THE SONOMA VALLEY , best known for its rolling hills, boutique wineries, and Mediterranean-style villas, is not the kind of place one would expect to find a rotting Monterey pine festooned with 80,000 sky blue plastic Christmas baubles, or a giant haystack that broadcasts a looped crackly recording of Johnny Cash's "Ring of Fire." But since it opened its gates last July on a nine-acre tract of land off Highway 121, the Cornerstone Festival of Gardens has rocked the otherwise genteel sector of oenophilia with a riot of botanical bombast.

Devoted to exhibiting some of the edgiest expressions in gardening by leading international landscape designers, Cornerstone is the first outdoor gallery of its kind in the United States. The gardens' founder, Chris Hougie – an ex-toy company owner who made his fortune with those glow-in-the-dark astronomical stickers one finds on bedroom ceilings – initially found inspiration for the project in 1996 while honeymooning in France, where he visited the International Garden Festival at Chaumont-sur-Loire.

Taken by the idea of creating a series of evolving walk-through gardens, Hougie collaborated with Peter Walker, an acclaimed conceptual architect whose credits include the World Trade Center Memorial in New York. They invited 15 landscape luminaries, including Martha Schwartz, Claude Cormier, Yoji Sasaki, and Christophe Girot, to create inaugural exhibits (average size: 1,800 square feet) that would exemplify the connection between art, architecture, and nature.

Cornerstone is probably not your Aunt May's idea of a garden. Visitors looking for something out of a Merchant-Ivory film, like neatly planted rows of pansies and sweet williams, dotted with burbling fountains and ornamental cherubs, or Monet's water lilies, will be disappointed. Cornerstone's mandate encourages another kind of endeavor altogether. Extreme statements of artifice such as American designer Ken Smith's Daisy Border, a display of candy-colored plastic pinwheels, both mock and pay homage to the classic floral border. Mexican architect Mario Schjetnan's A Small Tribute to Immigrant Workers' regimented boxes of vegetables and rude red plywood and rusty metal walls deliver a strong message about the plight of immigrant workers in California.

Unlike many a pristine country garden, Cornerstone is open to the public year-round. Some exhibits, like Schwartz's comical mini golf-inspired landscape The Usual Suspects, are "evergreens," maintaining their appearance regardless of the season. But others are subject to the forces of time and climate, as I learned on the cold, dank late-December morning I selected for my visit.

While appreciating Cornerstone's respect for (and celebration of) the cycle of organic life, I regretted not being able to witness the full bloom of gardens like Paris-born Girot's The Pod, currently closed to visitors as it matures, and Vietnamese designer Andy Cao's [Ninnananna] A Lullaby Garden, hidden under a black plastic tarpaulin. Literature for the latter exhibit enticingly described it as being made from 200 hand-knitted nylon carpets, representing three months of labor by 60 Vietnamese villagers. "Leave your shoes; immerse yourself," a nearby plaque states. Nothing to do but plan another visit in spring.

That's not to say Cornerstone isn't worth visiting in the winter. The gardens provide an oasis for the senses on even the darkest day. Montreal-based landscape architect Cormier's visually arresting Blue Tree looks like a giant piece of blue coral against the sky. Tom Leander's Break Out, which invites visitors to wander around a maze of haystacks interlaced with creaky screen doors, makes for a sonic experience with music courtesy of "Man in Black" Cash. With its corridor of eucalyptus screens, Bay Area-based landscape architect Walter Hood's Eucalyptus Soliloquy smells as fresh as it looks. Other gardens, like Topher Delaney's Garden Play, inspire tactile appreciation: visitors feel the texture of broken oyster shells underfoot as they play with scattered metal pétanque balls against a backdrop of silver birch trees.

Cornerstone's other attractions include an indoor gallery, a garden center, a landscape art and design store, and – starting March 1 – the Market Café, which will serve breakfast, lunch, and beer and wine. A lecture series about the gardens is planned for the coming spring, and while there isn't a formal education program, each year the gallery hosts a student exhibit. A garden designed by students in UC Davis's landscape architecture program is currently on display, and installations from UC Berkeley and Harvard University are scheduled to follow in 2005 and 2006.

Trip planner

Cornerstone Festival of Gardens Mon., noon-4 p.m.; Tues.-Sun., 10 a.m.-5 p.m. 23570 Highway 121, Sonoma. $4-$9. (707) 933-3010, www.cornerstonegardens.com.

About an hour's drive from San Francisco, Cornerstone is conveniently close to some nice wineries. Viansa Winery and Italian Marketplace (www.viansa.com) is just down the road; the Gloria Ferrer Champagne Caves (www.gloriaferrer.com) are across the street.

If you're looking for an aerial view of Sonoma, check out the nearby Vintage Aircraft Company (www.vintageaircraft.com) for biplane and warbird rides.