Longwood Gardens, famous for its plants and classical fountains, adds modern architecture to the mix

For Longwood Gardens, horticulture has always been an opportunity for spectacle. Sure, visitors can stroll its classically manicured paths, admire its extraordinary collections of water lilies and orchids, and take classes on the fine points of composting. But the former du Pont estate in Chester County is equally famous for its dancing fountains, over-the-top Christmas displays, and weird plants that bloom at night and emit rancid smells.

That theatrical sensibility is on full display in a group of new buildings that will open in November, the culmination of a decade-long effort to modernize the popular public garden. As part of the $250 million project, called “Longwood Reimagined,” the garden’s core attractions were expanded, parking lots and greenhouses were relocated, and a new restaurant was embedded in the foundations of the original conservatory. These changes have dramatically improved the views from Longwood’s famous fountain garden. But that’s not all that’s been accomplished.

Longwood, which is largely known for its plant specimens and classical fountains, can now also boast about its modern architecture.

While each of the new buildings is superb, Weiss/Manfredi’s eye-catching conservatory for Mediterranean plants clearly steals the show. Viewed from the fountain area, the structure appears to rise up like a crystal mountain range, its roof rippled with an asymmetrical series of peaks and valleys. Those origami-like folds are outlined by a sharp-edged, white steel frame that gives the entire design the crisp snap of a bracing fall day.

The new structure is Longwood’s second large conservatory, and it bookends the stately stone-and-glass complex that Pierre du Pont began developing in the 1920s. The decision to place Weiss/Manfredi’s glass house — now called the West Conservatory — at the end of this row of garden buildings is really the key to the success of the project. Together with new walking paths and plantings by the landscape firm Reed Hilderbrand, the revised sequence turns what had been an awkward jumble into a cohesive ensemble.

Although Weiss/Manfredi is an architecture firm, it is well known for its garden work. Its principals, the husband-and-wife team of Marion Weiss and Michael Manfredi, have made their reputation designing buildings that blur the distinction between architecture and landscape. Projects like the Olympic Sculpture Park in Seattle, the visitor center at the Brooklyn Botanical Garden, and, to a lesser extent, the nanotechnology building at the University of Pennsylvania are all meant to look like extensions of the natural topography.

So it’s ironic that their design for this garden project is really more building than landscape. By that, I mean the structure rests on top of the earth, instead of burrowing into it. The conservatory appears to levitate above Reed Hilderbrand’s elegant reflecting pool, further emphasizing its verticality.

The West Conservatory’s white steel structure doesn’t just provide support for the design; it really is the design. The columns emerge from the ground like tree trunks, before branching off to support the roof. For many, the arching forms will evoke the rib vaults in Europe’s gothic churches. Yet the tree motif also takes us back to the earliest days of architecture, when humans first began stringing tarps between branches to create shelter.

In many ways, the two glass houses offer a compressed history of conservatory design. Pierre du Pont began to create what became Longwood Gardens in the 1920s, after visiting Joseph Paxton’s celebrated Crystal Palace, the 19th-century London building that started the Victorian fad for glass exhibition halls. He later attended several important American world’s fairs, including those in Philadelphia and Chicago, and spent time studying Italy’s neoclassical garden structures.

It would be too much to say that Weiss/Manfredi have reinvented the 19th-century conservatory form that inspired du Pont, but they have certainly given it a beguiling modern twist. Their white steel acts as a counterpoint to the dark metal frame used to outline the roof of du Pont’s conservatory. Without the clutter of rooms, walls, or ornamentation, the more minimalist West Conservatory feels like pure architecture.

Like many public gardens, Longwood has increasingly adopted sustainable practices. Weiss/Manfredi have furthered that effort by embedding the structure with the latest green technology, including an underground geothermal system that passively heats and cools the building, wood details carved from fallen trees found on Longwood’s property, and bird-safe glass. When the interior becomes too hot, Longwood’s gardeners can simply open the windows, which Weiss says act “like the gills of a fish.”

Reed Hilderbrand’s interiors also bring a fresh perspective to Longwood. To complement the lush displays in the East Conservatory, the new building features a drier Mediterranean landscape. The plantings include century-old olive trees, citrus trees, and thyme and rosemary plants, all in shades of silver and sage. The shallow pools inside the conservatory were designed to give the water a pale cast. The whole space manages to capture the gauzy quality of Mediterranean light.

The decision to reorganize the buildings on the ridge overlooking the fountains was first proposed in a 2011 master plan prepared by Weiss/Manfredi. To give the ensemble more cohesion, they recommended shifting the location of Roberto Burle Marx’s celebrated Cascade Garden from the edge of the ridge to the midpoint between the two conservatories. But that meant they would be taking chances with one of the masterpieces of 20th-century garden design.

Burle Marx, a hugely influential Brazilian landscape architect, had been commissioned by Longwood Gardens in 1989 to create a tropical garden. He produced a gorgeous painterly composition that evoked the Brazilian rain forest, complete with rock formations and cascading waterfalls.

His garden was installed inside a small glass house. At the time, Burle Marx’s Philadelphia collaborator, Conrad Hamerman, likened the arrangement to “building a ship inside a bottle.” He probably sensed that the enclosure was going to be too small for Burle Marx’s ambitious design, and it wasn’t long before the plants began pushing against the roof.

Since the garden is the only surviving Burle Marx project in North America, Longwood was determined to preserve it with as few changes as possible, said Paul Redman, the garden’s president and CEO. While preservation architects move historic buildings all the time, no one has ever attempted to relocate a historic garden before, according to Redman.

To preserve the integrity of Burle Marx’s design, Longwood gardeners had to catalog and number every plant and stone so they could be transferred later to the new enclosure. During construction, the stones were put in storage, and Burle Marx’s plants, which include several varieties of bromeliads, were kept alive in greenhouses.

Gardeners were still piecing the garden back together when I visited. But, based on what I saw, Burle Marx’s garden should look as good or better than before. The new glass enclosure by Weiss/Manfredi is more understated than their West Conservatory, just a simple glass box with a peaked hat, framed with dark steel. But Reed Hilderbrand was able to create a small, welcoming forecourt with a curved path that winds into the building and through the miniature rain forest. That walkway design is the only deviation from Burle Marx’s original. Unlike the 1989 path, it will be handicap accessible.

One of the advantages of placing the Cascade Garden between the two conservatories is that visitors can now approach the tropical garden from either end of the complex. To help them find their way, the architects created a covered arcade, bordered by an allee of ginkgo trees.

The pathways lead to a new outdoor bonsai garden designed by Reed Hilderbrand principals Kristin Frederickson and Eric Kramer. Longwood decided to create the small display area after America’s foremost bonsai collector, Doug Paul, donated a portion of his collection to the garden. The serene space, which is tucked away behind the West Conservatory, should give visitors a place to unwind at the end of their visit. Wood benches, crafted from fallen trees, line the courtyard and offer spectacular views of the Brandywine Valley countryside.

From there, visitors can descend into the fountain garden. For years, Longwood covered up a blank wall with a trellis of magnolia trees. When Weiss/Manfredi discovered there was just earth behind the wall, they decided to excavate and install a large, sit-down restaurant overlooking the foundations.

Instead of continuing the minimalist language of the West Conservatory, they deferred to du Pont’s classical architecture and designed a series of large arched windows. Although the new space is long and narrow, the windows bring in ample light and will allow diners to enjoy the choreographed fountain display. Eventually, the magnolias, which produce white flowers, will grow back, outlining the windows in green.

Even before undertaking these additions, Longwood Gardens was already the most popular paid cultural destination in the Philadelphia region. More than 1.6 million visitors a year come to admire the plants and elaborate fountain displays. Those attractions will always big the big draw, but now they have to share the stage with Longwood’s stunning new buildings.