Spanning some 40 hectares, Pennsylvania’s Longwood Gardens is one of North America’s most storied horticultural settings. It’s a heritage that spans thousands of years, reflected in the wealth of Lenape artifacts discovered across the site — an immemorial hub of agriculture, fishing and hunting. In the late 18th century, an impressively diverse arboretum stretched across the landscape, becoming a popular outdoor gathering spot for community picnics and socials. And just as the site faced a turn-of-the-century decline, its 1906 purchase by business magnate Pierre Samuel du Pont spurred the creation of the public garden still renowned across the world today.
The story doesn’t stop there. After Longwood Gardens officially opened to the public in 1921, the outdoor gardens and greenhouse conservatories — the first of which was merely an expanded farmhouse — were continually expanded, comprising 13 indoor gardens (and hundreds of species) alongside a richly varied landscape of open air environments a century later. Along the way, luminaries ranging from Thomas Church, Peter Shepheard and Roberto Burle Marx to Dutch landscape architects West 8, have left their mark on an evolving, living canvas. The latest? Weiss/Manfredi and Reed Hildebrand.
In a site full of iconic settings, the New York-based architects and Massachusetts landscape architects have contributed one of Longwood’s most ambitious environments. Undertaken as part of a larger 6.8-hectare renovation of the non-profit complex, Weiss/Manfredi and Reed Hildebrand have unveiled a striking new greenhouse — the West Conservatory — spanning nearly 3,000-square-metres. Situated on a prominent hillside setting alongside the main conservatory building, the facility replaces a cluster of older greenhouses and service buildings that previously occupied the site.
Home to an expansive Mediterranean garden, the West Conservatory is both an ecological and architectural showpiece. Inspired by the site’s rolling landscape and its wealth of arboreal beauty, Weiss/Manfredi’s varying and slightly irregular array of steel columns bends and weaves across the roof like the myriad branches of a tree canopy. It’s a delightful departure from convention, yet one that recognizably riffs on the greenhouse typology, while also picking up on the roof lines and geometries of older neighbouring buildings.
Inside, Reed Hildebrand’s Mediterranean landscape evokes a series of canals, all traversed by paths and walkways, and animated by aquatic plants and water lilies. Like the structural envelope that houses it, the garden presents a reconsideration of a typical greenhouse program. In lieu of a conventional central pool, water and earth are interspersed throughout, making for a more dynamic journey through the garden. “We approached this project with a commitment to creating immersive gardens that both celebrate the richness of Longwood’s existing collections and expand them for the next century,” says Reed Hildebrand principal Kristin Frederickson.
The playful yet well-considered aesthetic is amplified with sustainable design strategies. Under the greenhouse, 128 geothermal wells are connected to a ground-source, multi-stage heat exchanger, which provides heating and cooling to the new conservatory, as well as the neighbouring facilities like the administration building. 10 broad earth ducts also moderate indoor temperature, creating more comfortable conditions for people and plants alike. But the most ingenious innovation may be the simplest one: 424 adjustable louvered windows that allow the greenhouse to maintain ambient temperature through most of the year, requiring mechanical heating when fully closed in the winter.
While the West Conservatory forms the showpiece of the 6.8-hectare renovation project, it’s not the only new presence at Longwood Gardens. Weiss/Manfredi also oversaw the meticulous relocation of Roberto Burle Marx’s Cascade Garden into a custom-designed new greenhouse. Completed in 1993, the project is Burle Marx’s only existing landscape in North America.
The ageing and cramped building that housed the garden has been replaced with a new structure that maintains the exact specifications of sunlight and topography specified by Burle Marx. Moreover, the architects designed an elegant administration building for Longwood Gardens, as well a new home for the site’s long-established 1906 restaurant, which was carved out from a space behind the Main Conservatory’s retaining wall. It is all a testament to contextual sensitivity.
For Weiss/Manfredi co-founders Marion Weiss and Michael Manfredi, the innovative architectural expression is in service to the enduring spirit of place. “With the West Conservatory as the centrepiece of this newly conceived crystalline ridge, the pleated roof, branching columns, and tapered perspectives extend the marriage of architecture and horticulture that is intrinsic to Longwood’s identity,” say the architects.
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