Which production methods work best on a roof?
What are the main considerations before getting started?
Do I need to hire professionals to make my rooftop dream a reality?
What is the difference between a rooftop farm and garden?
How many rooftop farms exist in North America?
Is a rooftop farm a green roof?
What does certified organic mean?
Are most rooftop farms certified organic?
Does runoff from rooftop farms contain pollutants?
How are rooftop crops pollinated?
Will pests reach my rooftop?
How high are rooftop yields?
Is watering crops with rooftop runoff safe?
Can rooftop farming be profitable?
Is rooftop agriculture the future of urban food?
Farmers and gardeners grow food on rooftops using a variety of methods that vary in upfront investment, material longevity, and crop yields. In North America, growers most commonly and successfully produce food with containers, raised beds, row farms, and hydroponics. Containers fall to the low end of the cost/longevity/yield spectrum while greenhouse hydroponics falls to the high end.
You may need to collaborate with various professionals to get your project off the ground. Hiring a licensed structural engineer to evaluate your roof’s load capacity (including dead load, live load, snow load, and wind load, if applicable) is paramount in preventing a roof collapse. No project is too small to avoid this first step. For modest projects you may also decide to hire a plumber (to install a rooftop hose bib); an architect or contractor (to design and/or build roof access that meets local building codes and a roof deck with railing that distributes loads across the roof); and perhaps a landscape architect (to design your roof’s “living space”). Larger projects require the additional services of a green roof provider (to design any soil-based systems and related infrastructure, coordinate warranties with the roof’s waterproofing provider, ensure proper drainage, and facilitate construction); a greenhouse design engineer, if applicable (to design a rooftop greenhouse that meets wind load requirements and coordinate structural attachments); a knowledgeable contractor (to obtain building permits, crane materials to the roof, and build the rooftop farm as designed); and of course a farmer (to discuss intended crop varieties, long-term nutrient management strategies, supporting program requirements (e.g. composting, bee keeping), and yield expectations).
Urban agricultural experts can’t agree on the definitions of farm and garden. Some differentiate the two by size, others by food distribution or commercial engagement. EAT UP defines rooftop garden as that which produces food for self-consumption, gifting, or charity, and rooftop farm as that which sells food commercially or uses crops as ingredients in food that is sold (e.g. below in a restaurant or hotel).
Good question! The number of rooftop gardens increases every day and rooftop farms have popped up at an increasing rate during the past five years. There is currently no database of North American rooftop farms and gardens, so quantitative data is based on estimates.
A green roof is a layered, horizontal assembly of highly engineered materials planted with vegetation. Green roofs generally contain at least 3-inches of growth media and present many benefits including stormwater management. Rooftop row farms – agricultural roofs with contiguous growth media – are categorized as green roofs due to their buildup and performance characteristics. Rooftop farms that deploy raised beds and/or hydroponics are not green roofs. [Related posts: the next frontier]
Certified organic is a term given to foods or goods for which the production passed a third-party inspection by a state or nationally accredited certifying agent recognized by the USDA, Quality Assurance International, or other similar entity. Crops grown without the use of synthetic fertilizers, herbicides, and pesticides may not be labeled “organic” unless the third-party certification process is complete.
Most rooftop farms are not certified organic due to the financial cost of certification. The current exception is Uncommon Ground in Chicago, IL, which was certified organic in 2008 by Midwest Organic Services Association (MOSA). Most other rooftop farms practice chemical-free agriculture, meaning that no synthetic fertilizers, herbicides, or pesticides are used. Compost, animal manures, and other natural nutrients are applied to most soil-based rooftop farms, and integrated pest management (IPM) is a common practice for managing insect pests. North American organic certification entities do not currently recognize hydroponic production as an acceptable method for certification. Most commercial rooftop hydroponic greenhouses, however, do not use synthetic herbicides or pesticides. [Related posts: got organic? you betchya.]
Runoff from each rooftop farm contains varying levels of nitrogen and phosphorus, depending on the farm’s agricultural practices (e.g. fertilizer application rates). To avoid overloading our hydrologic system with nutrients, runoff management strategies – such as biofilters and recirculating irrigation systems – should be considered. Research and innovation is needed in this field, as it applies to rooftops.
Rooftop crops are pollinated the same way as ground-level crops: with bees (for most fruits and vegetables) and wind (for grains like corn and millet). The common honeybee, Apis mellifera, is a canopy dweller, and feels right at home on urban rooftops. Many rooftop farms keep bees to pollinate crops and provide honey, which can be sold for profit. Even hydroponic rooftop farms, such as Lufa Farms, in Montreal, QC and Gotham Greens, in Brooklyn, NY, keep bees within their greenhouses for crop pollination. [Related posts: rooftop beekeeping | rooftop beekeeping video]
In the world of agriculture there are good invertebrates (like ladybugs and earthworms) and bad invertebrates (like aphids and grubs). When conditions are just right and populations boom, the latter critters can devastate crops. Similarly, tasty crops often attract mammalian pests like groundhogs, deer, and squirrels, which seemingly can eat their weight in vegetables. Up on a roof, the immediate threat of pests is less. Invertebrate pests may be introduced accidentally through seedlings or compost brought up to the roof, or even by birds or on the bottoms of your shoes. Growing a diverse array of crops, a practice known as polyculture, will reduce the risk of pests devastating your whole farm or garden. To keep squirrels from reaching the goods, prune tree branches back that hang over your roof and use bird netting when necessary. [Related posts: the groundhog done it]
– content in progress – [Related posts: the full monty]
Several recent studies have investigated this question, including those published by the Journal of the NACAA (Haberland, M., M. Bakacs, S. Yergeau, 2013), Department of Ecology State of Washington (Winters, N., M. McCall, A. Kingfisher, 2014), and PLOS One (M. Tom, T. D. Fletcher, D. T. McCarthy, 2014). An 2015 Sightline Daily article summarizes these findings and suggests the following guidelines:
1| Do not water crops with runoff from treated wood-shake roofs; roofs treated with chemicals to kill moss, algae, or rot; roofs with zinc strips; copper roofs; or roofs with copper gutters
Rooftop agriculture is one, very up-and-coming, strand in the greater urban food web. People cultivate urban food in community gardens, urban farms, underutilized parkland, vacant lots, public right-of-ways, basements, walls, fire escapes, balconies, window ledges, and roofs. None of these locations will become the exclusive means of production. In fact, increasing the diversity of production increases the resilience of the urban food system. As cities densify and land values increase, however, production means and methods will shift to accommodate the city’s needs, and roofs will become increasingly important in meeting local food demands. No matter what the future brings, remember that the urban food system works and will always work in concert with our rural food systems, which play a critical role in our survival.