IT’S BEEN CALLED the single-most-ambitious new garden at the Washington Park Arboretum since the Depression-era WPA projects. A decade in the planning, and more than a year in construction and planting, the New Zealand Forest debuts next weekend.

It’ll be years before the garden will grow into anything resembling a forest. But the vast scale of the project, and the scattering of semi-mature silver beech trees (Nothofagus menziesii) give an idea of how dramatic the garden will be as it fills in and grows up. “This will be an experience like no other . . . Now there’s no need to get on a plane to New Zealand,” says horticultural manager David Zuckerman.

If flowery Azalea Way comes to mind when you picture the Arboretum, prepare yourself for a surprise, if not a shock. The first of the Pacific Connections gardens to be fully planted, the New Zealand Forest is a 2½-acre hillside featuring nearly 10,000 odd, twiggy, twisted plants from Down Under. “We call it the ‘New Zealand dead look,’ ” says Zuckerman of the contorted corokia and brown-toned carexes. “Trust us, all these plants are alive.”

Zuckerman toured me around the site on a summer day when workers swarmed the slope, planting hundreds of little shrubs and grasses. Landscape architect Andy Mitton of the Berger Partnership, designers of the garden, was scrambling around placing plants. Crews from the Seattle Parks Department and W.S. Contractors worked side-by-side. The Arboretum Foundation helped raise the money, and the University of Washington Botanic Gardens spearheaded and shepherded the project along.

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The huge boulders that frame the entry to the garden were arranged to echo the feel of New Zealand’s Arthur’s Pass. From this high point, you can see over the restored stone lookout, an Arboretum landmark since the 1930s, to a skyline of the University District. Rock drainage swales tumble down the slope, creating a framework for the plantings. A wide path gently switchbacks through seven overlapping vegetation zones. From beech forests to shrub lands and grasslands, each area represents actual plant communities found in the mid-to-high elevations on the South Island of New Zealand.

“The plantings are unlike anything seen in the Northwest before,” says Ray Larson, curator of Living Collections.

The garden is rich with take-home ideas, especially for those with sunny gardens and well-draining soil. Some of the plants, like hebes, phormium and pampas grass, will look familiar. But most are distinctly exotic, many with wiry black stems and foliage in tones of blue or silver.

“We’re creating a forest from a different area of the world that we know will grow well here,” explains Zuckerman, who emphasizes the conservation aspects of the garden. Like a zoo, the Arboretum is protecting the germ plasm of the future. “We’re keeping genetic diversity alive here,” he says.

Valerie Easton is a Seattle freelance writer. Check out her blog at www.valeaston.com. Mike Siegel is a Seattle Times staff photographer.