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.

But beyond water-efficiency, the benefits of the vertical lettuce farms became less clear. Most striking was the large emissions footprint of vertical farms, which was bigger compared to all the field farms. In some scenarios vertical farming produced eight times more emissions than the most impactful farm field, generating 4.71 kilograms of CO2 equivalent per kilogram of lettuce, compared to just 0.59 kilos on field farms. 

These figures were even more striking when considering that vertical farms were being compared with fields where there is plenty of emissions-intensive activity going on: from fuel to fertilizers, and the substantial soil emissions associated with crop production on fields, especially those cultivated on carbon-rich peat soils. And yet, all this was eclipsed by the enormous amounts of electricity required to keep vertical lettuce farms well-lit, heated, and cooled, which is primarily what drove their huge energy footprint. 

Even when renewable energy was used to power these activities—bringing down emission to 0.93 kilograms of CO2eq per kilo of lettuce—vertical lettuce farms still had a higher greenhouse gas footprint than field farms because of carbon-intensive activities embedded across other aspects of their lifecycle. 

Beyond the emissions footprint the most surprising, and altogether unintuitive, result was that vertical farms had a greater land-use impact than field farms. This came down to the roots of the plants—literally. In vertical farms, lettuce plants are often sown in natural casings made of jute fibers, which come from a tall grass crop that’s cultivated in tropical regions. 

The ubiquitous plugs therefore link the lettuce industry to vast farms that in turn take up large amounts of land (where cultivation also adds its own emissions impact). In fact, the land use associated with vertical lettuce farming was two times higher than with greens farmed in the field. Indoor lettuce farms also had a higher acidification impact on water bodies, likely because of fertilizing practices on the jute farms that are tied to vertical lettuce farming. 

One solution could be to replace the jute with coir, a similarly fibrous material from coconuts, the research team says. That one move would reduce these enormous land-use impacts and bring them down to levels far below the field farms. 

The fact that the researchers delve into solutions shows they still believe vertical lettuce farming has prospects as an alternative to the field. There is one significant draw: its remarkable yields. In the study, vertical lettuce farms produced 97.3 kilos of lettuce per square meter, compared to just 3.3 kilos in the field farms. Meaning that vertical farms produced over 20 times more food than conventional fields. 

If vertical lettuce farming could be decoupled from its other land-use impacts, that land-sparing potential could become a huge boon for nature, helping to free up farmland for the restoration of wild habitat, says Zoe Harris, study author and director of the Centre of Environment and Sustainability at the University of Surrey, which led the research. “But to viably compete with field farming, vertical farms must cut their energy use and rethink the materials they rely on,” Harris said. 

Harris et. al. “A Comparative LCA of Field Grown Lettuce Versus Vertically Farmed Lettuce.” Food and Energy Security. 2025.

Image: Lianoland Wimons, CC BY-SA 4.0 via Wikimedia Commons