A garden at the Baltimore residence of Leo and Pauline Vollmer was among those designed by the D.C. firm Oehme, van Sweden and Associates. (Roger Foley/Courtesy of the Cultural Landscape Foundation)

Washington doesn’t export a lot of aesthetic ideas, and the exceptions only prove the rule. Yes, the city can lay claim to the Washington Color School, more than a half-century ago, but that always feels a bit like the region’s claim to culinary fame, the crab cake: predictable, ubiquitous and uninspiring. But what has become known as the “New American Garden” did indeed take root in Washington before going viral, and its larger impact is so pervasive that it almost goes unnoticed.

The National Building Museum has devoted an exhibition to the local design firm founded by Wolfgang Oehme and James van Sweden, which popularized the New American Garden, a loose but luxurious style of landscape design, full of layers and texture, and an abstract sense of color, shape and topography. Beginning mainly with private clients in the 1970s — and eventually taking commissions from major public gardens, federal buildings and commercial entities — the firm became one of the busiest and most influential in the country. Van Sweden died in 2013 and Oehme in 2011, but the office continues under its new name: Oehme, van Sweden OvS.

The exhibition underscores the local roots of the company with a painting borrowed from the National Gallery of Art: Pieter de Hooch’s “A Dutch Courtyard,” from 1658-60. Also included is a large-scale reproduction of Helen Frankenthaler’s 1973 “Nature Abhors a Vacuum,” also in the National Gallery.

These are two very different works of art, separated by centuries and a revolution in visual culture. The de Hooch is a serene, formally structured image of people relaxing in a courtyard of wood and brick. The Frankenthaler is a watery abstraction of earth tones and secondary colors, suggesting a deep vista into a wide-open landscape. Yet taken together they reveal several of the productive tensions in the work of Oehme and van Sweden, between enclosure and openness, artifice and informality, the hard line and the permeable interface.

The de Hooch courtyard recalls a typical Oehme and van Sweden feature, outdoor “rooms” defined by tall plantings that create intimate bounded spaces; and an open door in the painting, with a hint of trees behind it, alludes to the sense of “mystery” and narrative unfolding that the designers hoped would draw people through their gardens. These defined spaces, often deployed near a house, eventually give way to more open areas and more fluid plantings — a more “Frankenthaler sense” of space — that yield views to natural features that define the property.

Even in gardens that are relatively small, undulating layers of plants at subtly different heights create the illusion of a larger space, as if an extensive landscape has been gathered and compressed into a small frame. For centuries before Oehme and van Sweden, gardens were designed to become more “wild” as they flowed out from a central architectural feature; the difference in the New American Garden is that the sense of the wild wasn’t always forest but often a prairie, a seemingly endless expanse of flowing grasses.

The exhibition has been organized in part to mark the 25th anniversary of a book the two designers authored with Susan Rademacher, “Bold Romantic Gardens.” The word “romantic” is apt, even if the exhibition curators argue “their style evolved from the modernist tradition.” Almost every project they touched could go both ways, as much E.M. Forster (heavy curtains of green coddling resilient enclaves of civilization) as James Joyce (unbridled torrents of seemingly formless visual stimulation). But all of it is highly structured, contrived and almost dogmatically artless.

Nature has never looked so perfectly WASPish in its mix of buttoned-down calculation and meticulous imperfection, the pattern of the necktie (just so slightly open) clashing (ever so pleasingly) with the shirt, jacket and aggressively bright pants. While the firm did pro bono projects (including the German American Friendship Garden on the Mall), the exhibition tracks its committed service to the super wealthy: Kendale Farm, a 2,500-acre estate in Virginia with five miles of Rappahannock River frontage; an 85-acre Nantucket, Mass., coastal estate; a 25-acre property with a 19th-century farmhouse in Greenwich, Conn.; an 11-acre compound on Kiawah Island in South Carolina. The list goes on, and on, and on.

Washington may have been the perfect breeding ground for the style. One of the team’s seminal projects, and its first public demonstration of the principles behind the New American Garden, was designed for the grounds of the Federal Reserve Board, with two buildings, one on Constitution Avenue and another across C Street NW.

The Paul Cret-designed main building is a classic example of the stripped-down, elegant but dour classicism that defines so many government properties built in the 1930s and ’40s in Washington. The innate conservatism of this federal architecture, its austerity and expressive reserve, calls out for subversion and tweaking, which Oehme and van Sweden supplied with their unruly sweeps of ornamental grasses. With its forests, marshlands, tidal zones and flat, wide rivers, the region around the nation’s capital is also wonderfully diverse in ways that clearly appealed to the artists. The climate also welcomed invasive species they used in abundance, including ornamental Miscanthus grasses.

When the two designers formed their firm in 1975, they were in argument with the dominant thinking of the day, which was all about flat planes of grass and formal edges. But fashions come and go, and while the flat plane of grass cloys in its reflexive suburban deployment, it looks spectacular when you plunk an Alexander Calder or Mark di Suvero sculpture on top of it. Today, the work of Oehme and van Sweden feels like the classic overstuffed leather chair: luxurious, genteel and slightly old-fashioned.

Changes in fashion, however, aren’t to be taken lightly when it comes to landscape, which is particularly susceptible to destruction and forgetting. According to exhibition co-curator Charles Birnbaum, head of the Cultural Landscape Foundation, nine of the 21 projects first presented in “Bold Romantic Gardens” have been destroyed. And several of the projects in this exhibition, including one created for John and Evelyn Nef in the District and a garden van Sweden designed for his vacation home on the bay in Maryland, have been lost or altered beyond recognition. The firm’s 1988 redesign of the Pershing Park grounds on Pennsylvania Avenue is in imminent danger of loss if plans for a major redesign of that space — expanding it to memorialize the First World War — go through.

The garden as high-end accouterment for the 1 percent will always be vulnerable, especially to that particular breed of the super wealthy whose self-esteem is tied up with the exercise of power over the land, people and things. Such people will always want to make and remake and fashion the world again to reflect their status and taste.

But this exhibition makes a strong case that there are also public masterpieces among the works designed by van Sweden — the Federal Reserve grounds and an island and water basin the firm created for the Chicago Botanic Garden — the loss of which would be grievous. Although it doesn’t include much sense of the background against which the designers were working — the status quo they challenged — it gives a thorough sense of their accomplishment, their style and their influence. It is also the largest monographic exhibition the National Building Museum has devoted to landscape architecture, and it bodes well for yet more attention to this often-neglected discipline.

The New American Garden is on view through May 1 at the National Building Museum, 401 F St. NW.
202-272-2448. www.nbm.org.