Nothing mystical, nothing paranormal. Just a tractor, some seeds and imagination. From the wide plains of Kansas, and now, for the first time, to an English hillside, American crop artist Stan Herd creates giant 'earthworks' that blend agriculture, art and a love of landscape. By Sharon Amos
Rail travellers on the London to Birmingham line who look up from their newspapers may have noticed a surreal imposition on the landscape: just outside the Buckinghamshire village of Cheddington, a field of wheat has sprouted into the shape of a giant beer bottle. Not the mysterious work of aliens, but of one individual - Stan Herd from Kansas, USA, the "world's leading crop artist". The challenge of working on a hillside - a rare opportunity for a man from the plains of Kansas - and the temptation of a milder climate had been sufficient to lure Herd across the Atlantic for the first time.

Now, as he stands almost waist high in wheat, inspecting the fruits of his year-long project, he has difficulty believing what he sees. "Is wheat always like this over here?" he asks wistfully. "If only I could take some home to show my father."

Stan Herd has deep family roots in farming. "My grandfather came west from Missouri in 1916 in a covered wagon and homesteaded the land. My sister, four brothers and I grew up on the farm. We were like the Waltons. Eventually, when I moved to the city, I found most of the population didn't live like that. I guess I was a little naive ..."

Farm life was tough and, in order to escape the heartbreak of drought and unpredictable hailstorms that could destroy an entire crop overnight, Stan Herd enrolled at art college in Wichita, Kansas. It was the late Sixties, the American Indian Movement was growing and finding sympathy among young Americans of all denominations. Its resonance was to make itself felt in Herd's work.

Flying into Dodge City one day he was struck by the sight, far below, of a solitary tractor drawing in a sweeping arc a dark furrow across the landscape. It proved the inspiration he sought. From that point on, Stan Herd determined to work on the land itself, to bring agriculture and art together by creating a giant art form on the earth, making use both of the land and the crops growing there.

He began with a portrait of local 19th-century Kiowa Chief Satanta, to be etched on the Kansas plains like a copperplate engraving. But only after five years of persuasion and persistence was he able to walk out onto a 160-acre wheat field and start plotting the co-ordinates of a grid system that would enable him to transfer his sketch on to the land. Marking out the grid took a team of workers seven days and ploughing the basic outline took Stan Herd most of the day. "At the end of that day I headed for the airport to check the results. It was an incredible feeling as we slowly approached the image at 1,000ft to discover that the outline perfectly mimicked my original drawing."

A succession of designs followed, using both the earth as a medium to be scored and scarified like a lino-cut, and planting local crops for colour, texture and relief. In each case, consultations took place with farmers and agricultural advisers on soil and local geography. But nature always insisted on playing the wild card. A 160-acre portrait of writer and humorist Will Rogers was unexpectedly seared to browns and rusts after a 20-day heatwave scorched the maize it was planted with; while a year's work was destroyed in minutes when the wind veered and a controlled prairie burning used to etch the outline of a young Kickapoo girl suddenly raged out of control.

Crop art is not to be confused with crop circles. A New York crop circle specialist rang Stan Herd when a batch of mysterious designs appeared last summer. "She said, 'It's you, isn't it?' When I said no, she replied, 'Well, you're involved psychically, whether you like it or not.'"

Most of Stan Herd's earthworks are in remote spots. Farmers who have donated land tend not to

be keen on sightseers, and anyway the image is not designed to be viewed from the ground. Siting them beneath an air route makes some sense, though visibility is not that much of a priority as we can all have access to his work via photography.

At first, it didn't occur to Herd to preserve on film anything other than the final image. Any interim photographs were simply used as tools, to be drawn or scribbled on to decide the next stage. But when he began work on Sunflower Still Life in the mid-1980s, simplified from one of his own paintings of a vase of sunflowers and a patchwork quilt - the aerial photographer Dan Dancer suggested he record the work in progress. The result was a series of beautiful and unexpected images that no one - Herd included - would otherwise have seen. Photographs of the final image, with plantations of sunflowers themselves forming giant flower heads, are compelling. And when you spot in the frame a tractor that's barely one-tenth the size of a single leaf, then the scale of the project becomes truly awesome. It's difficult to imagine how one man could hold an overview like that in his head while working at such a lowly level, ploughing the outline of a flower hundreds of yards across.

Almost without exception, Herd's work is ephemeral; farmers who've lent him land eventually want to re-use it. And, anyway, the crops used are seasonal and sooner or later die. There's also a curious blurring between the boundaries of agriculture and art as the plantings are sometimes harvested and vegetables picked. But he has no regrets as an earthwork returns to the earth. "Any permanent stuff would be too much like landscape architecture - why impose on an already beautiful site? And imagine what would happen if everybody who had the inclination went out and covered the countryside?" He concedes, though, that there can be a place for permanent image, perhaps to disguise ugly landfill sites or where planting might halt erosion.

He has, in fact, been persuaded to create one permanent earthwork - a portrait of Amelia Earhart, the first woman to fly solo across the Atlantic, in her home town of Atchison, Kansas. Fifty tons of local limestone in varying shades have been used to highlight her features; 500 indigenous juniper bushes form her flying helmet, while the native big blue stem, a grass that grows to 6ft ripples in the wind like a real scarf. "It was a helluva project. It really wore me out. It was a very expensive endeavour, too." And he's not at all sure that's the direction he wants his work to go.

On the face of it, his UK project seems simple by comparison, but there is more to it than meets the eye. The 600ft bottle, commissioned by Beck's beer, is created on a slope, so to compensate, the image has had to be manipulated and stretched so that it appears in proportion when seen from the train or air. The 9,000 red salvia that border the bottle's label had to be protected by an electric fence or hares would have stripped the plants in a day. "It's a gamble - but then all agriculture is."

At least in the damp early British summer the plants established well. "Yes, I've been spoilt now. It'll be hard to go back to the dry lands of Kansas." There's also a far greater palette of plants for a crop artist to use here - linseed, oilseed rape and flax have all caught his attention and captured his imagination.

Future plans include an earthwork in Australia for the millennium Olympics (no, the recently discovered giant hunter etched into the outback was not his doing). And he can't stop thinking about that very European eccentricity, the maze. Let's hope he returns to confound us again

Stan Herd's Beck's beer bottle can be seen from the London Euston to Birmingham mainline, on a hillside just south of Leighton Buzzard (out of the train's left-hand side if travelling from London). 'Crop Art and Other Earthworks' by Stan Herd is published by Harry N Abrams Inc, and distributed in the UK by Thames & Hudson, price pounds 12.95.

Turn your garden into a work of art ...

The basic principles that Stan Herd uses to create his earthworks can be put to good effect in an ordinary garden, albeit on a fraction of the scale. It's possible to make something that will look brilliant from an upstairs window, yet can be appreciated at ground level, too. Here are Stan Herd's tips for doing it yourself:

1 Choose a simple, graphic image. Complex shapes will be too difficult to work with. For example, you might consider using a motif from one of Stan Herd's recurring backgrounds - the patchwork quilt.

2 Transfer your chosen image to a grid, to break it down into easily copied components. The scale you use will depend on the size of your garden and the area you plan to turn into an earthwork. In the average garden, a scale of one inch representing one foot seems reasonable. Draw up the grid on tracing paper and enlarge or reduce your image as necessary on a photocopier. Lay the grid over and trace off the image.

3 The next step is to mark out a full-size grid in the garden using pegs and strings. Then copy each portion of the image into each square. Do this freehand by drawing lines firmly in the soil with a sharp stick, for example, or by trickling a line of sand from a bottle or plastic bag with the corner snipped off. Check how the outline looks from an upstairs window, and once you're happy with it, take up the pegs and string.

4 Use a mixture of organic and inorganic materials to fill in your earthwork. Stone, gravel and bark chips are ideal, with plants adding colour and light. You'll have most success if you choose fairly robust species. Important aspects to consider are the contrast between materials, their texture and colour.

5 According to Herd, this kind of earthwork has to be pleasing from the ground but must be created with a high vantage point in mind. One of his few small-scale works is Worked Patch, a 'quilt' of wheat, flowers, stone and wood, whose design is only truly revealed from the upper floors of a building at the University of Kansas, yet whose flowers can be appreciated at ground level.

6 Enjoy the different appearance your earthwork takes on as petals fall,

leaves change colour and bark chips take on a dusting of frost. Clip back plants from time to time to keep their shape and tidy up gravel to keep lines true - or just sit back and let nature take its course.