Space-saving, low-input, pest-free: vertical farming is often regarded as a solution to many of conventional agriculture’s woes. But the findings of a new study draw a question mark over its prospects, showing in lettuce farm experiments that vertical agriculture had higher environmental impacts than conventional in all but one category.

Even when it came to land-use where high-rising vertical farms would appear to have the edge, the study found that in fact these farms had twice the impact of lettuces farmed on conventional fields.

The revelations emerged from a comparison between three lettuce field farms grown variously on mineral soil and peat fields in the UK and Spain, and a four-storey vertical farm where lettuce was raised hydroponically in a UK city. The researchers conducted a lifecycle analysis to examine the environmental impacts of each farm, looking at the land, water, and fuel use entwined with each one, as well as emissions and nutrient pollution. This study is also the first of its kind to factor the soil emissions resulting from field farming into the life cycle analysis, the researchers say.

What immediately stood out was that water use was the only category where the vertical lettuce farm had a smaller footprint than the lettuce fields in the UK and Spain. Water use was eight times lower than on the most water-intensive lettuce farm in Spain.