While rooftop dining has become a popular past time in many cities around the world, the use of roof space has also gained popularity among urban farmers.
In Paris, one grower has blended aeroponics with vertical farming on city rooftops to understand the potential to produce food for urban communities.
Like hydroponic farming, aeroponics is characterised by a lack of soil. But instead of plant roots being submerged in water they receive a continuous fine spray of water and essential nutrients.
Early adopters of the movement say that there are significant advantages to aeroponics. Crops yield more produce than conventionally grown counterparts, with one study indicating that capsicums yielded 65% more when grown aeroponically. Water use is up to 90% lower than other farming methods, and the use of pesticides and fungicides is also significantly reduced.
According to Pascal Hardy, the brains behind the Paris experiment, the benefits don’t end there.
“It uses less space. An ordinary intensive farm can grow nine salads per square metre of soil; I can grow 50 in a single tower. You can select crop varieties for their flavour, not their resistance to the transport and storage chain, and you can pick them when they’re really at their best, and not before,” he said.
Mr Hardy started growing food in vertical towers on the rooftop of his own apartment building five years ago. Today, his project spans several buildings including a research and development site on top of a gym and the most recent acquisition, 14,000 square feet atop a new exhibition building in the southern 15th arrondissement.
The new site is now the world’s largest urban rooftop farm, and the first crops of strawberries, basil, sage, peppermint, lettuces, cherry tomatoes, and eggplant have recently been harvested.
In full production, this site alone will yield up to 1000kg of produce per day.
Nature Urbaine is already supplying produce to local residents, caterers and wholesalers, offering a further benefit to the system.
“[Food is] produced up here, and sold locally, just down there. It barely travels at all,” he said.
“I don’t much like the fact that [conventionally-grown food] travelled an average of 2,000 refrigerated kilometres to my plate, that their quality is so poor because the varieties are selected for their capacity to withstand that journey, or that 80% of the price I pay goes to the wholesales and transport companies, not the producers.”
With wholesaling and freight costs all but eliminated, there are potential margin gains to be had. Sold online, direct to the consumer, Nature Urbaine’s produce is marketed at a price between conventionally-grown and organic foods. Set up costs are modest – around AUD$200 a square metre. Roof top farms benefit from free sunshine, meaning electricity consumption is a fraction of the energy used by other emerging indoor farming models.
The main restriction is the amount of available roof top space, and the price that owners may start to charge as demand rises.
For Mr Hardy, the potential benefits of his farming system surpass the economics to offer urban communities a sustainable approach to food production.
“It is a clean, productive and sustainable model of agriculture that can in time make a real contribution to the resilience – social, economic and also environmental – of the kind of big cities where most of humanity now lives,” he said.
“And look: it really works.”