Permaculture landscaping
Conventional practice in commercial development of all types is to install generic shrubs and shade trees in a sterile landscape of mounded mulch and turf. One can walk out of almost any office building, school, hotel, or restaurant coast-to-coast, and see the same landscape. Why not devote some of that landscaping cost and effort to trees and shrubs that bear fruit? This is one of the ideas of permaculture, a landscaping practice (the word derived from “permanent” and “agriculture”) pioneered by Bill Mollison of Australia.
While there are plenty of examples of homeowners replacing their lawns with edible landscapes (and a number of excellent books on this topic), EBN was—remarkably—unable to find any examples of commercial buildings whose owners implemented an edible landscaping strategy. Why can’t employees at a Florida office complex go outside for a mid-afternoon stroll and pick a ripe orange from a well-managed landscape of dwarf citrus trees? Why can’t schoolchildren and teachers in Yakima, Washington, pick cherries, raspberries, and apples during recess? Wouldn’t this be the “low-hanging fruit” of a transition to more localized food production?
Farming Our Rooftops
For an article in 1998 on low-slope roofing (see EBN Vol. 7, No. 10), we calculated that the nation’s 4.8 million commercial buildings had about 1,400 square miles (360,000 ha) of roof, most of which is nearly flat—this is an area larger than the state of Rhode Island. While lots of these roofs are shaded by neighboring buildings, are structurally inadequate to support rooftop activity, or are otherwise inappropriate for use, there are lots of buildings where rooftop gardens or greenhouses could very effectively be used for food production.
Green roofs and container farming
Most green roofs today are created to manage stormwater flows, to reduce the urban heat island effect, to save energy, or to create attractive green spaces. Green roofs can also provide “farmland.”
Portland, Oregon, has been a leader in advancing green roofs (eco-roofs, as they are called locally), so it’s no surprise that some examples of food-producing green roofs can be found there. One of them is the Burnside Rocket building, a new mixed-use green building in the Lower Burnside neighborhood of the city. On the roof, Marc Boucher-Colbert manages about 1,000 ft2 (100 m2) of garden space. Included in this growing space are two small sections of intensive green roof ( intensive green roofs have deeper soil than the more common, extensive green roofs—which are typically planted with sedums), six 3′ x 9′ (0.9 x 2.7 m) raised beds, and 39 circular plastic planters made from “kiddie” pools, each about four feet (1.2 m) in diameter. For two years, Boucher-Colbert has been growing a variety of produce for the Rocket Restaurant located on the first floor of the building. (Unfortunately, the restaurant closed in late 2008.)
Boucher-Colbert uses a variety of soil amendments for his organically managed gardens, including kelp meal, glacial rock dust, bone meal, blood, worm casings, and commercially available organic fertilizer. His soil depths vary from about 3″ (80 mm) for the round planter beds to 18″ (460 mm) in the raised beds. When necessary, he waters beds with a solution including a fish-emulsion and kelp organic fertilizer. His goal is year-round food production, offering chefs a variety of healthy, fresh, seasonally appropriate produce. Along with a variety of herbs, Boucher-Colbert has produced lettuce, arugula, tomatoes, peppers, eggplant, summer squash, cucumbers, and various specialty vegetables, such as golden-podded peas.
Using green roofs for food production is not without challenges. Along with the structural loading issues (Boucher-Colbert cautions that one should not follow his example without a thorough inspection by a structural engineer), easy access to the roof is critical. In a multifamily residential or commercial building, occupants may not want urban farmers traipsing with wheelbarrows of fertilizer and muddy tools through a public lobby.
Rooftop greenhouses with soil
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).
Rooftop hydroponic greenhouses
While Eli Zabar is a strong proponent of soil-based growing, much of the recent interest in rooftop greenhouses has focused on hydroponics, which involves growing plants in nutrient-rich water. This method offers a number of distinct advantages in rooftop applications.
Benjamin Linsley of BrightFarm Systems in New York City (www.brightfarmsystems.com) consults on rooftop greenhouses and claims that hydroponic management is 10–20 times more productive than field agriculture, with far lower water use and higher reliability. After developing the “Science Barge,” a demonstration project with a floating farming component that operated along the Manhattan waterfront in the summers of 2007 and 2008, he shifted his attention to rooftop hydroponic greenhouses. BrightFarm Systems has several hydroponic rooftop greenhouse projects in the queue for construction during the first half of 2009, he told EBN, and another 15 projects that stand a good chance of moving forward before the end of 2010.
There are three basic hydroponic techniques. With raft hydroponics, plants are grown on a floating raft with roots extending into nutrient media. This approach adds considerable weight, depending on the depth of the hydroponic tanks, so it is most commonly used in ground-mounted greenhouses, not rooftop applications.
Nutrient film technique (NFT) hydroponics is used for leafy plants, such as lettuce, spinach, and basil; the nutrient solution is circulated through hollow plastic channels that support the plants, and the plant roots hug the surface of the channel to absorb the water and nutrients. This is a recirculation technique; nutrients are added to the solution in the reservoir. Of relevance to rooftop applications is the lighter weight of NFT compared with other hydroponic approaches or soil. The primary weight is the reservoir, which can be located on a portion of the roof that has adequate structural reinforcement—so the entire roof structure may not need to be strengthened.
Dutch bucket hydroponics involves buckets or bags filled with an inert media—such as perlite, vermiculite, or mineral wool—through which the nutrient solution is circulated; this system is used primarily for tomatoes, peppers, root vegetables, and other plants with more substantial stems. In this type of facility, there is greater weight spread throughout the greenhouse, both from the buckets and the plants themselves, which can be quite heavy when fully grown.
With Dutch Bucket hydroponics, nutrient solution is trickled through buckets or sacks filled with an inert growing medium.
Hydroponic farming necessitates precise management—including careful measurement of nutrient concentrations and adjustment of flow rates. Due to its chemical nature, hydroponics has traditionally been harder to manage organically than soil-based agriculture; hydroponic growers need to know precisely how much of various nutrients are being added to the growing solution, and that’s easier to do with synthetic fertilizers. Michael Christian, president of American Hydroponics in Arcata, California (www.amhydro.com), one of the leading suppliers of hydroponic equipment, told EBN that the hydroponic farming movement has so far been less focused on organic methods. That is beginning to change, though, particularly in Europe.
