"The idea," says the 64-year-old Dutchman known as the father of the influential New Perennial movement, "is not to copy nature, but to give a feeling of nature." In Piet Oudolf's gardens -- from private landscapes in Europe to public parks in Chicago and New York -- towering grasses catch the breeze and masses of flowering plants provide flashes of color. Including brown: "Dying in an interesting way is just as important as living." Oudolf's latest project is planting the High Line, a long-abandoned 1.5-mile elevated railway in Manhattan. "It will tell a story as you walk along, from a woodland idea into meadow, from monocultures into more complex layering," he says. "You can analyze it if you want. But really, what you see is what it is." -- by Denise B. Martin