In the hinterland of Edinburgh airport, between the M8 and the Forth, what looks like an enormous multicoloured weed has sprouted from a green lawn. It is visible from the road and, if you approach in the correct direction, from the air. On closer inspection, it is a huge steel aluminium structure, a floral totem pole by Marc Quinn.

Quinn, better known for putting a naked, pregnant disabled woman on a plinth in Trafalgar Square, is just one of the world-renowned artists whose work has, without fanfare or public funding, moved into this corner of West Lothian. Nicky and Robert Wilson have created Jupiter Artland in the grounds of Bonnington House, their home. It is what Charles Saatchi might have done if he had a love of the outdoors: a magical, personal collection of wonderful work, arranged by the artists in the couple’s 80-acre back garden.

These marvels — a Charles Jencks earth sculpture bisected by the driveway up to the house, a giant Antony Gormley figure called Firmament, Laura Ford’s Weeping Girls — are not just for the Wilsons and their four children to enjoy. Jupiter Artland is open at weekends, during the summer, for a modest entrance price of £5.

“I dislike private collections that are not open to the public,” says Robert Wilson as he surveys Stone Coppice — boulders inserted into coppiced sycamore trees by Andy Goldsworthy. It is an amazing spectacle, 54 hefty lumps of basalt, weighing up to 14 tons, sitting inside the trees as if dropped there by a careless giant. He wants everyone to marvel at it as he does. “Otherwise it’s like King Midas, sitting on his own, counting his money.”

Nobody could accuse Wilson of that. His family owns Nelson’s, the homeopathic medicine firm behind Rescue Remedy. As company chairman, he commutes to London for part of every week. Starting a sculpture park was not at the top of his to-do list. It was his wife, who studied at Camberwell and Chelsea art colleges, who found Bonnington House, relocated the family, looked up Jencks in the phone book and persuaded him to build Life Mounds, his largest piece to date, on their land.

Life Mounds was initially to be half its size. Wilson “begged and persuaded” the neighbouring farmer to sell him a field so Jencks could have the space his vision required. “Did he think we were bonkers? Of course, absolutely. But he came to the opening and seemed very impressed.”

The Jencks piece took “five bloody years” from the first digger full of earth to the final cut on the immaculate grass. Once that was under way, Jupiter Artland grew arms and legs. Wilson now considers it “his life’s work”.“We wanted to find sculptors we really like, whose work we admire,” he says. “We wanted to start at the very top, to create signature pieces that would give the park status.”

The Wilsons can consider that job done: Goldsworthy, Quinn, Gormley and Jencks have been joined by Anish Kapoor, a Turner prize winner. “From there,” says Wilson, “we broadened it out to artists who may not be yet in the premier league, but whose work is interesting". Into that category leaps Peter Liversidge — “tomorrow’s big man”, according to Wilson. There is one permanent piece of his work in the park, a signpost pointing to the planet Jupiter. Liversidge has ideas for 133 more, however. He sent the Wilsons 134 proposals for artworks, including the event that happened last week. On midsummer’s day, he turned a tiny segment of the forest into a winter wonderland with a temporary snowstorm.

If that sounds nuts, consider some of his other suggestions. (They are framed on the wall of one of the converted-barn galleries, to be read and enjoyed with coffee and cake). He would like to invite Iggy Pop, Gary Numan, the Red Arrows and the University of Montana’s Grizzly Marching Band to perform in the park. (Separately, thankfully). A helter-skelter, a monorail, a stairway to a door that never opens and an underground bunker are just a few of the building projects he has in mind. The staff should, he reckons, dress as wolves for one day every year. Or perhaps wear the uniforms of Japan Airlines.

Liversidge is a huge supporter of the Wilsons’ vision. “This is philanthropy on a grand scale,” he says. “It’s of another era. The decisions are with you, the artist. You are given free reign.”

The Wilsons would like to do one of his proposals every year. The staff are already lobbying for their wolf costumes.

It is all part of the plan to allow Jupiter Artland to grow manageably. When it closes in the autumn, new artists will arrive to work on pieces commissioned by the Wilsons over the summer. Nathan Coley, a Scottish artist shortlisted for the Turner prize in 2007, is already planning a graveyard in a quiet, overgrown spot. Jim Lambie, a Glaswegian who tends to pile up chairs and cover floors in stripes, has agreed to do something.

By footing the bills themselves — and the Wilsons will not say how much they have spent — they have created the sculpture park they want, free from the constraints of committees and councillors. “We do not expect, and have not looked for, grant aiding,” he says. “The Arts Council expect you to jump through all kinds of hoops and make all kinds of presentations, and then they might give you £25,000.”

The Wilsons keep down costs by commissioning work directly. “It is not as if we are paying gallery prices and commission.” (Suck, part of the Kapoor piece, is the only one they have bought from a gallery).

As they develop a relationship with the artist, the price often comes down. But the incidentals must be terrifying. A hundred tons of soil had to be moved to create the setting for Gormley’s Firmament. Despite the efforts of two full-time gardeners, Life Mounds still has a bare side that has yet to be seeded with grass.

It is, says Wilson, all worth it. “It gives the woods a reason for being. It becomes so much more than a pretty landscape.”

www.jupiterartland.org

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