The renowned German artist Nils-Udo has been transforming Connemara into Earth art. Lorna Siggins visits his installation

'Sketching with flowers. Painting with clouds. Writing with water . . . Working for a thunderstorm. Awaiting a glacier . . . Setting fire to the fog and the perfume of the yellow barberry . . ." These are the words of the renowned German artist Nils-Udo on his working life - and after several weeks of weathering west Co Galway, his experience with peat, gorse and Connemara lakes may inspire further lyrical descriptions.

Earlier this month, the Bavarian braved rain and gales to complete a most ambitious project as part of this year's Galway Arts Festival. Clochar na gCon, a spectacular bog running up over Indreabhan and down towards the Atlantic, was his "studio" for most of that time. With the assistance of a team of artists, Nils-Udo took materials, moulded and shaped them, then recorded the work on camera. These images of his installations, as he calls them, will be transferred onto aluminium and exhibited at Galway Arts Centre during the festival, in July.

Born in Lauf, a small village in Bavaria, in 1937, Nils-Udo trained and first worked as a painter. In 1972, however, at a time of growing environmental awareness, he turned from painting nature to creating site-specific pieces with natural materials. "At first I began working alone in the forest near my home village," he says. "I rented land from farmers and planted trees, and shaped the earth. Sometimes I would photograph what I had made, sometimes I would make silk-screen prints, and most of the time people didn't quite know what I was doing."

He is regarded now as one of the founders of the Earth-art movement, and his work has appeared in Europe, Japan, Israel, India and Mexico. The world is his canvas: a catalogue published in 1999, which includes collaborations with the musician Peter Gabriel, moves from images of fern leaves in an Austrian lake to a child in a tree on the island of Réunion to a tower of rushes on the Aegean Sea in Greece.

When he arrived in Galway, Nils-Udo drove several hundred miles with Fidelma Mullane, a heritage consultant, and Paul Fahy of Galway Arts Festival, before chosing his locations. "I like to respond to what I find. I arrive completely free and open," he says. "I am fascinated by peat, as I have never worked with it before."

Locals weighed in behind the project, which was funded by Foras na Gaeilge, Údarás na Gaeltachta, Conradh na Gaeilge and the Arts Council. Comharchumann Shailearna gave permission for use of the bog, and Joe Hogan, a basketmaker at Loch na Fuaidhe, provided willow. Michael Peril of Coonagh in Co Clare, on the Shannon estuary, gave the artist reeds, while Patrick McCormack, a farmer on the Burren, provided hazel rods and Brian O'Driscoll brought in sandstone.

Then Nils-Udo was given lessons in how to use a sleán, then found himself knee deep in bogholes as he created images within the bank, including a perfect set of stairs and a series of cavities filled with balls of wet clay, or "poor man's turf". Down in Rossaveal, he filled derelict cottages with carpets of gorse, unaware that gorse was once linked to the protection of homes.

"I've worked on vernacular architecture here for 20 years, and yet he would walk in to a place and capture the soul of it," says Mullane. "He has that natural artist's instinct, which is a very special gift. He was also particularly aware of the influence of the Irish language and was very precise in terms of gathering place names in Irish wherever he worked."

His aim is to "highlight the ordinary" and to "rescue nature from obscurity". Mullane believes the world in which Nils-Udo moves and works is reflected in an eighth-century Irish poem that defines the pre-Christian cosmos: "muir mas, nem nglas, talam ce." This translates as "the beautiful sea, the blue heaven, the present Earth".

A group of artists gave their time to work with Nils-Udo, including Frances O'Connor, Miriam Donohue, Elizabeth Porritt, Aideen Barry, Sven Verner, Linda Kavanagh, Louise Manifold, Podge Daly, Nicholas Devaney, Valerie Joyce, Mike Smith, Dermot Mullen, Eanna de Buis, Tim O'Connell, Louise McVey, Sibéal O Cumin, Jennifer Cunningham, Sean O'Flaherty, Allan Cavanagh, Briain O Driscoll, Bryan Maye, Chris Lillis, Mike Crawley and Lona Phillips.

They worked with him in the knowledge that each piece would be left to the elements after his final photograph.

Nils-Udo wants to return to Ireland to make a "book" on the Connemara lakes, such as that at Clochar na gCon, which he framed with hazel, willow and pine needles to create a set of "curtains" for his photgraph. "I take the light, the weather, the tools and the assistants. We work a long day, and then everything is done for that moment of the photograph."

Nils-Udo emphasises that he is aware of the basic contradictions inherent in his work, even if he works parallel to nature and intervenes only with the greatest possible care.

"It is a contradiction that underlies all of my work, which itself can't escape the inherent fatality of our existence. It harms what it touches: the virginity of nature . . . To realise what is possible and latent in nature, to realise literally what has never existed, utopia becomes reality. A second life suffices. The event has taken place. I have only animated it and made it visible."