In the United Kingdom, approximately 16,000 km2 of land is designated as urban7, of which green infrastructure constitutes approximately 50% (refs. 8,9,10) (an area 5.3 times larger than that used nationally for the commercial production of fruits and vegetables11). To understand the extent to which UH can make use of this apparent land resource, we used high-spatial-resolution datasets (specifically Ordnance Survey MasterMap and Google Earth Imagery) in a GIS to analyse the current and potential productive space for UH for the UK city of Sheffield. With 582,500 inhabitants12, Sheffield has the sixth largest population in England and Wales13. As is typical of larger urban areas, it is among the most deprived 25% of local authorities in the country14, indicating that considerable levels of food insecurity are likely15. Sheffield (as defined by the local authority boundary) covers an area of 36,800 ha, of which 22,700 ha are urban or peri-urban, comprising green and grey infrastructure — the focus of this study. Green infrastructure, including all green space within the city, covers 10,600 ha (45%; Fig. 1a), similar to other UK cities8,9,10. Urban allotments (that is, rented plots used specifically for horticultural production by individuals or households) are, in terms of area, one of the main resources for UH in Europe, with legal requirements in the United Kingdom and some other European countries for local authorities to provide allotment land16. Allotment land in Sheffield comprises 1.3% of green infrastructure, with a further 38% as domestic gardens (Fig. 1b). These areas of land are either in use or, in the case of domestic gardens, have the immediate potential to be managed by individuals for SBH. We used a set of spatial restriction criteria in a GIS (for detail see McHugh et al.17 and Grafius et al.18) to identify parcels of land within the wider green infrastructure of the city potentially suitable, but not currently used, for SBH. These parcels of land were split into community garden spaces, representing smaller land parcels where communities have open access to land for UH (parcel sizes range from 600 to 2,999 m2) and allotment spaces, which are larger patches of land composed of groups of allotment plots (250 m2 average size) rented to an individual or household16 (parcel size>3,000 m2). We thereby identified an additional 1,192 ha (11%) of green infrastructure that is potentially suitable for allotment-style growing (Fig. 1b) and 404 ha (4%) for community garden-style growing (Fig. 1b). Together, this represents 98 m2 per person in Sheffield: 71 m2 in domestic gardens and allotments and 27 m2 in the wider green infrastructure. This is an upper estimate, given that not all identified land would be usable in practice, and cultivation of smaller parcels (such as domestic gardens) may be subject to disproportionate losses to infrastructure (access, storage). Yet, effective utilization of less than one-quarter of this area would equal the 23 m2 per capita11 nationally used for UK commercial horticultural production of fruits and vegetables.

Fig. 1: The city of Sheffield. a, Current land-use within the local authority boundary. b, Current land available and green infrastructure suitable for UH. c, Grey infrastructure with flat roofs potentially suitable for UH within the city centre. Full size image

Recent developments in soil-free intensive CEH (such as hydroponics and aquaponics for high-value, high-yield crops) may facilitate the utilization of grey infrastructure within and on top of buildings. We investigated the potential area of flat roofs for UH, as they could allow year-round cultivation with minimal lighting requirements using greenhouses with rainwater harvesting for irrigation — although their areal extent is not well known. Green infrastructure is predominantly situated in the suburbs, yet the commercial city centre covers 229 ha with buildings comprising 58% of the area (Fig. 1c), while flat roofs cover 24% (32 ha) of this building area (Fig. 1c). As with expansion into green infrastructure, not all flat roofs would be useable for CEH in practice, so this value is a maximum. Although this area equates to just 0.5 m2 per person, the high-yielding nature of CEH production systems and focus on specific crop types could nonetheless contribute substantially to the city-wide UH potential19.

We therefore conclude that there is ample space in our case study city to expand UH, with 98 m2 per capita in green infrastructure augmented by small, but potentially highly productive, CEH space. This adds to the growing evidence that this important land resource could be made available for UH20,21,22,23 and that, at a global scale, urban land area would be more than sufficient to meet the vegetable demands of urban populations24.