ROOFTOP AGRICULTURE

HISTORY OF URBAN- AND ROOFTOP FARMING

Urban Farming

• 3100 BCE is the earliest record of food production within cities as home vegetable gardens were common in China. Besides providing food they also recycled households’ organic waste (Mandel, 2013). • Early latin american communities might also have practised urban agriculture for food security within cities (Mandel, 2013). • Throughout the developed world, urban populations have relied upon locally produced food until the Industrial Revolution of the late eighteenth and early nineteen centuries. The Industrial

Revolution changed everything for food production, factories and urban development took up the space in the city centre and agriculture moved out of the city to form rural ‘belts,’ which led to a demand for importing food into the city. Since the Industrial revolution, agriculture has periodically reentered cities, for instance during war for securing food supplies (Mandel, 2013). • Currently urban agriculture is beginning to be more popular as cities realise the benefits of local food production as cities are becoming more dense, expanding and multiplying in number (Mandel, 2013).

Rooftop Farming

• Rooftop agriculture likely dates back to 600BCE Babylon (present day Iraq) with the Hanging

Gardens of Babylon as the world’s first rooftop farming project with production of fruit, vegetables and maybe even fish (Mandel, 2013). • During the 16th century, the Aztecs were said to have built sophisticated rooftop farms that included waste management strategies (Mandel, 2013). • Today’s rooftop gardens and farms do more than address subsistence. They foster healthy eating, community building, stormwater management, business development and the occupation of underutilised space, thereby fulfilling multiple goals at the same time. The rooftop farms and gardens appear in various shapes and sizes, with production of a wide range of yield, and are diverse places intended for various purposes (Mandel, 2013).

INTRODUCTION

Rooftop agriculture is the cultivation of plants, animals and fungi on rooftops primarily for the purpose of human use and consumption. The products gained from such rooftops include many goods such as foodstuffs, fibres, animal products and medicinal plants (Mandel, 2013). Rooftop agriculture shouldn’t be seen as the one solution to cure all hunger or that it will dominate food production in all cities, but should be regarded as part of the greater urban food system. It is connected to community gardens, farmers’ markets, grocery stores and rural agriculture. As a key principle of ecology states, diversity in a system breeds resilience. This principle applies to food

systems where rooftop agriculture enhances the diversity, hence the resilience of the greater urban food system (Mandel, 2013). For people living in slum areas they will not for instance have much access to grocery stores, so rooftop agriculture can provide some food security. Productive green roofs do not only produce food but combine it with ecological sustainability, as for example reduced rainwater run-off, temperature benefits, biodiversity, improved aesthetic value and air quality (Dubbeling & Massonneau, 2012).

There is a blurry boundary between gardening and farming, and there is no clear definition. One definition states that gardening is the production of agricultural products for self-consumption, charity or gifting, and that farming is the production of these same goods in exchange for money (Mandel, 2013). In slum areas, products from an agricultural rooftop will function as a substitute to buying food or, depending on the scale, as an income generating activity. Rooftop agriculture can broadly speaking be divided into three categories and scales; rooftop gardening, rooftop farming and as the largest scale rooftop agricultural industry (Mandel, 2013). Rooftop farms and rooftop agricultural industries can be quite challenging and expensive to start up. Rooftop gardening, on the other hand, is for everybody and all levels of experience (Mandel, 2013).

There are three primary types or systems of food producing green roofs (also see Tabel 1): • Agricultural green roofs, or direct producing green roofs, where crops are grown directly into (shallow) beds in a soil-based growing medium, which is possibly placed on top of a waterproof membrane or additional layers as a root barrier, drainage layer and an irrigation system (Dubbeling & Massonneau, 2012). • Rooftop container gardens or modular green roofs where plants as vegetables are grown in pots, bottles, raised beds etc. that contain a soil-based growing medium. The containers can vary in shape and size and be made of local materials. The growing medium can be made up of mixtures of soil, compost or wood chips (Dubbeling & Massonneau, 2012). • Rooftop hydroponic systems where plants are grown using water based nutrient solutions instead of soil. On-going fertiliser inputs are necessary. They can be placed in an open-air setting or grown under cover (glass or plastic) to increase yield and extend the growing season (Dubbeling & Massonneau, 2012).

Rooftop gardens can be placed on many different buildings from individual homes to offices to community buildings (Dubbeling & Massonneau, 2012). Finding relevant litterature on rooftop agriculture in slum areas was challenging.

Direct producing green roof (Krummert, 2013) Rooftop container garden (Pinterest, 2022) Rooftop hydroponic system (Pinterest, 2022)

FOOD IN UGANDA

Food security is a serious issue for the poor and underprivileged in urban areas. With the population growth happening in combination with urbanisation in Uganda, a large pressure is put on rural farmers and ecosystems to increase yield and arable land. This, for instance, leads to an overly use of inorganic fertilisers and chemical pesticides that then leads to water pollution and soil degradation, which in the long term lower yield and increases the need of arable land. The consumers will also also be affected by the chemical pesticides, which leads to long-term negative health effects. Climate change and climate variability also affect agricultural supply from rural areas, which becomes less and less reliable. It has consequences for everybody, but especially for women, children and elderly in vulnerable situations. Lack of basic food and water is a frequent cause of domestic violence within deprived households, where it is often women and children suffering. With low-income communities in cities being very dependent on the market and market prices for vegetables, it leads to high expenditures or a low intake of fresh vegetables, which then causes nutritional deficiencies. Finally, organic waste from food waste makes up 90% of the waste in Kampala. 28,000 tons of waste is collected to landfills, and another 42,000 tons is illegally dumped elsewhere, which leads to significant methane emissions that accelerates climate change (Vertical and Micro Gardening, 2022).

CLIMATE CHANGE IMPACTS

In cities there are a high amount of paved and impermeable surfaces, which results in poor stormwater drainage as well as a higher temperature in cities. This phenomenon is known as the urban heat island effect caused by dark surfaces. Green roofs can potentially improve these problems and make cities more sustainable and viable. Further benefits of a green roof are that the lifetime of the roof might also be prolonged if the green roof is well designed and maintained. Inner-city biodiversity is promoted and if there is a production of food it addresses food security issues. However, it can be difficult to get some of the same impacts with a rooftop agricultural garden as with green roofs. On agricultural green roofs the cover of plants is often not continuous, particularly with seasonal crops. There are also additional demands for safety and access. It varies between the different types of rooftop garden systems how much impact they have. For instance, the hydroponic system doesn’t prevent water run-off because it has no soil (Dubbeling & Massonneau, 2012).

Urban Heat Island Effect

In order to reduce the urban heat island effect, a permanent soil/vegetation coverage on the roof should be maintained and generally more than 75% should be covered to provide any measurable effects. This is also the case for reducing stormwater run-off. Plants that are good for maintaining a permanent green cover are those with a high leaf surface area, perennial crops, self-seeding plants and fast growing plants. When reducing the urban heat island effect, energy is potentially also saved on cooling down the inside of the building. Green roofs can also function as insulation, preventing heat loss from the building (Dubbeling & Massonneau, 2012).

Carbon Storage and Carbon Sequestration

In regard to carbon storage, green roofs store less than urban forestry systems because of lower plant biomass, and for an agricultural green roof to store the same amount as a non-agricultural green roof the green coverage needs to be maintained throughout the whole year. As for carbon sequestration potential it is influenced by climate, soils, condition, plant species and the harvesting of vegetables on an agricultural green roof. During harvest a large part of the sequestered carbon by the vegetables is lost, making agricultural green roofs less effective in carbon sequestration than non-agricultural green roofs (Dubbeling & Massonneau, 2012).

Rainwater Run-off

There are three factors affecting the efficiency to reduce rainwater run-off: deeper soil retains more water, the bigger the planted surface area the more water is retained and a year-round coverage is more effective than seasonal coverage. The plants also impact efficiency, the best approach is using a high leaf surface area and a large roof mass. Seasonal crops are less efficient at times of year when the plants are absent or in the development stage. Therefore rainwater run-off can be reduced optimally through the choice of cultivation methods (Dubbeling & Massonneau, 2012).

Biodiversity

Green roofs can add to biodiversity with an increase in insect numbers and density, as the insects attract hungry birds. To get the biggest variety in insects and birds there should be a diverse choice of plants, diverse depth and composition of the growing medium and perennial plants flowering at different times of the year. In the container roof system some small containers can be used as ponds, attracting different types of water-loving insects (Dubbeling & Massonneau, 2012).

Air Pollution

Green roofs can improve air quality and reduce air pollution. Airborne particulate pollutants, heavy metals and volatile organic compounds are reduced by being deposited on the soil, on the leaf surfaces and onto the moist internal surfaces of the leaves. Plants also absorb greenhouse gases and release O2 through photosynthesis (Dubbeling & Massonneau, 2012).

Food Security

Food security will be improved by agricultural productive green roofs producing local fresh food. The roofs offer the possibility to grow food in inner city and densely populated/built spaces. By having the food grown and consumed in the neighbourhood it will also contribute to reducing greenhouse gas emissions caused by transport, cooling, storage, processing and packaging of the food (Dubbeling & Massonneau, 2012).

Green Infrastructure

Green roofs bring nature back into the city and densely built-up spaces which improves the living environment. Agricultural green roofs also offer opportunities for relaxation and physical exercise.

Depending on the thickness of the roof and the amount of vegetation cover, green roofs can act as noise buffers reflecting and absorbing part of the sound. Also, green roofs contribute to the green infrastructure of a city (green mosaic), connecting to other green areas in the city (Dubbeling & Massonneau, 2012).

Other Benefits

Agricultural green roofs also provide community involvement, educational value, healthy fresh food, aesthetic value, a connection to nature, economic value and create green jobs (Dubbeling & Massonneau, 2012).

TECHNICAL ASPECTS, DESIGN AND MANAGEMENT

Weight

Installation

Costs

Repair and Maintenance

Alteration and additions

Plants Direct Agricultural System/ Shallow Beds Modular System/ Container Gardens Hydroponic System

Heavier system that may require structural support, it depends on the depth of beds and what growing media is used Lighter system depending on the type and numbers of containers used, can be installed on an existing roof which

Installation of protective layers needed first to protect rooftop from direct contact with roots and growing system

Depends on what rooftop protection and structural support is needed

Layers need to be lifted during reperation which disturbs the vegetables have sufficient structural capacity and that slopes up to 15 degrees* Can vary a lot**

Quick installation and containers can be moved Generally requires higher investment and technical knowledge

Depends on the number and quality of containers, use of recycled materials can lower the cost The cost of fitting growing containers and structural support is generally high, the soluble fertiliser is also expensive

Containers can be moved easily A higher technical level is required for maintenance

Difficult to make alterations and a new installation takes a long time to implement Alterations and additions can be made easily Difficult to make alterations and a new installation takes a long time to implement

Root growth is limited by the depth of the beds Root growth is limited by container capacity, but even small trees can potentially grow in containers Vegetables that grow in water

*Weight range (kg/m2): 50-1000 **Weight range (kg/m2): 20+ Tabel 1: A comparison of direct/shallow beds, modular system/container gardens and hydroponic systems (Dubbeling & Massonneau, 2012)

Weight and Building

The weight of the materials is a concern when making a green roof. Therefore beds or containers are often quite shallow, so that lightweight material can be mixed with the soil. Many kinds of

fresh organic matter can be used for growing plants (e.g. wood chips) if sufficient compost is not available. It is then fertilised and covered with at least a thin covering of compost or soil. Almost any vegetable can grow in shallow beds, and the containers/beds function like a regular garden except they need to be watered more often (Dubbeling & Massonneau, 2012). The weight of an agricultural green roof is determined by the depth of the beds/containers, type of supports and what growing media is used. The growing media weighs more in a water-logged state, also crops, (rain)water storage and human presence add to the weight. Agricultural green roofs can be distinguished into intensive systems that have a soil depth between 15cm and 1m and extensive systems that have soil depth between 5cm and 15cm. When deciding what type of roof garden to install, it depends on the structural capacity of the roof, the cost of installation and what type of plants should be grown (see Tabel 2) (Dubbeling & Massonneau, 2012).

When adding a rooftop garden to an existing roof the most heavy parts should be located near columns and beams. Concrete buildings with a flat roof are in general the best suited buildings for a productive green roof, as they require less additional support than for example a steel frame. A maximum slope of between 3° and 10° is recommended, however the lower a slope on a flat roof the more of an effective drainage system is needed (Dubbeling & Massonneau, 2012).

If the rooftop garden is placed on a tall building it will be more exposed to winds, which can influence safety, access and water requirements. It also requires more energy to transport materials to the roof (Dubbeling & Massonneau, 2012).

Extensive System Intensive System

Weight

Lighter system because of shallower soil* A high structural capacity is needed due to more weight on the roof**

Might need additional or new structural supports

Because of load bearing demands it is more expensive

Because of the larger soil depth a high variety of species is possible and

Building

Can be used on existing roofs, a few additional supports may be required

Costs

Cheaper because none or only a few additional load bearing supporters are needed

Plants

Only crop species with more shallow roots as for example leafy greens and herbs it will be more efficient plant growth and healthier plants

*Weight range (kg/m2): 50-200 **Weight range (kg/m2): 200-1000 Tabel 2: Comparison of extensive and intensive systems (Dubbeling & Massonneau, 2012)

Climate, People and Basic Features

The local climate, such as exposure to sunlight, wind velocity and shading, influences the design and choice of plants (Dubbeling & Massonneau, 2012).

Since a rooftop garden is accessible for people, safety should also be taken into account. Safe access and movement is necessary and constructions as for example a fence might be necessary (Dubbeling & Massonneau, 2012).

Before constructing a rooftop garden information on regulations from the city should be obtained (Dubbeling & Massonneau, 2012).

Basic features as well as possibilities for and constraints of the site should be considered when designing a rooftop garden. These include: sun areas (and how much sun), access to water and electricity, interior and exterior access, circulation areas, railing, special features related to safety, etc. Also the cultivational and recreational uses of the garden should be considered, which include; food production, relaxation and contemplation, gatherings, storage, rainwater recovery, area for doing manual labour, drying of clothes and composting. The size of each function/area should be determined according to needs and priorities, and the design needs to be functional and inspiring (Dubbeling & Massonneau, 2012).

Growing Medium

The ideal rooftop bed or container should be around 23cm to 30cm deep. Such a depth encourages plenty of root growth and can support even tall plants like sweet corn. However they often need to be shallower due to weight. The biggest disadvantage of making them shallower is that they can store less water and therefore needs to be watered more frequently. Vines with large leaves can be challenging in shallow planting beds, but with sufficient volume (deeper bed or fewer plants) or more watering, it is possible to grow them and let them flow over a rooftop or down the side of a building. Root crops also require deeper beds (Dubbeling & Massonneau, 2012). The composition of the growing medium depends on weight considerations and on the different plants’ growing requirements for space and nutrients. Other growing media that are lightweight and easily obtained at little or no cost can be used to reduce the weight and therefore make it possible to have deeper planting beds. These include vermiculite (worm compost), woodchips, household compost, corncobs, rice hulls, shredded coconut husks, sugar cane bagasse (what is left after the juice is squeezed from the cane), coffee pulp etc. The growing medium should consist of sufficient organic matter and allow the roots to aerate sufficiently, it should be a blend of inorganic materials with organic materials. An example of an inorganic material could be cut open soda cans or pieces of coconut husks that are lightweight and therefore making it possible to have deeper planting beds while at the same time making the beds well-aerated (Dubbeling & Massonneau, 2012). Another good self-made growing medium is approximately 2cm-12cm layer of closely packed weeds covered with a bit of compost (Dubbeling & Massonneau, 2012).

Water is the growing medium in the hydroponic rooftop system. In general it weighs less than the soil-based system (Dubbeling & Massonneau, 2012).

Construction and Planting

Principles for construction: • Low cost (Dubbeling & Massonneau, 2012). • Use of recycled and locally available materials and growing media (Dubbeling & Massonneau, 2012). • As much as possible use of ecological production practices and avoided use of chemical fertilisers, herbicides and pesticides (Dubbeling & Massonneau, 2012). Pollution can be an issue and should be taken into consideration and minimised. There is a risk of urban soil being contaminated. Close to industrial areas there might be pollution in the air, the produce can be washed in a mixture of water and vinegar before consumption to reduce the risk (Dubbeling & Massonneau, 2012).

Construction Container Gardens

Many different types of containers can be used such as raised planting beds in wood, old tires, bags, pots, bottles, buckets etc. The size of the container determines what plants can grow in it. With a portable container it can be placed anywhere and moved if necessary, for example according to sun/ shade or wind. Container gardens are more safe for the condition of the roof since the roots are not in contact with the roof and it is even better if the containers are raised from the roof so that air can circulate underneath, keeping the roof surface dry (Dubbeling & Massonneau, 2012). A PVC can be added in the centre of the planting bed to see how much (if any) water is standing in the bottom and so judge when to water (Dubbeling & Massonneau, 2012). A PVC pipe with holes in it can also be used as an irrigation system, by putting it in the soil and pouring water into it for the plants to suck. A terracotta pipe can be used for the same purpose (Dreamtown, 2022). A water reservoir can be installed in the containers so that watering can be done less frequently. It is made with a water container placed in the growing container, a small amount of the growing medium is in permanent contact with the water reservoir. A perforated tube filled with potting soil is placed between the two containers and acts as a wick transporting water from the reservoir to the roots. An overflow hole separates the water reservoir from the growing mix, so that there is air to the roots (Dubbeling & Massonneau, 2012).

Choice of Plants

The factors that determine which plants to choose are: Local climate, placement on the roof, applied rooftop agriculture system, growing medium and food demand. However, there are also some general principles to follow when choosing plants, especially with a climate change perspective in mind (Dubbeling & Massonneau, 2012):

• Drought resistance or tolerating low water conditions, to limit use of water and adjusting to drier growing conditions (Dubbeling & Massonneau, 2012).

• Heat tolerance and wind resistance to adjust to growing conditions on a roof (Dubbeling &

Massonneau, 2012). • As indigineous and endemic as possible, such plants are often the best adapted to local climates while they also attract local populations of insects and birds (Dubbeling & Massonneau, 2012). • They should attract butterflies and insects to improve biodiversity and fertilisation. Selecting plants that grow and flower at different times of the year helps with providing food and habitat for the insects at all times (Dubbeling & Massonneau, 2012). • Grow plants from seeds collected locally. These plants are more suited to local conditions and therefore typically require less maintenance (watering, pest control etc.) and have a greater chance of survival. At the same time the carbon footprint is reduced with less transport while the genetic composition of the local species populations is maintained (Dubbeling & Massonneau, 2012). • Aesthetic pleasing with for example the use of a variety in plant mass, texture, colours and a choice of plants that grow and flower at different times (Dubbeling & Massonneau, 2012). • A wide diversity of plants. The greater the diversity the more different insects and birds are attracted. It also makes the roof more resilient with a better chance of year round plant cover if for example some species die under certain conditions others might survive. Furthermore, different plants also contribute to a healthy and varied diet and reduce risks of pests and diseases.

Medicinal plants and herbs can also be grown besides vegetables, and they are often suitable for growing in shallow beds (Dubbeling & Massonneau, 2012). • Plants potential to maximise carbon sequestration and capturing of particulate matter. Small tree species and non-food plants that ensure permanent cover increase the potential (Dubbeling &

Massonneau, 2012). • Growing intensively and providing as much permanent plant roof cover as possible. This increases impacts on rainwater run-off and the urban heat island effect, as well as reduction of air pollution, maximising food production and improving biodiversity etc. Food plants with high yield and little use of space are to be preferred. Dwarf varieties of plants might be a possibility (Dubbeling & Massonneau, 2012).

Less than 15cm of growing media Drought tolerant herbs, strawberries, leafy greens

Shallow beds and container gardens systems

15-30cm of growing media

30cm+ of growing media Above mentioned plants + chives, lavender, sunflowers, time, cilantro, lemongrass, sage, tomatoes

Above mentioned plants + kale, carrots, potatoes, blueberry bushes, raspberries, gooseberries, boysenberry or even small fruit trees

Hydroponic systems

Cucumbers, tomatoes, eggplants, peppers, leafy greens

Tabel 3: Examples of suitable plants for different rooftop garden systems (Dubbeling & Massonneau, 2012)

Production Techniques

Similar considerations are present with production techniques as with the choice of plants. These ‘climate smart’ production techniques are recommended (Dubbeling & Massonneau, 2012): • Use of as much as possible locally available and if possible recycled (waste) materials. The durability and origin of support structures shall be taken into account. Recycled materials can be used for edging and containers. Wood is often locally available at a low cost and is also a light material but needs to be replaced regularly. Aluminium or concrete lasts longer, but also has a larger carbon footprint and concrete can be very heavy (Dubbeling & Massonneau, 2012). • The practice of mulching and shading in order to reduce evapotranspiration and enhance moisture availability for the plants. Mulching is when you protect the soil by adding a layer of organic matter such as dead leaves, cocoa shells, wood chips, straw or cardboard (Dubbeling &

Massonneau, 2012). • Water early in the morning or late afternoon to reduce water loss (Dubbeling & Massonneau, 2012). • Hold on water longer by adding a water absorbing medium such as vermiculite in the growing medium (Dubbeling & Massonneau, 2012). • Larger plants should be planted along the edges to act as wind breakers and reduce the drying effect of the wind (Dubbeling & Massonneau, 2012). • Rainwater harvesting and use of kitchen water to reduce the use and avoid competition with drinking water. A combination of different water sources is the most sustainable. Water containing chemical detergents should not be used (Dubbeling & Massonneau, 2012). • Use of ‘low-space production techniques’ and an optimal use of vertical space to increase the plant production per square metre (Dubbeling & Massonneau, 2012). • Minimal use of external inputs and fertilisers. Instead use compost made from household waste, manure tea (a fertiliser made from animal manure and water) or other organic fertilisers. Use organic pesticides such as chilli or garlic or use insect traps (Dubbeling & Massonneau, 2012). • Maximise both food production and the potential for income generation. This will reduce vulnerability to food shortage/increased food prices and changes in income. To diversify the income sources enhances the resilience of the producers, and allows for further investments (Dubbeling & Massonneau, 2012).

Investment and Maintenance Cost

The cost of an agricultural green roof depends on the building expenses, planting related expenses, repairs, maintenance, organisation expenses and possibly teaching people in urban farming etc. The costs are offset against savings made by growing one’s own food, potential reduced cooling inside the building and other income generating activities such as eventual sales, teaching etc. (Dubbeling & Massonneau, 2012).