Rendering of completed West Conservatory.

Longwood Gardens, a botanical garden in Kennett Square, PA, recently reached a major milestone in its 17-acre transformation of the core area of conservatory gardens. The centerpiece and largest single element of Longwood Reimagined is a 32,000-square-foot glasshouse designed for sustainabiity by WEISS/MANFREDI, with gardens, pools, and fountains designed by Reed Hilderbrand. The glasshouse now has a fully constructed steel frame and is in the process of having nearly 2,000 glass panels installed, bringing the sweeping, deeply sensitive transformation nearer completion.

“The West Conservatory and the new Mediterranean Garden are capstones of 100 years of innovation in greenhouse and garden design at Longwood,” says Paul B. Redman, president and CEO of Longwood Gardens. “In 1921, Longwood founder Pierre S. du Pont opened one of the world’s great greenhouse structures, designed by J. Walter Cope. Since then, the conservatory complex has continued to grow and evolve with each generation adding state-of-the-art structures that incorporate new, innovative horticultural displays within.”

Rendering of an interior view of the West Conservatory.

Redman adds, “WEISS/MANFREDI has designed a building that not only is at the forefront of glass architecture, but leads the way in sustainability. The Mediterranean Garden designed by Reed Hilderbrand is adaptable to climate variations, and is especially noteworthy for its optimization of water usage in the oases of fountains, pools and plantings, that are being created.”

“Inspired by Pierre du Pont’s spirit of innovation, we have designed a living and breathing glass house, with walls and roofs that open and close in response to the weather, earth tubes that draw temperate air inside, and roof valleys that collect water, creating a sustainable destination we hope will become an enduring source of wonder and inspiration,” said principal architects Marion Weiss and Michael Manfredi.

Sustainable Design Elements
The West Conservatory employs a unique combination of passive and tempering strategies. Ten earth ducts—three feet in diameter, 250 feet long, and buried outside the conservatory—provide year-round passive tempering of fresh air in the conservatory. The tempered air is introduced at the pedestrian pathway to provide passive thermal comfort for occupants.

This innovative design means the building uses only natural ventilation, rather than relying on mechanical cooling, during warm months. Based on historic precedent and refined via advanced thermal conditioning modeling, the West Conservatory incorporates 10-foot-tall operable vertical façade openings along the building’s entire perimeter. Outside air entering through these vertical openings flushes out heat buildup, with hotter air rising and escaping through the roof openings, which comprise 15-20% of the overhead surface area. Additionally, an automated shading system is deployed to reduce solar heat gain during the hottest days of the summer. During cold months, the shading system also acts as a thermal blanket, operating during evening hours to trap heat inside and reduce radiative heat loss.

Water Conservation & Critical Plant Selections
Longwood Gardens, renowned for its fountains, reinterprets that tradition as part of Longwood Reimagined. Set on an immense plane of water, the West Conservatory designed by WEISS/MANFREDI welcomes guests into a beautiful floating garden of planted islands, canals, and low fountains designed by Reed Hilderbrand.

Rendering of water elements in the West Conservatory.

Yet underpinning this experience of water is a sophisticated water conservation system that collects stormwater from the roofs of the West Conservatory and education and administration building and captures the overflow from the Gardens’ exterior water features. Water collected from these systems will be stored in large underground tanks and later recirculated through the water features and portions of the restrooms.

The garden is inspired by Mediterranean-climate ecosystems, which are known for hot, dry summers and cool, wet winters, and the regions’ historic traditions of designing thoughtful, expressive water-wise gardens. The extensive plant palette will consist of iconic plants from six representative geographic areas including the Mediterranean Basin, the Cape Region of South Africa, coastal California, Central Chile, Southwestern Australia, and South Australia. Agaves, (Agave ‘Reginae x ovatifolia’), Aloes (Aloe ‘Johnson’s Hybrid’), Blueblossom (Ceanothus thyrsiflorus), and Breath of Heaven (Coleonema pulchellum) will hug the ground of the West Conservatory. Taller plants like Cypress (Cupressus sempervirens), Laurus (Laurus nobilis), Acacia (Acacia salicina), and 100-year-old olive trees will rise dramatically in the soaring space. Over the past year, Reed Hilderbrand and Longwood Gardens have traveled across the U.S. to scout and tag plants at the nation’s leading nurseries. The mature olive trees, which will be transplanted into the garden, have been sourced from groves in California.

Spaces Designed for Preservation and With Purpose

New Glass House for Historic Roberto Burle Marx Cascade Garden.

Other elements of the Longwood Reimagined project which are well underway include the new education and administration building, as well as the new restaurant and event spaces. Outside the historic Main Conservatory, 28 Yellowwoods (Cladrastis kentukea) will be planted in an allée at the eastern end of the Grand Promenade. This spring, Longwood will begin construction of a custom-designed conservatory to preserve the design of landscape architect’s Roberto Burle Marx’s only extant garden in North America. The Cascade Garden represents the first time a historic garden has ever been relocated and reconstructed. The garden by Burle Marx, first developed for Longwood in a retrofitted conservatory building in 1992, will now have a new jewel box-like glass house allowing it to thrive for many decades to come.

Photos: Courtesy of WEISS/MANFREDI with Reed Hilderbrand for Longwood Gardens

About Longwood Gardens
In 1906, industrialist Pierre S. du Pont (1870-1954) purchased a small farm near Kennett Square, PA, to save a collection of historic trees from being sold for lumber. Today, Longwood Gardens is one of the world’s great horticultural displays, encompassing 1,100 acres of gardens, woodlands, meadows, fountains, a 10,010-pipe Aeolian organ, and grand conservatory.

For more on the project, see “Longwood Gardens Transforming Renowned Conservatory Grounds.”

Another horticultural attraction in the area is the Philadelphia Flower Show. Read about last year’s event: “STIHL Sponsors Philadelphia Flower Show Highlighting Innovative Landscapers.”

Read the full article “New Glasshouse At Longwood Gardens Highlights Sustainability” on Turf Magazine.