Urban Crops can have Higher Yields than Conventional Farming

As urban populations boom, urban agriculture is increasingly looked to as a local food source and a way to help combat inequitable food access. But little is known about how productive urban agriculture is compared to conventional, rural farming. A new study digs in, finding urban gardeners and hydroponics can meet and sometimes exceed the yields of rural farms.

"Despite its growing popularity, there's still quite a lot we don't know about urban agriculture, like whether the yields are similar to conventional agriculture, or even what crops are commonly grown," says Florian Payen, an environmental scientist at Lancaster University and lead author of the study, published today in AGU's journal Earth's Future.

The new study compiles studies on urban agriculture from 53 countries to find out which crops grow well in cities, what growing methods are most effective, and what spaces can be utilized for growing. The researchers find that urban yields for some crops, like cucumbers, tubers and lettuces, are two to four times higher than conventional farming. Many other urban crops studied are produced at similar or higher rates than in rural settings. Cost efficiency remains an open but important question.

Most studies on urban agriculture have focused on green spaces, such as private and community gardens, parks and field growing operations. Payen's work includes "gray" spaces—places in cities that are already built but could be used for growing, such as rooftops and building facades. In both green and gray spaces, the study examines a suite of crops grown in soils versus hydroponics, horizontal versus vertical farming, and natural versus controlled conditions.

"Surprisingly, there were few differences between overall yields in indoor spaces and outdoor green spaces, but there were clear differences in the suitability of crop types to different gray spaces," Payen says. Certain crops like lettuces, kale and broccoli are more naturally suited to be grown vertically in indoor spaces than others. "You can't exactly stack up apple trees in a five- or ten-layer high growth chamber," he says, "though we did find one study that managed to grow wheat stacked up like that."