Eli Zabar’s greenhouse operation in the Upper East Side of Manhattan illustrates the potential for integrating commercial-scale food production onto rooftops. Significantly more food can be produced over a much longer growing season in rooftop greenhouse operations than with open-air green roofs and container gardens. Zabar’s idea for the greenhouses emerged around 1995 from two of his interests. He wanted to stretch the season during which he could sell fresh, local tomatoes, and he wanted to use the waste heat from a bakery he operates. “When I put the two ideas together, the light bulb went off,” Zabar told EBN. He currently manages four greenhouses, the largest 40′ x 100′ (12 x 30 m), with a full-time greenhouse staff of two. Since he built the first of his rooftop greenhouses, Zabar has always grown in soil. While he has visited lots of successful hydroponic greenhouse operations, he believes that produce grown in soil tastes better. “I’m not interested in hydroponics,” he said. With soil-based growing, he’s also able to make use of compost that he produces on the roof using discards from his market. He has an eight-foot (2.4 m) diameter drum with an auger that is turned regularly to mix the compost. His recipe for compost includes sawdust and bread from his bakery (which supplies about 1,000 restaurants in the city). Zabar would like to compost more of his organic waste but can’t. “We could do a ton more, but there’s a space limitation,” he said. Ducts from his bakery ovens heat the rooftop greenhouses, providing all of the needed heat for his lettuces and herbs. For tomatoes, he has to supplement that heat to maintain an optimal temperature of 75°F (24°C).zabar-Greenhouse

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