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Understanding Urban Agriculture – Part 3, Calculating the Food Production Potential of a City

It has been well said that we do not see things as they are, but as we are ourselves. Every man looks through the eyes of his prejudices, of his preconceived notions. Hence, it is the most difficult thing in the world to broaden a man so that he will realize truth as other men see it.

Samuel Silas Curry, 1891

What does it take to convince a person that something can be done, when in the world of their mind’s creation they’re convinced it can’t be?

With the rise of Urban Agriculture (UA) worldwide we’re seeing the restoration of localized agriculture. Something that has always been done in human communities is being done again as a backlash against what is our current anomalous state of being – living apart from our food in urban food deserts created intentionally by local governments.

In my previous articles on the subject, I discussed how urban agriculture is a growing phenomenon worldwide and research released by the United Nations estimates that approximately 800 million people worldwide engage in urban agriculture. The figures are quite significant.

The UN estimates that “72 percent of all urban households in Russia raise food, and 68 percent do so in Tanzania. Berlin has over 80,000 urban farmers, while in China the 14 largest cities produce 85 percent or more of their vegetables” (1)

Despite reality, we’re seeing UA critics express opinions suggesting that UA can’t be carried out in cities for a myriad of reasons.

The obstacles to urban agriculture, textbook style

The textbook arguments centre around three main barriers to the uptake and expansion of UA in cities – legislative, regulatory and resourcing barriers. A lot of effort and discussion on UA centres on convincing authorities and regulators to support urban food growing. This makes sense, after all, the biggest obstacles to UA are regulations, by-laws and an entrenched hostility from the landscape architecture profession, especially from those employed by local government to design public spaces.

The question about resources is usually secondary and often more of an academic concern. It is this concern that I wish to address, to those ‘experts’ who claim that UA won’t work for reasons of resource limitations.

The real world obstacles to urban agriculture, a better distinction

I prefer to classify the obstacles to UA into two different categories, the first being physical, pertaining to the availability of land, water and other critical resources. The second being cultural, arising from, and existing in the minds of people, independently of any physical world limitation and human mental activity.

The reason for this dichotomy is because we’re looking at two distinct type of problems with two completely different classes of solutions.

The first category – physical limitations, are an objective problem. They present themselves as engineering problems, the challenge being to find a solution to achieve a particular outcome given the physical constraints of a specific system.

The second category – cultural limitations, are wholly subjective problems, dealing with the cultural biases, prejudices and unsubstantiated opinions of people, as they exist within their minds and the fruits of their thinking. These limitations are addressed by changing the way people think, whether it’s legislators, authorities or academics.

Physical or cultural limitations? The curse of the mini-farm mentality

In the academic debates suggesting that UA can’t work in cities, I’ve often seen a major logical flaw that ensures that the resultant discussions are worthless.

You would expect academics to be objective, but that’s another flawed assumption, they’re subjective humans just like everyone else, and though they may aim for objectivity, everyone has mental ’blind spots’ which elude scrutiny.

If we take a more philosophical perspective of the discussions to analyse the logic and reasoning, we see sloppy logic of untested assumptions creeping in. There is always one unspoken, unquestioned assumption, and it’s the same one every time – that UA is just scaled down rural agriculture, and therefore has the same qualities, requirements, limitations, problems and outcomes.

Nothing could be further from the truth, UA is a qualitatively different approach to food production under a completely different set of growing conditions. We UA advocates aren’t looking to clear vast areas of space in cities and recreate the social and ecological disaster that is rural agribusiness on a smaller scale.

The problem with the ‘mini-farm mentality’ is that it’s essentially a straw man argument that creates and imaginary problem to battle. It mistakenly assumes an agricultural solution which is not a UA reality and claims that it can’t be done, based on supposed sound resource arguments. The logical flaw is assuming that UA is identical to rural agribusiness, the only difference being quantitative.

Agribusiness is about destroying the environment and communities, UA is not. No person in a community setting would knowingly and willingly poison and pollute the place where they and their families live and eat. Simple enlightened self-interest.

Ecologically sound and sustainable design systems such as Permaculture utilize whatever space and resources are available to create food systems that co-exist harmoniously with the community and with Nature. There is none of the typical dominate and control, clear-fell and poison mentality in UA.

Sustainable design and working with available resources

A key point in sustainable food production is being able to create a design solution using available resources and bridging the gaps not with more money, resources or energy, but with innovation, creativity and sound knowledge of ecological systems.

A permaculture style “function over form” design which does not compromise functionality and efficiency with the dictates of vain aesthetics is well suited for UA design. First and foremost, to address the growing issue of food security in cities, we need to solve a problem, growing enough food – sustainably.

One point that critics of UA tend to bring up often is aesthetics. My question is this. Have they seen edibles growing in public spaces in other countries where UA is the norm? Or are they opposing virtual realities of “messy UA” they have dreamed up in their own minds?

Either way, window dressing and fluff such as the tediously repeated aesthetic concerns about ‘tidiness’ of the landscape architecture profession can be considered after the fact if at all, as a lack of perspective and priority is clearly evident here.

That said, if we were to do a design site analysis of a city, we would need to work out what resources were available to work with. Before anything else, we’d need to identify which resources we need to grow food.

Site analysis of a city, determining resource availability

I’ve always wondered what potential resources are available in the city of Melbourne, Australia, where I live.

Melbourne, Australia

To a permaculture designer the act of observation never ceases, the trained eye instinctively spots unutilised resources, areas with potential for growing food, or potential solutions waiting to be had in the surrounding landscape when going about one’s daily activities!

In this case, we’re looking at a whole city. To grow food, we primarily need land and water. We also need people, the community to support any UA efforts.

A good way to determine our resource potential is by identifying how many houses we have to work with.

Looking at the Census Statistics 2011 – Greater Melbourne VIC, we find the following statistics:

• People – 3,999,982

• All private dwellings – 1,636,167

• Occupied private dwellings 1,430,665 (91.0%)

• Unoccupied private dwellings 141,506 (9.0%)

The occupied private dwellings are comprised of:

• Separate house 1,039,342 (72.6%)

• Semi-detached, row or terrace house, townhouse etc 165,486 (11.6%)

• Flat, unit or apartment 219,111 (15.3%)

• Other dwelling 6,159 (0.4%)

Houses have rooftops, and rooftops have the potential to harvest rainwater. Now we know how many possible rooftops we have to catch rainwater from!

We also need to know how big those rooftops are, but that might be difficult. Rooftops are the same size or larger than houses, so we can use house size instead. How big area houses in Australia – big and getting bigger according to recent figures:

“We’ve never lacked for space in this wide brown land. Maybe that’s why Australians choose to live in the world’s largest houses, with an average size of 243 square metres. And, despite cries of overcrowding in our cities, research shows Australian houses are actually getting bigger. According to some data we’re also leading the world in floor space per capita. In fact, the average size of a new Australian house increased from 162.2 square metres to 227.6 square metres between 1984 and 2003, that’s a jump of 40%. The average new Australian home is now 10% bigger than even its US equivalent.” (2)

That’s plenty of roof space, and we know from our Bureau of Meteorology statistics that the Melbourne mean annual rainfall is 650mm.

Let’s see what these figures tell us.

Rainwater Harvesting Potential

If we consider only occupied dwellings, and of those we use only the categories of ‘Separate house’ and ‘Semi-detached, row or terrace house, townhouse etc’ and exclude ‘Flat, unit or apartment and other dwellings’ we have a total of 1,039,342 + 165,486 = 1,204,828 residences in Melbourne.

If the average house size is 243 square metres, and underestimating by not making any allowances for roof size being bigger than occupiable house size, we have a total roof space of 1,204,828 x 243m² = 292,773,204m².

Considering that each mm of rainfall on a square metre of roof amounts to one litre, the total rainfall that can be captured annually from Melbourne rooftops alone (as a gross underestimate) is 292,773,204m² x 650mm = 190,302,582,600 litres, or well over 190 megalitres of water.

Growing Space Potential

Assuming that occupied residences specified above (with the same exclusion of high density housing) allocate a paltry two square metres to food production as a hypothetical example, we would have a total of 1,204,828 residences x 2m² = 2,409,656 m², or just over 602 acres of growing space.

This is where a lot of academics get it wrong with UA, we don’t need large centralised farms, as distributed systems are far more resilient as they don’t have a single point of failure. One acre is 4,000 square metres, and it makes no difference in UA if that’s one single plot or 4,000 little ones, it’s the same growing space for vegetable gardening.

Food Production Potential

If Australians can produce the same amount of food as US home gardeners (3) – an average yield of 1/2 pound of fresh produce per sq. ft. of garden area.

1lb= 0.4535923kg and 1ft²= 0.09290304m²

To convert this kg/m² (0.5 x 0.4535923kg)/0.09290304m² = 2.44 kg/m²

So, 1,204,828 residences with each allocating 2m² each to food growing can produce 2,409,656m² x 2.44 kg/m² = 5,879,560kg or 5,880 metric tonnes of food.

Since nothing other than money talks for some people, if US home gardeners are achieving a $600 estimated dollar return for a 600 sq. ft. food garden, that’s US$1/ft², which translates to 1/0.09290304 = US$10.76/m².

If we calculate total value of produce, 1,204,828 residences with each allocating 2m² each to food growing can produce 2,409,656m² x US$10.76/m² = US$25,927,898, that’s almost US$26 million from 2m² of garden per residence.

Now, no reasonable person will claim that’s insignificant. If any critics still wish to maintain their position, I will gladly accept an insignificant donation of US$26 million into my bank account.

Let’s take it up a level now, beyond a paltry 2m² per household.

What would happen if our food gardens were the same size those of US gardeners – 600ft² or 55.741824m²? Total growing space becomes 1,204,828 residences x 55.741824m² = 67,159,310m² or 16,789 acres.

This will produce 67,159,310m² x 2.44 kg/m² 163,868,716kg or 163,870 metric tonnes of food which would be worth 67,159,310m² x US$10.76/m² = US$722,634,175 or roughly US$723 million which by today’s exchange rate is roughly US$723 million/0.75 = AU$963 million!

Since agriculture in Australia produces around AU$6,000 million, with the hypothetical figures of 2m² per household the city of Melbourne, Victoria could produce an additional 4.33% of the total Australian national combined peri-urban and rural produce value. If we push the figures and imagine all those households in the city of Melbourne with an average 56m² garden to match their real US counterparts, they could theoretically produce an additional 16.05% of the total Australian national rural produce value!

Now let’s not forget that the total Australian agriculture figures of AU$6,000 million include both peri-urban and rural figures, and peri-urban agriculture is usually about four times as productive as rural agriculture for the same space. Now we have a fairer comparison, which would suggest that urban agriculture figures would constitute a higher percentage of additional produce against the rural yield and monetary figures.

For those who have eyes to see

When we let go of any fixation with rural agriculture models, which are wholly inappropriate in UA applications, and think outside the square, it puts us in a better position to utilize the space and rainfall that is already available in a decentralized and distributed manner across the urban landscape to grow food in cities.

UA takes well thought out, intelligent design to work with the existing elements in a landscape, as is the practice in permaculture design. The idea of requiring clear-felled ‘blank canvasses’ is neither practical nor desirable, it’s in fact indicative of a lack of any real ecological/sustainable design skills.

Using real world data for calculations rather than speculation allows us to make more meaningful evidence-based assessments of the potential for cities to grow their own food. In this assessment, we see that the Australian coastal city of Melbourne has the potential to generate a significant quantity of food to address future food security issues.

One of the most significant conclusions that emerge from assessing the UA food production potential of a city is that the biggest obstacles to UA are not physical resource limitations, as some academics would have us believe. The biggest barriers to UA are cultural limitation, obstacles of the human mind, coming from those who choose think small, engaging in limited thinking and occupying themselves with short-term concerns, lacking the necessary foresight to consider the long-term implications of our current trajectory.


1. Urban Environment Food publication – United Nations,

2. “Why are our houses getting bigger?” Emma Sorensen,

3. “The Impact of Home and Community Gardening In America” report, page 12 – Amount of Food Grown and the Gross Domestic Garden Product


  1. You don’t understand the literature. The main obstacle to the sort of urban food production you envisage is economics, and the environmental cost. Please redo your calculations and include what each of those kg’s of food cost to grow, as well as the energy they provide when consumed (I mean, it’s easy to grow 25kg of potatoes; 25 kg of lettuce, not so much). Additionally, include the environmental costs of every home owner taking just 2 two trips a year (!) to Bunnings to buy a new shovel or whatever.

    On top of that, the suggestion that the average yield of the average homeowner would be even comparable to those of people who garden as a hobby and hence are intrinsically motivated is laughable.

    Finally, yes 26 million is a pittance. We’re talking about 4 million people here. $7 per person. That would mean that those people would be better off working half an hour flipping burgers than going through the effort of learning about gardening, tending to it, and year after year growing it; not even counting the cost of equipment, seed etc. Even your wildly optimistic high end comes down to $250 a year. Who wants to take a small part-time job (2 hours a week on average?) for $250 a year? Urban farming is fine as a hobby, but those advocating it as a pathway to a sustainable future are delusional.

    (and yes I’m an academic in this field, and no I won’t provide my real name or contact details…)

      1. Dear “Web Team”,

        How is it off tangent? It’s exactly on the topic this article is about; my point are step by step refutations of literal claims made by the author.

        The video you linked to is a marketing fluff piece. There is no data in there that refutes anything I said, nor that supports the article at anything but the most abstract level (i.e., ‘urban farming is good and possible’. Words are cheap – show me the numbers.).

        Look, I’m not opposed to urban farming, I do it myself. What I’m saying is that advocating large-scale urban farming as a sustainable solution is naive at best, and actively detrimental at worst, by undermining efforts that stress actual benefits of urban gardening – increased ecosystem diversity, urban area carbon sequestration (although there it’s better to have other plants, but food is better than asphalt at least), etc etc. There is literature enough on those other benefits – significant food production isn’t one of them, but no need for me to rehash that whole thing here.

        Re: the Bunnings thing, you’re assuming that gardening trips would replace shopping trips, which they don’t. You still need to go shopping because there is lot you can’t grow but still need without going back to hunter-gatherer/living in caves lifestyles. Also, it was just one example of the many additional costs the author failed to address.

  2. I try to grow food in my back garden. I do not think that the deterents of weather, insects, disease and maintainance time should be underestimated. All can be lost in one short summer holiday. It is easier and less stressful to shop for most people, a vast change would be needed in the rich west.

  3. Ah, I love the smell of ethnocentrism in the morning John! Have you thought that many parts of the world don’t have first world food and resource waste and the accompanying retail monopolies that go along with it. The whole world is not solely comprised of the US, UK, Australia and parts of Europe. There are other ways to view life overall, other values, and other ways to live!

    As an academic I trust you know the meaning and implication of the term ‘unsustainability’. Borrowing from your children’s future and their children’s future to fund a wasteful lifestyle for this generation that disrespects Nature and the planet Earth is hardly sensible.

    Time to take a look at the big picture and how people have lived in harmony with the planet in the past and in other cultures, the western mindset that is selfish, disconnected from Nature, that considers everything profane and nothing sacred, respecting nothing but money, is not life affirming, thinking this way is signing western society’s death warrant.

    We all have a choice to make the effort to live more sustainably, to be part of the problem or part of the solution. In respect to your example, where do toxic pesticides in mass produced agricultural produce factor in?

    Check my references to agricultural chemical contamination in my other article

    Also, the point the article is illustrating is the potential for food grown in urban areas, and in case you missed the point, this production system works in conjunction with peri-urban and rural agriculture to create a more resilient system. Yes, weather, pests and diseases affect all agriculture, but with all three it’s more a more resilient system.

    If you think urban agriculture’s contribution is insignificant, then I’m guessing you’re academic field is not history. The governments of the war era which encouraged people to grow food in urban areas in their ‘victory gardens’ would most strongly disagree with you…

  4. Hi Angelo,
    great article, I’ve visited your garden before and can visualise the bounty that would come in the future if enough people in Melbourne became motivated to create such plenty.

    I think that, despite the misgivings of Mr. Academic John above, this future is going to materialise, not because people are doing basic cost-benefit spreadsheets of their lives, evaluating the worth of flipping burgers vs spending time in the garden, but because of burgeoning capitalist and ecological crises over the coming decades will be affecting us all here in the Melbourne bubble.

    As an historical example, in the Great Depression in the 1930s, most workers across the world that had access to garden space grew extensive vegetable gardens and canned their produce, not to speak of the ‘victory gardens’ in the wars.

    More and more people are going to be realising the worth of UA to improve their lives, until a significant fraction of the population is doing it, which could hit some kind of cultural threshold point and catalyse a stampede to take it up.

    Final point, I noticed an error in your numerical calculations discussing the amount of water harvesting from roofs.

    You wrote:
    ‘292,773,204m² x 650mm = 190,302,582,600 litres, or well over 190 megalitres of water’

    It’s actually 190 Gigalitres that would be availalbe from rooftops, 3 orders of magnitude above 190 megalitres. Giga = 10^9 Litres. 1Mega = 10^6 Litres.

    1. Thanks for your comments James, you raise some excellent pointe there. Sometimes the bubble has to burst before people awaken from their consumerist hypnotic daze and cyclical routine.

      Yes, I stand corrected in the gross underestimate in my water figures by mistakenly calling a gigalitre figure a megalitre one. It should have been obvious as a megalitres figure would be way too little, but I missed that, so thanks for picking it up.

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