wrote the poem in Gaelic. But it can come just as easily in English.
"When I start writing, the trigger language is the one that I follow.
Getting a poem right is the hard part, anyway, not the language you use.
"I tell people you have to draft and redraft, and that doesn't mean writing out neatly. It means changing what you have written."
This is one lesson Mr MacNeacail has been trying to convey during workshops he has been giving as writer-in-residence at the first Mull and Iona Tree Festival, which runs throughout July.
The heart of the two-month festival, organised by the Tobermory arts centre, An Tobar, is the stunning exhibition The Tree Alphabet of the Celts, featuring poetry by Mr MacNeacail and images by artist Simon Fraser.
Rich, evocative and full of educational stimulus and opportunity, the tree alphabet belongs to an oral tradition used by scholar-poets as early as 1500BC, explains Lee Hendrick, An Tobar's visual arts and crafts officer.
"Through a series of word workshops, Aonghas has been bringing this hidden language of the Celts to local schools and community groups. The aim was to engage children actively in language through trees, their applications and folklore."
Primary pupils have been taking part, as well as French, English and Gaelic medium students at Tobermory High.
"Aonghas had already been to the school to talk to our second years about the Celtic alphabet and its folklore," says Margaret MacNeilage, an English teacher at Tobermory High. "We decided to focus on the birch tree, so we went down to the local park for an afternoon and were shown around by the ranger. The kids got down on hands and knees, picked out wee bugs and used their eyes and ears, their sense of smell, touch and taste. They really enjoyed that, even though we got eaten alive by midges."
Pupils were then asked to think up descriptive words for the birch and its environment, explains Ms MacNeilage. "For Aonghas's second visit, he took one word from each child, wrote it on to a leaf and stuck these on a large sketch of a birch tree. Then the pupils came up in pairs and arranged the words into lines that captured some aspect of the tree."
This was a fascinating experience for everyone, says Mr MacNeacail, including himself. "It was a bit like a visual manifestation of how I'd write a poem. You assemble the words you think you might need and start using them. Then you realise you need more and reach for the dictionary."
Having created the initial spark of a poem and the first draft, it remains for the pupils to redraft the work after he has gone, he says.
"Some of that first draft was very vivid. Children have a wonderful freedom with language.
"I see my role in this as encouraging young people to trust their experience and imagination. I want them to know that every one of them has something to say and the right to say it."
Douglas Blane www.treefestival.co.uk
coille'n aibidil dh'eirich craobh is dh'abair i rium bha litir na bial - a samhla
cha mhis an tus ars a chiad chraobh cha mhis a chr och ars an litir mu dheireadh
an alphabet forest a tree arose and spoke to me a letter in her mouth - her likeness
i'm not the beginning said the first tree i'm not the end said the last letter Aonghas MacNeacail