The performance of traditional African vegetables in urban outdoor modular living wall systems for food security in Gauteng, South Africa

Abstract

Urban agriculture can potentially lower global carbon emissions and create climate-resilient livelihoods and food security. As part of this quest for sustainable development, living wall systems (LWSs) with traditional African vegetables (TAV) can provide biophilic value and ecosystem services. This research analyses the performance of outdoor modular LWSs with TAV to improve household food security in South African (SA) urban environments. The pragmatic study entails three integrated focus areas: the contribution of urban small-scale food production to household food security and interrelated SDGs, the performance of outdoor modular LWSs as edible green infrastructure, and the performance of TAV crops in modular LWSs for household food security. Data capturing involved a three-pronged mixed-method methodology. Local experts provided insight into local LWS typologies and TAV crops through questionnaires. The six-month experimental study of two selected LWSs and nine TAV crops included variables of minimum and maximum daily temperatures, relative humidity, precipitation, soil temperature, water content and electrical conductivity, leaf biomass yield and plant stress. The researcher monitored fresh and dry biomass yields with a calibrated laboratory balance as the first performance indicator. Plant stress, the second performance indicator, was measured by chlorophyll fluorescence analysis. Data were statistically analysed. The research guides the technical characteristics of outdoor modular LWSs as edible green infrastructure in SA urban environments for performance improvement. It contributes to the revival of neglected crops by identifying TAV species suitable for utilisation in LWSs to improve household food security. The results favour locally produced outdoor modular LWSs with limited, robust, lightweight, recycled components entailing uncomplicated assembly. The study identifies seven TAV species suitable for household food production in LWSs. These include Asystasia gangetica (creeping foxglove), Coleus amboinicus (Indian borage), Corchorus confusus (jute plant), Dicliptera clinopodia (pink ribbons), Mentha aquatica (water mint), Portulacaria afra prostrata (dwarf elephant’s food) and Vigna unguiculata (black-eyed pea). Coleus amboinicus (Indian borage) and Portulacaria afra prostrata (dwarf elephant’s food) produced statistically significantly higher yields than the other crops. Selected compact TAV crops tolerating sunny, dry conditions can contribute to household food production in SA cities with a monsoon-influenced humid subtropical (Cwa) Köppen-Geiger climate classification.