Hoping for a City Full of Farms on Rooftops
by Anne Raver
New York Times, August 4, 2002
NEW YORKERS and other city people may be used to seeing tomatoes and peppers in big pots on the roof, but what about a little farm growing right out of the tar beach?
"This is our kitchen garden," said Leslie Hoffman, the executive director of the Earth Pledge Foundation, a nonprofit group that promotes sustainable agriculture and environmental preservation. She crunched across the pebbly ground of her vegetable plot, where tomatoes, eggplants, sweet and hot peppers, lettuce and squash, to say nothing of a river of herbs and flowers, are flourishing in a strange soil mix covering about 700 square feet of the roof of a 1902 town house at 149 East 38th Street in Manhattan.
She picked up a few of the smooth little pebbles. "This is called expanded slate," she said. "It's like puffed stone."
The stones, formed by volcanic ash, do seem as light as air, and they hold moisture. Mixed with 15 percent compost and 30 percent sand, this porous soil (www.stalite.com, phone 877-737-6284), has to be fertilized about once a month. The fertilizer is fish emulsion, but not of the usual kind.
"Most fish emulsion is rotten fish guts," Ms. Hoffman said. "It's cooked, which kills the enzymes and proteins." This fertilizer, not yet available commercially, is cold-processed fish waste, alive with the enzymes from shark innards.
By the look of the tomatoes ripening on the vines, these plants seem to be thriving on fish and fake soil, with a reservoir of rainwater beneath their roots. When rain is scarce, a drip irrigation system is used.
"We had a bumper crop of arugula," Ms. Hoffman said. "And zucchinis and yellow squash. I got six off the roof on Friday."
Heat-loving herbs and flowers - including basil, sage, lavender, tarragon and verbena, bee balm, catmint, day lilies - are flourishing among the vegetables.
Earth Pledge may be familiar to many, thanks to its virtual farmers' market, www.farmtotable.org, which connects more than 120 organic farmers and their fresh produce with consumers looking for local foods, unusual recipes and the latest events on food-related issues.
Last month, it began a Green Roof Initiative with a conference of more than 100 people, from landscape architects to investment bankers wanting to know how to build greener, cooler, cleaner cities. Though Germans have been growing green roofs for years, Portland, Ore., Toronto and Chicago - which last summer installed a $1 million green roof, covering half a block, on top of its city hall - are leaders in North America.
Earth Pledge, which was founded in 1991 by Theodore W. Kheel, the lawyer and labor mediator, to promote interest in the principles of the 1992 Rio Earth Summit, hopes to turn New York roofs into green oases that not only feed its citizens but keep them cool.
Green roofs can combat the urban heat island effect, Ms. Hoffman said. All the stone, brick and blacktop absorb so much heat that cities are six to eight degrees hotter than surrounding suburbs. Energy experts estimate that New York could save as much as $16 million a year in energy costs by growing green roofs, which not only cool buildings in summer, but insulate them in winter.
Designed by Diana Balmori, a landscape architect based in New Haven who also teaches environmental design at Yale University, this green roof has an ingenious layered construction, manufactured by American Hydrotech of Chicago (www.hydrotechusa.com, 800-877-6125), which allows for the absorption and retention of rainwater without leaking through the roof. It also keeps roots from breaking through the waterproof membrane that covers the deck. The layering, from the deck up, begins with a seamless
waterproof membrane made of rubberized asphalt, which is applied to the deck as a hot fluid. On top of that a root barrier, polystyrene insulation, drain mat (resembling an upside-down egg crate) for water retention and aeration and finally, 3 to 12 inches of soil mix, depending on the crop, like shallow-rooted mesclun, or deep-rooted tomatoes.
Ms. Hoffman said she does not know the actual cost of this cutting-edge system, because most of the materials and labor were donated. But American Hydrotech estimates that the layered system, from waterproof mat to high-tech soil mix, could cost $10 to $15 a foot, if you do it yourself; $15 to $30 if it's a union job.
The Green Pledge garden has custom-made stainless steel planters bordering two sides of the roof. These Cadillacs, 18 inches deep and lined with plastic foam for heat insulation, form an elegant $20,000 wall around the roof. They are filled with rosemary, oregano, summer savory, cucumbers and pole beans winding themselves up steel posts, which hint of trelliswork to come. (To see the green roof, call the Earth Pledge Foundation at 212-725-6611 or visit www.earthpledge.org.)
This green roof will collect about 75 percent of the water that falls on it, Ms. Hoffman said. That means a lot less water flowing into Manhattan's sewer system. "Most down-spouts are connected to the same plumbing infrastructure as toilets and sinks," Ms. Hoffman said. So New York is treating all that rainwater the same as sewage. What a waste. And when it rains in torrents, that water floods the city's sewage system and can send raw sewage straight into the rivers.
"Imagine a city of green roofs," she said. There wouldn't be so much overflow. And all those air-conditioners wouldn't be burning quite as much energy.
Earth Pledge is planning a fall conference for government officials and others to draw up a plan for building more green roofs in New York City. Ms. Hoffman has her own vision for the redevelopment of the World Trade Center site: kitchen gardens on all the roofs.