Wolfgang Oehme, a German-born landscape architect whose radical ideas changed the face of the American garden, died Dec. 15 in Towson, Md. He was 81.

The cause of death was metastatic colon cancer, said Carol Oppenheimer, his colleague and, later, his caretaker.

With the landscape architect James van Sweden, Mr. Oehme (pronounced UR-ma) forged an unlikely partnership that became the Washington-based firm Oehme, van Sweden & Associates. The alliance began in earnest obscurity in the 1970s: They planted their own designs from the back of a pair of Volkswagen Squarebacks.

When a Federal Reserve Board member asked them to redesign the Fed’s Virginia Avenue NW gardens in the 1970s, the resulting two-acre confection of fountain grass, Autumn Joy sedum and feather reed grass showed the world an alternative to the old city park model of foundation evergreens bordered by ivy ground cover.

A slew of public and private commissions followed, other designers aped the style and nurseries had to grow and sell the Oehme-van Sweden plant palette to keep up with demand.

In addition to various grasses, the team popularized such perennials as black-eyed Susans, coneflowers, joe-pye weed, salvias and Russian sage.

With artful promotion, they called their style “the New American Garden” and said their gardens served as a metaphor for the American prairie.

In addition to designing gardens for adventurous and well-heeled clients, the firm also shaped prominent public spaces in the Washington area, including Reagan National Airport, the National World War II Memorial and Freedom Plaza.

Their champion at the Federal Reserve, David Lilly, wrote that the garden there evoked imagery that moved “away from the aristocratic European model” toward a more egalitarian “Great Plains heritage.”

The gardens were also rooted in Mr. Oehme’s Germanic passion for improved varieties of grasses and perennials planted as they might look in nature — carefully grouped and en masse. Mr. Oehme loved that his gardens attracted birds, bees, butterflies, dragonflies and frogs, but his plants were not native to one land or region. Mr. Oehme was looking for effect, not ecology.

A major influence was Karl Foerster, a plant breeder and writer active before World War II who emphasized the natural and dynamic seasonal aspects of herbaceous gardening.

Throughout his life, Mr. Oehme returned to a saying of Foerster’s: that grasses “were the hair of the Earth.”

Wolfgang Walter Oehme was born in Chemnitz, Germany, on May 18, 1930. He began growing plants when he was 5, in a corner of his parents’ community garden plot.

He moved north with his family to Bitterfeld in 1943 when his father was transferred to the city as a policeman during World War II. The city later became part of East Germany under Soviet control.

Mr. Oehme apprenticed at 17 at a Bitterfeld nursery, where he learned plants, propagation and planting techniques. He later moved to the city parks department, where a mentor introduced him to the ideas of Foerster and encouraged him to become a landscape designer.

Mr. Oehme graduated from the University of Berlin in 1954 with a degree in landscape architecture. Three years later, with his homeland increasingly divided by the Cold War, he packed a bag and came to Baltimore to work for landscape architect Bruce Baetjer.

Mr. Oehme took a job with the Baltimore County Recreation and Parks Department but was soon doing private gardens on the side for brave clients who would replace their suburban gardens of lawns and azaleas with strange grasses and long flowering perennials.

The sight of the standard passive yard, enlivened by pansies in spring and impatiens in summer, made Mr. Oehme cringe. “When I came to Baltimore, it was like a desert,” he wrote. “I went on a crusade.”

Clients discovered that they had to clothe and feed the eccentric young emigre, said Kurt Bluemel, another German plantsman who made a name for himself in Maryland in the 1960s. Mr. Oehme was a Romantic who fed his imagination with the poetry of Goethe.

One of Mr. Oehme’s important early gardens was done for Leo and Pauline Vollmer in the Baltimore suburb of Murray Hill. In 1964, van Sweden, then an urban planner in Washington, heard about it and took a look. “I had never seen such a beautiful garden in my life,” he wrote. “I knew right then that Wolfgang Oehme was somebody to grapple with, to be involved with.”

In 1971, they together designed and installed the garden of van Sweden’s rowhouse on N Street NW in Georgetown, which they used as a horticultural showroom to attract clients. They founded their firm in 1975.

Van Sweden, now retired, wrote or co-wrote four books about their partnership and design philosophies. He was a polished speaker. Mr. Oehme, by contrast, spoke laconically and with a thick German accent and was more at home with a shovel than a microphone.

Mr. Oehme’s marriage to the former Shirley Zinkhan ended in divorce. Survivors include a son, Roland Oehme, a landscape architect in Towson; and a grandson.

Mr. Oehme left the company he started, officially retiring in 2008, and the same year established a small firm with Oppenheimer called Woco Organic Gardens.

Mr. Oehme once had a large house and a dazzling, multi-terraced garden in Towson, but he ended his days in reduced circumstances, in a small apartment not far away.

In October, he paid his final visit to Germany, where he reviewed a project he took on late in life that served to close the circle of his career. Alongside a lake at the Goitzsche Park in Bitterfeld, he helped to regenerate a brownfield site with broad sweeps of rudbeckias, euphorbias, switch grasses and the like.

From his bed two days before his death, Mr. Oehme surveyed framed photographs of the park as well as his German forebears. He pointed to the various plants in their autumn flower and color. “Thousands and thousands,” he said, weakly, mustering a smile.