HUMMELO, The Netherlands

ON a cold January afternoon in this tiny village near the German border, the garden designer Piet Oudolf put on a heavy coat and led the way out of the 1850s farmhouse he shares with his wife, Anja, and into his garden. After a few steps he stopped and pointed with pride at a stalk of dead fennel standing in a bed of moribund, wheat-colored joe-pye weed. “Normally, people who garden would have cut this back by now,” he said. “The skeletons of the plants are for me as important as the flowers.”

For Mr. Oudolf, in fact, the real test of a well-composed garden is not how nicely it blooms but how beautifully it decomposes. “It’s not about life or death,” he said, admiring the dark, twisting lines of the fennel. “It’s about looking good.”

Over three decades, Mr. Oudolf’s sometimes unconventional ideas about what looks good have helped make him a star in Europe  where his work has inspired an “ecology meets design” gardening movement called New Wave Planting by its followers  and have also begun to win him fans and jobs in the United States. He has done the planting design for important new gardens in Millennium Park in Chicago and the Battery in New York, and for the park that will cover the elevated High Line rail bed in Lower Manhattan when it opens in September. These landscapes, like all his projects, embody and advertise his fundamental aesthetic doctrine: that a plant’s structure and form are more important than its color.

“He’s gotten away from the soft pornography of the flower,” said Charles Waldheim, the director of the landscape architecture program at the University of Toronto. “He’s interested in the life cycle, how plant material ages over the course of the year,” and how it relates to the plants around it. Like a good marriage, his compositions must work well together as its members age.