The benefits of roof gardening

For most citizens in affluent countries, the availability of food is usually taken for granted. Yet how secure is it in reality? Increasing numbers of people are concerned that unless agricultural practices move away from their present fossil fuel dependency, the future graph for food production will closely mirror the downslope of oil extraction. This pressing issue is being tackled by many inventive strategies to bring green and sustainable agriculture into the urban environment.

Under current projections, the world’s population is expected to climb from 6.8 billion today to 8 billion by 2025. At the same time, the total area of agricultural land is shrinking because of a range of factors including desertification, climate change, soil erosion, and development projects. Yields are also under threat from unpredictable weather, including droughts.

As the world comes to grips with the looming food supply issue, the old pattern of steadily sacrificing farmland for houses, industrial estates and golf courses is under increasing challenge. In the Seychelles, a hotel development was recently vetoed because it was earmarked for prime agricultural land.

It’s becoming obvious that to match food supply with population numbers, we need to find out-of-the-box sustainability solutions. Until we learn how to intensively farm arid areas and deserts, the extent of rural cultivable land can only be increased at the expense of forest cover, and this would significantly push up carbon emissions at a time when we can least afford it. Dubious technological fixes such as genetic modification and nanotechnology are not the answer. Sizeable efficiency gains can, however, be achieved through organic growing, sustainable, more intensive small-sized farms, and polyculture techniques.

National food insecurity can be roughly measured by the percentage of food a country imports. In Arab Gulf states, such as Qatar and the United Arab Emirates, this is as high as 90 per cent. Among developed nations, Japan imports approximately 60 per cent of its food, the result of a large population and relatively small landmass.

In a trend that suggests the way of the future, some low-food-security countries have been negotiating over the purchase or lease of land in other nations to ensure their own nutritional needs are met. Qatar is talking to Kenya about the Tana Delta region, a project that has experienced a backlash in this African country where widespread hunger remains a risk. Bahrain is currently eyeing rice farmland in the Philippines.

Another dimension to food availability is its affordability to the poor. A couple of years ago, food commodity prices shot up, precipitating riots in dozens of less developed countries. Food inflation has since been reined in, but there’s no guarantee we won’t see further hikes.

Is urban food part of the solution?

A sizeable chunk of a city’s greenhouse emissions is linked to the food items it consumes. High food miles associated with long transport distances have been acknowledged as a significant component of food products’ associated emissions. Other factors being equal, it makes sense to buy food grown close to home as a means of reducing one’s carbon footprint and supporting green and sustainable living.

Just a few years ago, we reached a pivotal point where for the first time in history more than half of the world’s population now lives in cities. With an accelerating trend towards urbanisation, it has been estimated that by 2050 about 80 per cent of people will be city dwellers. Until now, farming has been regarded as essentially a rural activity. More recently, there has been a noticeable sea change in favour of bringing food production into population centres, despite the obvious space challenges.

Fortunately, in recent years, a range of food growing options suited to urban areas has been developed. The most sophisticated of these are designed as self-sufficient “food ecosystems” whereby inputs and wastes are reduced to close to zero. Such systems may have the capacity to slash carbon emissions from the growing process and shrink transport-related fossil fuel use, while bypassing many of the challenges associated with modern farming.

City farms and community gardens

When people try to picture what food growing in a city might look like, the community Garden often comes to mind. The first of these appeared in Australia in 1977 as a kind of urban response to the self-sufficiency movement of the 1970s. From the Melbourne suburb of Nunawading, community gardens spread into other major cities and continue to multiply today.

Benefits of shared food plots extend beyond improved nutrition for locals. In difficult economic times, they relieve poverty by helping budgets to stretch further. Residents get to learn about food plants and how to grow them, while a stronger sense of community is created. Inner-city gardens provide a welcome green relief from hard urban aesthetics. Some larger city farm projects collect tonnages of organic waste from places such as restaurants, preventing them from going to landfill where they would generate methane emissions.

The unlovely inner suburbs of South-East London are home to a new guerrilla gardening movement whose members emerge at night to target unused green spaces such as grass verges and roundabouts. The following morning, passing commuters are greeted by a new bed of mature plants, some edible, others chosen for their beautiful flowers. In Australia, guerrilla gardening outbreaks have recently occurred in Northcote (Melbourne) and Redfern (Sydney).

In Detroit, in the US, urban decay on a vast scale has resulted in a patchwork city of communities and commercial districts, and vacant spaces where whole blocks have been demolished. Among the 7000 or so empty hectares, 500 gardens have already been established and many more lots could be allocated to food production, creating an interesting urban-rural mosaic. These projects are helping to feed the poor and cut crime statistics.

Another obvious step is the planting of fruit trees in parks and along residential streets as an alternative to non-productive ornamental species. In the US, this has given rise to a thriving urban fruit gleaning movement in several cities.

Boris Johnson, the Mayor of London, recently announced big plans to boost food-growing in the British capital, with the intention of creating 2012 new growing plots by the year 2012. The green spaces along canals and waterways running through the capital are receiving special attention. Another London initiative run by the group What If Projects involves the use of deep “grow bags” on land behind housing estates. These have been used to cultivate vegetables, salads and fruit.

Probably the most dramatic example of sustainable urban gardening is Cuba, which following the break-up of the Soviet Union in 1990 saw its oil imports halved and experienced an 80 per cent drop in food imports. During this crisis, the daily calorie intake per person initially fell by one-third before the country embarked on a major agricultural revolution. Chemical-intensive export crops such as sugar, citrus and tobacco were replaced with organic cultivation for domestic consumption. Population centres became filled with gardens running on permaculture principles and, today, Havana supplies half of its own vegetables. (See WellBeing issue 109 for a full report on the Cuban solution.)

Rooftop opportunities

Around the world, it’s becoming increasingly common to see flat or gently sloping roofs covered with a layer of green turf or wild grasses. In Germany, 10 per cent of all roofs have been greened in this way. Green roofs offer a wide range of benefits including:

  • Extension of the lifetime of the roof, which is protected from ultraviolet rays and temperature extremes.
  • Mitigation of the urban heat island effect, whereby cities warm up faster than their surroundings.
  • Strong insulation properties that reduce the need for both heating and air-conditioning.
  • Minimisation of stormwater runoff.
  • Increased biodiversity in inner cities.
  • Protection from pests and diseases due to the elevated position.
  • Aesthetic and therapeutic benefits for high-rise residents and workers who look down on these roofs.

Alongside the elevated lawns are other rooftop projects that involve food cultivation, and these have been trialled in such countries as the US, Egypt, India, Haiti and Cuba.

On the small scale, planters or polystyrene boxes can be used. Larger roof installations usually use lightweight hydroponic growing media such as vermiculite and zeolite. The roof needs to be capable of supporting the extra weight and may require strengthening. A thick plastic membrane prevents water from causing damage below, and if small trees are involved, this barrier incorporates root-proofing.

Some enterprising cafés and restaurants, such as Uncommon Ground in Chicago, are growing some of their ingredients on the roof above. Far more ambitious is a new American business called Sky Vegetables, whose plans to build and operate rooftop greenhouse gardens on supermarket rooftops are attracting great interest.

At the other extreme, in the basement of a 27-storey building in Tokyo’s CBD, a former bank vault has been transformed into a thousand-square-metre farm known as Pasona O2. This uses hydroponic techniques to grow a range of crops including tomatoes, lettuce and rice, and supplies a few restaurants in the building.

Living walls

Vertical gardens, also known as living walls, were developed a few years ago by the French botanist Patrick Blanc, who has installed them throughout the world in hotels, restaurants, museums and other public buildings. In an urban environment, they are an ideal space-saver that provides similar benefits to green roofs. Aesthetics of drab and ugly surfaces are improved, the air is filtered and runoff is captured.

Although most of these wall gardens are created for decorative effect, in the US a company called Green Living Technologies produces bases for vertical food gardens using adjustable aluminium panels. Each section of wall measures about two metres high and 10 metres in length and contains about 4000 dirt-filled cells that hold plants. These are irrigated from above through drip lines, and water is drained from the underside of each cell.

Urban Farming has been involved in a project in Los Angeles that sees the installation of these gardens in public spaces, where they can be used to feed the homeless and people on low incomes. According to project manager Joyce Lewis, bees and butterflies arrived within seconds of the walls initially going up.

Skyscraper farms

The concept of the vertical farm was originated by Professor Dickson Despommier of Columbia University. Unlike most other urban food models, this idea potentially has far-reaching ramifications and has aroused controversy in some quarters.

These multi-storey “farmscrapers” are self-contained ecosystems using hydroponic growing methods that reduce water demand, making them useful for arid countries. However, hydroponic systems do require the addition of a large range of trace minerals to the mix in order to protect the long-term health of eaters. Carbon extracted from animal wastes could be burned to create power.

Viewed positively, such closed loop structures could avoid the environmental damage caused by current farming practices. Pesticides and fertilisers are not needed, there is no soil to erode and there are no more worries about drought predictions. According to Gene Giacomelli of the University of Arizona, indoor farming requires at least 4–6 times less land area than the outdoor variety.

However, Jim Thomas of the international ETC (Erosion, Technology and Concentration) Group, is worried about Despommier’s view of vertical farms as a substitute for traditional agriculture rather than a complement to it. Thomas has concerns that this radical vision would drive the poor off the land to possibly make way for corporate interests. Under Despommier’s model, we might wonder what the countryside of the future would look like.

The Rotterdam plan

In 2001, a six-storey farmscraper development called Delta Park was proposed for Rotterdam. This location, despite its urban proximity, was largely chosen because of its closeness to the port, facilitating access to an export market. The vast scale of the design (one kilometre by 400 metres) and a perception that the vertical farm was too “industrial” led to its rejection.

In addition to vast numbers of pigs and chickens, Delta Park would have featured vegetable greenhouses on the roof, fish-breeding tanks in the basement and mushrooms and chicory in areas with no sunlight access. All the power would have come from renewable energy. However, Thomas Cierpka of the International Federation of Organic Agricultural Movements was unconvinced. For him, Delta Park cannot be described as “ecological” because of its disconnection from nature.

At this stage, the vertical farm remains a concept and there is no way of knowing for sure whether it will work as promised. Despite this uncertainty, interest in Despommier’s farmscrapers has been expressed by the cities of New York and Shanghai and by authorities in Jordan.

Backyard aquaponics

In aquaculture projects, there tends to be a build-up of fish wastes that can pollute the environment, while hydroponic chemical nutrients are liable to build up in the water and create a toxic condition.

Aquaponics involves the blending together of both techniques in an integrated closed-loop system involving fish and plants, where nutrients from fish manure fertilise the hydroponically grown plants, which in turn filter the water. Aquaponics is remarkable for being the most water-efficient agricultural technique currently in use, requiring about one-tenth of the water required for ground-grown vegetables.

All types of vegetables can be grown, except for root crops that require a greater soil depth. Tilapia is the most ideal fish species, as it is tolerant of variations in water conditions such as pH and temperature.

This agricultural model has arrived on the scene only in the past couple of years, but has been quickly adopted in Australia. It’s ideal for cities, being suited to walls and rooftops, and can be scaled up or down depending on land availability. Backyard-sized systems are likely to feature a fish tank and a few gravel beds for vegetable cultivation.

Initiatives in New Zealand

Although New Zealand is far from being a trendsetter in the urban agriculture field, there are city farms in several of the larger population centres. One of the best-known of these is the ReSource project in Manukau City on the edge of Auckland. Members of the Beachlands and Maraetai communities come here to drop off food scraps that are fed to worms, and grass clippings that are turned into garden beds.

In the central Auckland suburb of Herne Bay, the Kelmarna Organic City Farm was set up 25 years ago. In addition to growing a wide range of food species, it also fills a role as an educational centre and offers a work-skills program for people interested in gaining employment.

The Transition Towns movement is active in New Zealand, with seven participating communities and a national website. As the network expands, urban food production is likely to become an important area of focus.

Martin Oliver is a writer and researcher based in Lismore (Northern NSW).

Martin Oliver

Martin Oliver

Martin Oliver writes for several Australian holistic publications including WellBeing on a range of topics, including environmental issues. He believes that the world is going through a major transition and he is keen to help birth a peaceful, cooperative and sustainable reality.

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