By Michelle Sutton
Their campuses are adjacent, but their landscaping approaches are strikingly different. While Syracuse University uses a more conventional palette of plant hybrids and non-natives (for example, widespread use of orange petunias to celebrate the school color), the College of Environmental Science and Forestry (SUNY ESF) strives to follow a native-plant-community approach to its landscaping (using, for example, native goldenrods, oaks, sumacs, and sedges).
Thus, it made sense that in 2010, when it came time to design a new 9,400-square-foot green roof, SUNY ESF wanted to use the opportunity to explore using plants from New York natural plant communities. In so doing, common and very rare plants within those communities provide a richer research and teaching environment than could be afforded by the seas of sedums and other succulents that usually dominate green roofs.
The new SUNY ESF green roof is an aesthetically pleasing addition to the open space of the campus, and in its exceptional plant diversity. The green roof also provides habitat for a wider range of insects and other animals for study. It is a versatile outdoor classroom and gathering place atop SUNY ESF’s award-winning LEED Platinum Certified Gateway Center Building (completed in 2013). The green roof was designed to contribute to the Gateway Center’s highly efficient stormwater management system and to aid in regulating building temperature.
Significant funding for planting and hydrologic monitoring of the installation came from the New York State Environmental Facilities Corporation (EFC), which is the arm of Governor Cuomo’s administration that provides low-cost financing for local wastewater and drinking water infrastructure.
Rugged for the rooftop
The lead landscape architect for the project was Darren Damone of Philadelphia-based firm Andropogon Associates. In order to determine the best plant species for the roof, Damone and his associates worked closely with faculty at SUNY ESF, including Distinguished Teaching Professor of Environmental and Forest Biology, Don Leopold (author of Native Plants of the Northeast: A Guide for Gardening and Conservation and Trees of New York: Native and Naturalized) and Associate Professor of Landscape Architecture, Timothy Toland, who specializes in sustainability and holistic systems design.
In thinking about the conditions that are typical for a rooftop garden, and in their case a west-facing one, the Andropogon/SUNY ESF team recognized that it needed plants that would endure extremes of temperature, wind and moisture. To minimize future maintenance, the team sought plants that can tolerate low soil fertility/low organic matter and shallow soils. Drought tolerance was also key, as the intent was to have the plants function as they would in their native environment, without any supplemental irrigation.
The team chose two natural plant communities adapted to these very conditions: the Eastern Ontario Dune community, a windy and dry habitat extending 17 miles along Lake Ontario, and the Alvar Pavement Barren community, found in limited pockets north of the Great Lake Dunes, to the northwest of Watertown, N.Y. Alvar community plants grow in low-fertility soil with a high pH and, despite the shallow soils they inhabit, tolerate the drought of summer but also the seasonal wetness of spring. With these communities, the team found an ideal match for the rooftop conditions.
It would be no small feat to responsibly source these plants — some of which grow natively only in the Eastern Ontario Dune and Alvar Pavement Barren ecosystems. Motherplants Ltd., a green roof plants specialty grower now based out of Princeton, Ontario (then based out of Ithaca, N.Y.) was contracted to propagate and procure the plants.
But first, the design team and SUNY ESF faculty developed a set of rigorous plant trial protocols, and constructed a series of test frames on an adjacent building roof to mimic growing conditions. (Carlisle SynTec donated materials for the initial test frames.)
“The group as a whole was fairly confident that the plants would perform well, but the design team needed to validate that we could deliver a successful and sustainable design solution to the client,” said Damone.
In 2010, Leopold and colleagues obtained cuttings, seeds and plugs, and involved students in research involving planting each species at varying soil depth, media and spacing. They collected three seasons of data, which gave evidence that plants from these specific plant communities did well in this specific unirrigated, rooftop environment.
The Andropogon Associates planting plan called for the Eastern Ontario Dune plant community to be sited on three sides of the green roof perimeter. Dune plants that are thriving there include American beach grass (Ammophila breviligulata), Canada wild rye (Elymus Canadensis) and the heartleaf willow (Salix cordata). The internal, more protected beds are populated with the Alvar community plants, which include hairy beardtongue (Penstemon hirsutus), golden alexanders (Zizia aurea), northern prairie dropseed (Sporobolus heterolepis), smooth rose (Rosa blanda) and various sedges (Carex spp.).
Motherplants brought in 3,000 plugs in November 2012, the earliest the roof could be readied for planting. Mark Winterer, co-owner of Recover Green Roofs, who collaborated on the planting, said, “We had to wait for the ground to thaw every morning before we could plant.” However, planting the plugs in a dormant state turned out to have an advantage — their moisture requirements were low; and with supplemental water provided for just the first few weeks after planting, the vast majority of the plants came through the winter and established well.
A highly porous, lightweight growing medium was conveyed to the site by a blower truck; it was intended to have less than 10 percent by mass organic matter (OM), because overly fertile soil would preference the growth of certain species over others, which would have upset the plant-community balance the designers sought. (Based on observing overly vigorous growth of some plants, Leopold later commented that 5 percent or less OM would have worked better.)
The earth was sculpted with sections of expanded polystyrene geofoam to provide some undulations for aesthetic and microclimate purposes. Jute erosion control mat, while difficult to install on a windy rooftop in November, turned out to be extremely important in stabilizing the friable growing medium against erosion. Irregular flagstone slabs mimicked the limestone, and pavement found in the Alvar environment and provide entry points for teachers and students to gain a closer look at the plants. In terms of the planting, Toland said, “The patterning of the species was based on massing for aesthetic impact and to aid in monitoring.”
Three-plus years after installation, the green roof plant communities are thriving, and the beautiful outdoor gathering, teaching, and research space is fulfilling its mission. Leopold said, “Given that we are not aware of any similar planting on any other green roof in the U.S., I have been very pleased that the plant species that we selected have generally thrived under these very challenging growing conditions.”
Hydrologic monitoring has been conducted by SUNY ESF Associate Professor of Environmental Resources Engineering Doug Daley and others to document that the green roof fulfills its stormwater management objectives as well.
SUNY ESF and Andropogon Associates received the 2014 Merit Award from the New York Chapter of the American Society of Landscape Architects for the Gateway Center Green Roof. The green roof is open to the public during regular business hours, and is not to be missed if you find yourself in the vicinity of Syracuse, N.Y.
Michelle Sutton (michellejudysutton.com) is a horticulturist, writer, and editor.
Main photo above courtesy Andropogon Associates