TAKE ONE
Gardener News Serving the Agricultural, Gardening and Landscaping Communities GARDENERNEWS.COM
November 2018
TAKE ONE No. 187
Green Roof at Cook’s Market
Tom Castronovo/Photo
Bruce Crawford, Director of the Rutgers Gardens on the G. H. Cook Campus at Rutgers, the State University of New Jersey, proudly stands under the Rutgers Gardens sign in front of the garden’s new green roof.
People often ask, what is a Green Roof? It is not a new concept, but it is new to many folks who often believe it has something to do with solar panels. Green Roofs are living roofs, featuring a layer of lightweight soil that is planted with an assortment of suitable vegetation. The advantages of such roofs have been appreciated since medieval times throughout Europe; sedums and other drought-tolerant plants would volunteer on roofs, helping to insulate the homes from summer’s heat or winter’s chill. Today, living roofs are more scientifically based, and depending upon the soil depth, Green Roofs are broken down into Extensive and Intensive Roofs. An Extensive Roof features a thin layer of engineered soil, typically four inches or less, while an Intensive Roof has greater soil depths, allowing for a broader palette of plant materials to be incorporated into the design. The Green Roof at Rutgers Gardens is located on top of Cook’s Market, the structure located at the entrance to the Gardens that hosts the Farm Market every Friday from 11 a.m. to 5 p.m. This year also celebrates the
10th anniversary of the Farm Market! The galvanized steel structure has an Intensive Roof, with five to seven inches of soil placed above two inches of gravel for drainage. The soil is a custom blend of mushroom compost mixed with aggregates of calcined clay and shale. This blend and depth will support sweeps of Little Bluestem Grass (Schizachyrium scoparium) and Autumn Moor Grass (Seslaria autumnalis) that will act as “green mulch.” Emerging through the grassy sweeps will be a number of flowering plants, including Pale Purple Cone Flower (Echinacea pallida), Beebalm (Monarda bradburiana), Grass-leaved Goldenrod (Euthamia graminifolia) and Rattlesnake Master (Eryngium yuccifolium). The only woody plant added to the roof is a low growing form of Fragrant Sumac (Rhus aromatica “Gro-low”). It features stunning red fall color and it will spill nicely over the edges of the roof, adding softer lines to the rooftop. With the exception of the Autumn Moor Grass, all of these plants are native to Eastern North America, providing not only color to the rooftop, but also food and habitat for our native pollinators, caterpillars and
insects. Some of the selections are experimental – to see if they will survive the rigors of living on a roof – while others are proven survivors. The plant selection is a collaboration between Rutgers Gardens and the Morris Arboretum, which also has a similar structure with a green roof. Since there is not a lengthy list of which plants do best on roofs, especially those that do not have a heated area beneath, testing plants in both locations will better illustrate the impact of weather conditions on the plant material. Although the plants are adapted to dry and windy sites, an irrigation system was also installed to support the material during prolonged periods of drought. Aside from appearing more attractive than conventional roofs, Green Roofs have the advantage of slowing stormwater discharge, allowing it to drain from the roof over a two- to three-day period, versus just during the storm. This allows the structure to be far more environmentally sensitive, since the slow discharge of storm water reduces the potential erosion of local stream banks and works far more efficiently with rain gardens that promote deep water recharge. These roofs also have the advantage (Cont. on Page 13)