Weiss/Manfredi and Reed Hilderbrand's redesign of Longwood Gardens is reaching full bloom

As a passionate admirer (and engineer) of water in the landscape, the late American industrialist Pierre S. du Pont would be thrilled to return today to Longwood Gardens, his country estate-turned-garden wonderland in the Brandywine Valley of southeastern Pennsylvania.

Now rising atop a ridge in the 1,100-acre public garden, a state-of-the-art greenhouse appears to float above a shallow, 175,000-gallon pool. This ethereal marriage of water and steel-supported glass architecture continues in the newly opened West Conservatory, home to Longwood's expanded Mediterranean Garden. Here, guests can traverse a lush landscape of low-rise fountains, canals, pools, planted islands and other water features totaling more than 8,000 square feet.

Crowned by a pleated roof with crisp asymmetrical peaks that define Longwood's new “crystalline ridge,” the 32,000-square-foot West Conservatory is the centerpiece of a $250 million revitalization project.

Led by New York-based Weiss/Manfredi in the role of lead designer and master planner in collaboration with landscape architecture firm Reed Hilderbrand, the project encompasses 17 acres of the century-old garden's central conservatory area. Several key elements completed as part of the renovation opened adjacent to the West Conservatory in late November. Led by Paul Redman, President and CEO of Longwood Gardens, these efforts include the careful relocation of Brazilian landscape architect Roberto Burle Marx's Cascade Garden (1993), his only completed work in North America, from a retrofitted space within the main conservatory a new custom greenhouse; the construction of the Grove, an airy administrative and educational building with classrooms, staff offices and a 20,000-volume library; the creation of an outdoor bonsai gallery and adjacent workshop in a historic, renovated potting shed; and the debut of a fine-dining restaurant and event venue built beneath Longwood's historic 1921 Winter Garden, where a retaining wall once stood. This hidden room looks directly south over the waters of Longwood piece of resistancethe main fountain garden, conceived and designed by du Pont himself.

Dancing to the delight of the public since 1931, the Main Fountain Garden, framed by box hedges and its 1,719 jets, has long been a (seasonal) attraction in Longwood, lending a distinct theatricality to the stately European-style gardens that surround it. Simply put, it's a spectacle. The vibrant and impressive Main Fountain Garden, which underwent a $90 million infrastructure upgrade in 2017, is a fitting counterpart to the tranquil pools of Weiss/Manfredi's West Conservatory. While both are fascinating, Longwood's new “floating” greenhouse, seamlessly integrated into the existing conservatory complex, has an immersive quality that underscores the garden's role as a place of discovery where a visitor's experience varies depending on their destination Way can unfold entry or time of day. “At best, a walk through a garden is always cinematic and not static,” says Marion Weiss.

Like the Main Fountain Garden, the West Conservatory is an engineering masterpiece, supporting beauty through (expertly hidden) engineering power. The 1,958-panel glass structure, which Weiss calls a “living, breathing building,” utilizes an advanced passive ventilation system in which 10,300 feet of earthen channels heat or cool air flowing into the main level of the conservatory and the pedestrian walkways. The air-tempering earthen ducts buried beneath the garden's southern slope reduce the building's reliance on mechanical cooling and supplemental heating while providing thermal comfort for guests. More than 400 roof vents and vertical windows now open and close in response to external climate fluctuations. A weather station installed on the roof of the nearby Grove building transmits information in real time to a computerized “activation brain trust” that controls the conservatory's operable elements, which include automatic blinds. In addition, a multi-stage geothermal heat exchange system connected to 127 geothermal wells provides heating and cooling to several buildings.

The robust sustainability strategies of course also extend to water. West Conservatory's pools are fed by biologically treated rainwater collected in channels along the building's folded roofline and stored in underground storage tanks. The water is also used for irrigation.

Water was an early key element of Reed Hilderbrand's design for the Winter Garden's Mediterranean garden, which features 60 different species representing six global ecozones. “The pools were an opportunity to highlight the topography of the garden rather than building it,” explains director Kristin Frederickson, pointing to the way the Mediterranean has carved cliffs, caves and other coastal landforms over the millennia. “There's a way in which this very simple body of water allows the building above it to express itself – and then the expression of the pools inside is about the interweaving and the way it creates islands, thresholds and bridges emerge,” she adds.

There's much to admire about the revitalized Longwood: the groundbreaking blend of reconstruction and preservation behind the “new” (and now ADA-compliant) Cascade Garden, which will serve as a template for similar future efforts; quieter, unifying moments such as the Central Grove and its avenue of gingko trees, which provide access to the Cascade Garden, the Bonsai Courtyard and the existing Waterlily Court, framed by a new arcade; and Longwood's partnership with the Challenge Program, a Delaware-based nonprofit that provides job training to at-risk youth. The program produced nearly 50 pieces of furniture from wood harvested from trees on the site that were felled by storms. Many of these furnishings can be found in the new restaurant, which is named “1906” in reference to the year du Pont purchased a heavily forested piece of farmland, now home to Longwood Gardens, to protect it from logging preserve.

But it's the pool-surrounded West Conservatory that lays the foundation for this herculean redesign. As with du Pont's fountains, this elegant 21st-century version of the Victorian greenhouse artfully blends water and landscape to transport visitors from Chester County, Pennsylvania to a very different place.