Conservatories come in Crystal Palace and space frame forms, but they’ve never arrived quite like Weiss/Manfredi’s West Conservatory at Longwood Gardens. Located in Pennsylvania’s Brandywine Creek Valley, the 1,100-acre garden, once the estate of Pierre S. du Pont (heir and executive within that industrial empire), opened to the public in 1921 and has operated as a nonprofit since 1946. In the decades since, Longwood has enlisted a variety of top horticultural talents, from Thomas Church to Peter Shepheard and Roberto Burle Marx. Longwood boasts an edenic range of features, from an orangery to an Italian water garden to a 55-ton Aeolian organ, and it has now added possibly its most unique architectural feature.
The Gardens’ president and CEO, Paul B. Redman, had been acutely conscious that a prime spot next to the main conservatory was occupied by a “warren of old greenhouses,” largely fulfilling service functions, and led Longwood to find a better use for this space. An ensemble emerged through the joint efforts of Weiss/Manfredi and Reed Hilderbrand, centering on the new 32,000-foot Mediterranean-themed conservatory. In an interview with the two founders of Weiss/Manfredi, Marion Weiss and Michael Manfredi, the designers displayed one of their earliest sketches, drawing upon “the crisp lines of the existing conservatories and the wandering geography of the hills.” Their aim was to “take those two geometries and weave them together.” And that’s what they did at the West Conservatory.
The conservatory follows the existing axis, but Manfredi explained that they “looked to nature to find the most fantastic structural opportunities.” Post-and-beam lintels have been supplanted by trunk-and-branch here, for example: The conservatory is supported by arboreal steel columns that twist in irregular patterns beneath a roof composed of four varieties of undulating surfaces. “The columns never curve where you expect them to,” Manfredi said. “Some of these columns overreach and take on more of the span and others take less of it.”
That’s not all that’s striking. Conservatories often aren’t remotely sustainable—artificial climates usually haven’t been climate friendly. Some of the easiest “green” design strategies also won’t work with greenhouse structures: Glazing and laminate glass solutions choke plants off from the sun. A turning point for the West Conservatory design was the realization that Longwood didn’t require a year-round hotbox. To meet both sustainability and programmatic goals, Weiss/ Manfredi set out to make a structure that functioned more like “the gills of a fish.”
Mediterranean plants can live relatively happily in most mid-Atlantic temperatures (with some year-round adjustments for humidity, wind, and other factors). The only thing they flatly can’t survive is the northern winter. Weiss/ Manfredi took advantage of this climatic overlap to design a structure of remarkable permeability, with 424 louvered windows on the walls and roof. This allows the ambient outdoor temperature in for the spring, summer, and fall, but louvers can be closed to seal the conservatory upon the arrival of winter. Added roof shades serve as parasols or thermal blankets, depending on the season.
Another innovation implemented by the Weiss/Manfredi team was the form of the conservatory’s louvers. These fins are generally horizontal and can open at best halfway. Weiss explained, “Vertical shutters had never been done on anything like this scale.” These can open over 90 percent of their 10-foot length, enabling maximal airflow and providing a clear view in all directions “instead of one broken down by a thousand mullions.”
Countless conservatories have a pool at the center, but Longwood’s has three islands at its heart, crisscrossed by canals. Kristin Frederickson, principal at Reed Hilderbrand, described this design as a “topographical move” designed to reflect the “inseparable relationship among stone, water, and plants” in the Mediterranean. (The conservatory includes plants from Mediterranean Köppen zones around the world, with several recent arrivals from Australia.)
The circulation system consists of stone pavers that “float above the planted plane.” The bodies of water then terrace down beneath the water’s surface, a step—or steps—inspired by legendary Mughal Gardens at Lutyens’s Rashtrapati Bhavan in New Delhi. These canals will feature water lilies and seasonal aquatic plants.
While conservatories often host revolving plants that rotate out when they aren’t at their most picturesque—runway models on occasional display—the West Conservatory’s planting scheme is a more permanent composition, with 85 percent of the items planted intended to remain there year-round. Redman explained that it was a work of “deliberate design and craftsmanship” for the long term. There will be greater improvisation in hanging and trellised items, but the arrangement is intended to last.
Frederickson explained how Reed Hilderbrand achieved a balance between formality and informality, drawing upon both “orthogonal typologies” found in historic Italian and greater Mediterranean villa gardens. For this reason, the subsurface was all sorts of work. Weiss/Manfredi described it as the most complicated waterproofing the firm has ever done. This is all threaded around soil that is at least 3 feet deep and conceals ventilation of an extremely responsible sort: 300-foot-long earth ducts absorb soil temperatures to cool the interior in summer months, and geothermal sources and the steam from an onsite plant provide heat in winter. All the water used in the conservatory is harvested on-site.
The new West Conservatory represents the jewel in Longwood’s crown of recent renovations and architectural additions. A new arcade, also by Weiss/Manfredi, rings Peter Shepheard’s 1989 Waterlily Court to the east and a new administrative building (also by the firm) and the Bonsai Courtyard border to the north. The composition terminates in a new vista to the west of uncoiffed meadows that were previously obstructed by working greenhouses.
Burle Marx’s 1993 Cascade Garden, his only extant project in the U.S., was also relocated as part of this greater investment at Longwood. Sharon Loving, Longwood’s chief horticulture and facilities officer, recalled Burle Marx showing up to plan the spot and immediately forsaking his own planting plan to improvise from a buffet of plants the Gardens had provided from Brazil, California, and Florida. Loving described his process as akin to “painting with plants.”
The Cascade Garden was originally located in a constrained structure—Burle Marx’s Brazilian ebullience was cramped by a Victorian bustle. Plants too close to the walls suffered from both excess heat and frost, and a kapok tree grew gnarled and sideways against the ceiling. Manfredi explained that changing the structure much would be “presumptuous,” but the firm built a slightly taller and wider replacement to provide a more comfortable home for these plants. One hitch, Weiss explained, was keeping the Cascade Garden’s orientation to the sunlight and its configuration of topography identical to Burle Marx’s original vision. Save for an existing pathway that was marginally regraded to achieve ADA compliance, all other elements and plants were dutifully catalogued for precise reassembly.
Weiss spent extensive time traveling and researching in preparation for the West Conservatory commission. She was “seeing beautiful conservatories and beautiful gardens, but one had the sense that these were collections of passionately fabricated things, one thing after another.” Weiss/Manfredi’s aim was harmony among these built elements to, as Weiss explained, make these “one thing because of the other.”
Anthony Paletta is a writer living in Brooklyn.
Project Specifications
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- Architect: Weiss/Manfredi
- Landscape architect: Reed Hilderbrand
- Interior design: Weiss/Manfredi
- Structural engineering: MKA
- MEPFP engineering: JB&B
- Civil engineering: Pennoni
- Lighting design: Tillotson Design Associates
- Facade consultant: Front
- Historic structures: John Milner Architects
- Glazing contractor: Roschmann
- Glass: Glassbel
- Doors: Dawson
- Interior finishes: API
