Under the Bleachers: Beneath Longwood Gardens’ new terraced landform, sustainability blooms.
Every year almost 1 million people visit Longwood Gardens, the horticultural paradise that Pierre S. du Pont founded in 1906. This month visitors will start strolling the Kennett Square, Pennsylvania, property in earnest, spying tulips and foxglove, while orchids, caladiums, and snapdragons await them inside Longwood’s iconic 4.5-acre conservatory. There’s another surprise for botany buffs as they make their way from outdoors to within.
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In October Longwood dedicated its new East Conservatory Plaza, designed by Richmond Upon Thames–based landscape architect Kim Wilkie with London-based Michaelis Boyd Associates and local project designers Wells Appel Landscape Architects and FMG Architects. This portion of the conservatory underwent renovation six years ago, but the adjacent exterior space had not been addressed for egress, says director of facilities Mark Winnicki. The plaza fulfills that purpose, while also providing a venue for events and lounging.
Wilkie is well known for sculpting earth to dramatic effect—for the landform Orpheus, he inserted an inverted grass pyramid into the grounds of the famous British garden Boughton. The Longwood Gardens project, Wilkie’s first terraced landform in the U.S., features five tiers that emerge from the southern part of the site, gradually rising and sweeping around the plaza to join the conservatory. The structure appears as a partly submerged amphitheater overtaken by a blanket of Kentucky bluegrass and Tall fescue. (Due to the slope of the terraces, overhead and subsurface irrigation systems are watering the grass.) From the plaza’s southernmost point, one can also glimpse portals, like greenhouse roofs, dotting the top of the landform.
The latticed glass hints that Wilkie’s amphitheater has an interior, and attendees of blockbuster events like the choreographed show Fireworks and Fountains will be grateful for the 17 unisex single-user restrooms inside. The lavatories flank a double-loaded corridor, and each room is a freestanding, jug-shaped volume that terminates in an oculus. Winnicki says that the subterranean placement of half of these so-called “pods,” the thermal mass of poured concrete, and generous insulation equate to an effective thermal blanket, although performance figures were not available as of press time.
The more expansive glass roofs admit daylight into the corridor, which follows the curve of the landform in plan. A stainless-steel door marks each lavatory dome, and between them, Wilkie has conceived the largest indoor living wall in North America, comprising 4,072 square feet. The majority of these 47,000 vertically installed plants are fern varieties, which were chosen and arranged according to the wide range of daylighting conditions from floor to ceiling.
Common to all plant species is the infrastructure put into place to hydrate them. Irrigation tubing “is suspended from the wall, and water runs through coconut fiber to the individual planter boxes. The fiber stands about three inches from the wall, so water never sprays on it,” Winnicki explains. Digital controls channel and withhold water according to those disparate light conditions, and moisture sensors help staff gardeners monitor saturation and to tweak the system between days and seasons. Speaking of seasons, Winnicki says the vegetated wall diffuses the glare of summer sun, and naturally humidifies the interior come winter.
Human intervention helps modify the interior climate during extreme conditions. The glass roofs may be opened to improve ventilation on hot days, for example. And in deepest cold, Wilkie’s design team took a cue from Longwood itself. The conservatory runs an innovative root-zone heating system, which concentrates heat on roots and prevents the ambient air from hitting uncomfortable temperatures. Underneath East Conservatory Plaza, a hydronic closed loop in the floor efficiently warms visitors’ own trunks and branches.
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