Traditional African Vegetables: Living Walls

Rethinking food systems

Food systems that can provide a healthy diet for all are vital, with food security being one of the most pressing global issues,especially in Sub-Saharan Africa's marginal countries (FAO et al. 2018). The Covid-19 pandemic worsened the already inadequate progress in meeting the United Nations (UN) Agenda for Sustainable Development targets to end hunger, achieve food security and improved nutrition and promote sustainable agriculture globally (UN Statistics Division 2020). In addition to existing challenges of climate change, conflict and pests, the pandemic worsened the threat to food systems, with small-scale food producers affected the most (UN Statistics Division 2020). Food systems that provide affordable,safe and nutritious food without negative environmental impacts are thus required,with small-scale, sustainable edible living walls as a potential solution(Botes and Breed 2021).

Risks and challenges in food security and agriculture are exacerbated by the impact of climate change on the frequency and severity of natural disasters (UN Statistics Division 2020). Global temperatures are predicted to increase up to 3.2°C by 2100, with 2010 to 2019 recorded as the warmest decade leading to worldwide hurricanes, wildfires, droughts and floods(UN Statistics Division 2020). The impact of climate extremes on Africa is especially important, considering urbanisation projections and the impact on the agricultural sector (Botes and Breed, 2021; Davis-Reddy and Vincent, 2017; Dosio,2017). Mitigation of heatwaves in cities due to the heat island effect (IPCC 2019)through greening, insulation and cooling strategies such as edible living walls is important (Botes and Breed 2021; Köhler 2008).

It is evident that current food systems are not efficient in addressing hunger and malnutrition, are not sustainable, and do not promote economic growth. The substantial negative toll of the Covid-19 pandemic in 2020 and 2021 on human health and well-being and the global economy led to a renewed focus on the need for sustainable food systems. Moreover, increased public awareness of the origin and quality of our food through the support of organisations such as the farm-to-fork (F2F) strategy and the slow food movement (Fontefrancesco 2018) exemplifies the need for sustainable food production and systems. The slow food movement promotes good, clean, and fair food systems (Petrini 2016) without negatively impacting the natural environment,with fair remuneration for producers, processors, and distributors(Fontefrancesco 2018).

This article aims to first highlight why food systems need to be transformed to localised production with local African crops, second to propose localised, small-scale outdoor living wall systems (LWSs) with traditional African vegetables (TAVs) to contribute toward food security and nutrition, sustainability and economic growth, and third to feature two recent landscape architecture projects with edible LWSs in Gauteng, South Africa, reflecting on the local potential they offer for urban food production.

Why Africa requires localised food production with local crops

Food production accounts for almost 25% of total GHG emissions, mainly due to energy-intensive production processes and the transport of food products (Lopez, Aguilar et al., 2019). Localised food production is necessary to reduce GHG emissions and address local access to food.

The primary source of income in Sub-Saharan Africa is small-scale rainfed farming (Hadebe, Modi et al., 2017). Seventy-three per cent of direct economic losses in 2020 were documented in the agricultural sector, with the most significant impact on Sub-Saharan Africa's small-scale farmers due to the economic impact of the pandemic and climate extremes associated with global warming (UN Statistics Division 2020).Urban agriculture (UA), as a response strategy to the increase in food demands owing to the growing world population, can potentially contribute to self-sufficiency and employment opportunities (Eigenbrod and Gruda 2015; De Bon, Parrotet al. 2010). Implementing small-scale, low technology UA projects with vegetables would enhance these opportunities.

However,the limited diversity in global food systems, which incorporate only thirty mainstream crops that cannot tolerate the harsh climate conditions of Sub-Saharan Africa, makes this food system vulnerable to increased weather extremes due to climate change(Botes and Breed, 2021; Mabhaudhi et. al. 2019). Diversification of food sources is necessary for sustainable food security (Cheng, Mayes et al. 2017).

Improving the efficiency,economic feasibility and sustainability of food systems in Africa

With predicted urbanisation of 90% by 2050 in Africa(Gregory, Mayes et al. 2019), cities need to be optimised for UA purposes to supplement conventional rural agriculture (Eigenbrod and Gruda 2015). Food systems need to adapt to provide improved nutrition, more effective use of natural resources and increased resilience of production systems (Gordon, Bignet et al., 2017). Urban environments, especially low-income areas, offer many convenience and fast-food stores, with less access to healthy, nutritious foods such as affordable fresh produce, leading to nutrition-related health problems(Besthorn 2013). The excessive cost of urban land and pollution impact UA(Eigenbrod and Gruda 2015), although the integration of UA into urban planning is key to preventing risks of trace metals, especially leafy vegetables (Eigenbrodand Gruda 2015; Säumel, Kotsyuk et al. 2012,).

UA can improve access,availability and quality of food. When combined with rural agriculture and indoor farms, it could contribute significantly to addressing food security,which will become more critical in response to urban pollution and weather extremes due to climate change (Eigenbrod and Gruda 2015).

Key criteria for economically feasible and sustainable LWSs

Living walls refer to vertical growing platforms, normally part of the façade of a building(Köhler 2008), and for this article, refer to outdoor modular living wall systems, either integrated with a building exterior or free-standing. The high inset costs and maintenance requirements of LWSs impact their economic feasibility and sustainability (Perini and Rosasco 2013; Ottelé, Perini, Fraaij, Haas and Raiteri 2011). Also, the environmental resilience of LWSs,which entails a restricted planting palette to survive the stresses of an urban environment with specific soil, light and water requirements, poses challenges to the feasibility of LWSs (Botes and Breed, 2021). Innovations to increase the economic feasibility and resilience of LWSs include the use of cost-effective, context-specific,locally produced systems involving unsophisticated technology and the use of suitable plants (Botes and Breed 2021). Several studies agree that another way to increase economic feasibility is by introducing edible crops (Mårtensson, Fransson et al., 2016, Russo, Escobedo et al., 2017, Ling and Chiang, 2018). Edible crops can also increase food security and malnutrition whilst supporting the good, clean and fair principles of the slow food movement and F2F strategy.

The benefits of living walls as a UA component include not only a reduction in transport emissions, energy and water usage and organic waste but also mitigation of the urban heat island effect, carbon sequestration, oxygen provision, food security, nutrition and poverty (Zaid, Perisamy et al. 2018; Price, Jones et. al. 2015; Specht, Siebert, Hartmann, Freisinger, Sawicka, Werner et al. 2014).

Incorporating TAVs in outdoor LWSs

Towns and Shackleton (2019: 471) define TAVs as;"plant species that are indigenous and naturalised to Africa, well adaptedto, or selected for local conditions, whose plant parts are used as avegetable, and whose modes of cultivation, collection, preparation, andconsumption are deeply embedded in local cuisine, culture, folklore, andlanguage." Advantages of TAVs in comparison with exotic vegetables includetheir high nutritional value, tolerance to local climate conditions, shortgrowing season, low irrigation and agrochemical maintenance requirements (Araya2014), and their pathogen resistance (Botes and Breed 2021; Aworh 2018). TAVs cancontribute to achieving sustainable and resilient small-scale agriculture andfood systems in Sub-Saharan Africa (Botes and Breed, 2021; Mabhaudhi et al.,2019). Moreover, incorporating TAVs in UA through living walls could increase itseconomic feasibility and resilience.

Case studies

Two recently constructed edible living wall projects in Gauteng, South Africa, were selected as case studies for this article. The Playground market greening project,previously known as the Neighbourgoods Market, and the African crops LWSs on the Future Africa campus comprise living wall projects with vegetables and herbs.

The Playground Market, Juta Street (Braamfontein, Johannesburg, South Africa)

The Playground Market greening strategy (Figure 1) entails three overhead structures with two edible living walls providing herbs for utilisation at the weekly food market, as a retrofit to the multi-storey building, on the western façade of the second floor (Botes and Breed 2021). The project in Braamfontein, a central corporate suburb in Johannesburg, was implemented in March 2020. The landscape architects aimed to provide a green backdrop to the pop-up stands as an advertisement for the Strongbow brand and greening for the vibrant semi-outdoor market held in the parking area of the building, with improved exposure from both the market and street levels (Botes and Breed 2021).

The landscape architect, Charldon Wilken from the Fieldworks Design Group, selected mostly indigenous, low-maintenance, water-wise, edible and aromatic herbs with aesthetic characteristics for the living walls (Botes and Breed 2021). The two living walls are 5.4 m², each with five planted galvanised steel gutters fixed to a steel frame and clad with linseed treated timber slats, bolted onto the square steel tubing frames (Botes and Breed 2021; Wilken 2020: personal communication). The automated drip irrigation system installed at the top gutter of each LWS gravitates water to the lower troughs. Each channel has staggered drainage holes spaced 500 mm apart and set to run for thirty minutes three times a week (Botes and Breed 2021; Wilken, 2020: personal communication). The harsh microclimate condition on the western façade was mitigated by adding hydrogel crystals to the potting soil and vermiculite mixture as a moisture retention agent. And secondly, by designing the support structure with mesh and climbers as an overhead plane (Botes and Breed, 2021; Wilken, 2020: personal communication).

The plant palette (see Figure 2) contains species that can tolerate limited soil conditions, the harsh microclimate of the western façade, and heat generation from surroundings (Botes and Breed 2021). Edible plants specified include forest num-num (Carissa bispinosa)for their ripe berries tasting like cranberries and porkbush (Portulacaria afra) for its edible leaves with a zesty, acid taste. Wild rosemary (Eriocephalusafricanus), wild mint (Menthalongifolia), sweet basil (Ocimumbasilicum) and pelargonium species (Pelargoniumgraveolens and Pelargoniumodoratissimum) were included for their scented leaves, which can also be used as a garnish and added to drinks (Botes and Breed 2021; Wilken 2020:personal communication). The system's resilience is evident by the limited loss of roughly 10% to 15% of the plants following the two-month COVID-19 lockdown period,which affected the three-month post-completion maintenance period (Botes and Breed 2021).

African crops LWSs at Future Africa Campus, University of Pretoria (Hillcrest, Pretoria,South Africa)

The project comprises two exterior LWSs, each 6m2 in extent, at the Future Africa campus, which entails an innovative, multi-disciplinary research institute of the University of Pretoria, constructed in October 2020. The campus's urban setting and creative nature made this the ideal project to conduct innovative research as part of a PhD study in Landscape Architecture. The research aims to assess whether the utilisation of TAVs in local modular LWSs can be beneficial for food production in South African urban environments.

The living walls, positioned on the northern façade of the campus restaurant kitchen yard,comprise two living wall typologies. Both LWSs are manufactured in South Africa, with the Vicinity being a more sophisticated system and the Eco Greenwall a low technology system. The objectives of the research are to analyse and define technical characteristics of the modular living wall systems in South African urban environments, to develop a list of TAV species which has potential for vertical food production in South African exterior urban environments and to analyse the socio-economic feasibility of the two selected systems.

The Vicinity Wall (Figure 3) comprises hexagonal pots manufactured from recycled plastic, hooked onto aluminium strips fixed onto the kitchen yard wall. The pots contain reusable geotextile plant bags with three litres each for the growth medium and plants. Irrigation is a closed-loop dripper system, with water pumped from a tank system at the bottom of the LWS to the top planters. Water gravitates through drainage holes in the hexagonal planters to the bottom of the LWS. The irrigation runs for 60 minutes every alternative day in summer and twice a week in winter.

The Eco Green Wall (Figure 4), an unsophisticated technology, low-cost system, comprises an interlocking system of lightweight blocks, which are manufactured from are cycled polystyrene aggregate and cement mixture with seed trays. The seed trays have a capacity of 1,59 litres each for the growth medium and plants (Botes and Breed 2021; Van der Walt 2019: personal communication). The irrigation comprises a dripper line installed for each of the plant rows, which runs for 12 minutes daily in the growing season and for 8 minutes three times per week in winter. Advantages of the system include moisture retention, easy assembly and operation.

The plant list was selected for the research based on consultation with eight South African experts in the fields of edible and local crops. Following criteria such as nutrition value, commercial availability, heat, sun and frost tolerance and ornamental properties, the landscape architect selected nine leafy traditional African vegetables. These include Thunberg's pigweed (Amaranthus thunbergi), creeping foxglove (Asystasia gangetica), jute plant (Corchorus confuses), pink ribbons (Dicliptera clinopodia), water mint (Mentha aquatica), Indian borage (Plectranthus amboinicus), purslane (Portulaca oleracea), dwarf porkbush (Portulacaria affra prostrata) and black-eyed pea (Vigna unguiculata subsp. unguiculata).

The irrigation system links to the mainline of the Future Africa campus, which feeds from as torage dam with harvested water. Due to the failure of the primary irrigation pump system, there have been three irrigation interruptions ranging between three and four weeks since the installation. The failure resulted in a loss of only thirty per cent of the plants in both LWSs, demonstrating the resilience of both the systems and the planting palette. The Thunberg's pigweed, water mint, creeping foxglove, and pink ribbons were less tolerant of dry conditions and did not survive the dry spells. A second challenge entails the rock hyrax who consumed the purslane. Fencing the LWSs was used to mitigate the loss of plants. Plants,generally, seem resistant to pests and diseases, with grasshoppers observed regularly and mealybug occasionally.

Conclusion

Cost-effective, context-specific living wall systems containing local edible crops have the potential to contribute to sustainable food systems in Sub-Saharan African cities. Moreover, these systems provide environmental and socio-economic benefits that address food security,malnutrition, and the adverse effects of the urban heat island.

Living wall food systems involving unsophisticated technology can lower embodied costs,reduce energy and water consumption, and improve economic feasibility and resilience.

By incorporating TAVs into the plant palettes, LWSs also provide social,environmental and educational benefits. Notwithstanding these results, the research suggests that the LWSs and plant palettes need to be refined and that problems relating to the health risk of pollutants in urban areas must be further investigated.

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