Urban Agriculture Research

Robert McDougall’s Urban Agriculture Research –

Plain English Summary

Chapter 1 – How productive are urban gardens?

This document summarises work undertaken by Robert McDougall, PhD student from the University of New England, on urban agriculture in Sydney and the Illawarra. It is intended to be a plain English summary of the first chapter of my thesis, which is being submitted for publication in a peer reviewed journal. Please feel free to share this document with any interested parties. If you would like more information, or a copy of the original chapter (which is a lot longer and contains a lot of statistical analysis) feel free to contact me at robert.n.mcdougall@gmail.com.

My remaining chapters cover the potential for upscaling urban agriculture in Sydney, the role that the surrounding environment plays in providing pollination services to urban agriculture and the role of natural enemy pest control, and I’ll write and distribute summaries similar to this on those chapters in the coming weeks and months.


One of the most pressing humanitarian and environmental challenges of the 21st century will be to feed a projected global population of 9 billion people. Land clearing and more intensive use of existing croplands are often considered to be the two main options to increase crop production, yet biodiversity loss and increased greenhouse gas emissions are associated with both of these approaches.

However urban environments are potentially an untapped resource when it comes to food production. Despite limited available land, cities have played a valuable role as agricultural areas at various times of crisis throughout the 20th century. Examples include during the world wars, when the ‘Victory Garden’ movement in the UK and USA saw cities produce around 10% of the total food supply for those countries, and in Cuba after the collapse of the Soviet Union.

I undertook this study to get an idea of how productive typical urban food gardens can be, and to determine the potential that cities have for producing more of their own food supply. Many permaculturists and other urban gardeners claim their gardens are highly productive – a claim backed up by the small amount of systematic research that has been carried out – but productivity by itself doesn’t paint a full picture. I wanted to get an idea of what inputs were required to achieve this productivity and how sustainable the gardens were, and as far as I’m aware my research is the first to really examine this in detail.


As I wanted data on typical urban gardens I crowd-sourced the information, seeking out volunteers willing to record their gardening practices over the course of a year. This was a big ask but in the end I had 13 excellent volunteers compile a year’s worth of records on what they harvested, how much work they did in their gardens and what materials they put into them. They worked in community gardens, their backyards and in market gardens throughout Sydney and the Illawarra. I also had another 15 gardeners who signed on to help at the beginning who weren’t able to finish the full year, but gave me some incredibly valuable information along the way.

The first thing I did was survey the gardeners on a whole range of topics like their experience with gardening and what motivated them to do it. I then gave them logbooks and scales to weigh their produce and left them be for a year while I worked on other aspects of my project. After the year was up I carried out a range of analyses on their data looking at the economics of the gardens and carrying out an “emergy” analysis. That’s not a typo in the word emergy – it’s a contraction of “embodied energy”, a type of analysis that examines substances and processes based on how much solar energy was ultimately required to create them or allow them to occur. As sunlight is what ultimately powers the earth, emergy analysis allows you to compare virtually anything to anything else – the ultimate “apples to oranges” comparison – and I thought it was a good way to account for the diverse values that urban gardens can have.


My results were something of an emotional roller  coaster.

MotivationsThe first results I got were those from the surveys I did with the gardeners, and what I found was that producing large quantities of food wasn’t a high priority. The chart on the right shows the average importance to gardeners, on a 1-5 scales, of the nine possible reasons I gave as to why they might be involved in gardening and as you can see, reducing food costs (a proxy measure for producing lots of food) was the least important of all the options.

As someone who wanted to research food production this was disappointing, but science is about finding the facts rather than getting the answer you want to hear, so I pushed on. However when I finalised the data at the end of the year I got a very pleasant surprise. Despite the gardeners not being motivated to grow large quantities of food, they ended up doing exactly that. The average output over the course of the year was 6.97 kg per m2. That number may not mean much on its own but the average output of commercial fruit and vegetable farms across Australia is just 3.38 km per m2 – people working in their yards and community gardens just for the fun of it are producing more than twice what commercial farmers are per unit of land. This is especially impressive when you consider that the majority of the gardeners I worked with had no formal horticultural training – most had been gardening for a long time (average of 21 years) but had picked up all their knowledge informally through this process.

This was a really exciting result, which fit with what many gardeners already suspected, but what did it take for them to achieve these outputs? This was the next big dip on my emotional roller coaster – it turned out, when I did the emergy analysis, that the investment of labour and materials per kilogram of produce harvested was very big, more than 10 times what is invested in commercial farms. So while the gardeners were making efficient use of land, it seemed they weren’t making very good use of labour and materials. And what’s more, an analysis of the sustainability of these inputs showed that, despite many gardeners saying they were highly motivated by environmental goals, the gardens were on average not all that sustainable. On a measure called the Environmental Loading Ratio (ELR) they had a rating of 6.37, which is generally considered to be ‘moderate’ impact (above 10 is high impact, below two is low), a figure close to the average for conventional commercial farms and probably not what sustainably minded gardeners were going for.

But the mood changed again after I changed my perspective a little. I realised I may have been thinking about the inputs into the gardens the wrong way, particularly in how I classed inputs as renewable or non-renewable. In emergy analysis the term ‘renewable’ is used a little differently to in general conversation. In this context it means something that’s availability is not affected by its use – rain is a good example of a renewable resource in this sense, as rain falls on a patch of land whether or not it nourishes plants or just falls on concrete and drains into the gutter.
In my analysis I had been treating labour as a mostly non-renewable resource as this is the way it would typically be treated in economics. If you ‘spend’ an hour of labour on an activity like gardening, this is a cost, as you can’t invest that hour in working and making money. But given that the gardeners who worked with me mostly thought of gardening as a recreational activity, I realised that this was perhaps the wrong approach. If gardeners weren’t able to garden they most likely weren’t going to spend that time working as it was their recreational time, they’d likely spend it on other recreational activities that didn’t produce anything (e.g. playing sport or video games). Thus gardening labour is like rain, time that will be spent whether it helps to grow things or not, and thus I reclassified labour as a renewable resource and the overall ELR dropped to 2.0 – the typical (but arbitrary) threshold for a ‘sustainable’ system.

The same approach dramatically improved the economics of the gardens too. Initially I calculated a benefit to cost ratio for the gardens by dividing the dollar value of the produce harvested by the value of materials and labour put in. When I costed labour at the minimum wage for a casual farm hand the benefit to cost ratio was just 0.62, meaning that gardeners harvested just 62 cents worth of produce for each dollar invested. However when I removed labour costs from the calculation the ratio improved to 2.55 – $2.55 worth of produce harvested for every $1 spent on materials.

So the gardens I studied turned out to be pretty sustainable, but I wondered if they could potentially do even better. Already gardeners were using a high proportion of recycled inputs such as compost obtained from yard waste and food scraps, and rainwater caught in tanks. This meant the high investment of materials wasn’t necessarily a big issue as they were mostly materials that would go to waste if not used, but what if we used the maximum amount of recycled materials possible? While gardeners were very environmentally minded it can sometimes be hard to do everything ideally – compost takes time to generate and requires a lot of space, water tanks are expensive and the like – but what if all those barriers were removed?

I thus analysed a hypothetical scenario where every material used in a garden that could be replaced with a recycled material was so replaced and in this situation the ELR dropped to just 0.5. Not only is this figure very much in ‘sustainable’ territory, it’s also the second lowest ELR of any crop production system that I’m aware of where this measure has been calculated, with the only one lower than it also being for an urban garden.

In conclusion, while the land available for urban farming may be limited, the productivity of that land can be high and, if performed correctly, the practice can be carried out with very low environmental impact and cost. The results of this study indicate there are few disadvantages in promoting the activity and the major advantage is unlocking an underutilised land resource which is able to provide healthy food without requiring deforestation.

The reliance on volunteer labour creates some questions about the viability of scaling up urban farming, and these are dealt with in my second chapter, which I’m hoping to send out a summary of very soon.