Published by City Farmer, Canada's Office of Urban Agriculture


Urban Agriculture:
The Potential of Rooftop Gardening


By Joseph St. Lawrence
Joseph St.Lawrence

Report of a Major Project submitted to the Faculty of Environmental Studies in partial fulfilment of the requirements for the degree of Master in Environmental Studies.

York University, North York, Ontario, Canada.
July 29, 1996 [Images are not included here.]

The following web pages contain a major portion of Joseph St. Lawrence's valuable Masters thesis on urban agriculture and rooftop gardening. 15,000 words of the 22,000 word paper are reproduced here. Chapter 1, documenting urban agriculture in general, has not been included nor have most of the illustrations. However the Forward, Chapter 2 (The Site and the Plan), Chapter 3 (Observations), Chapter 4 (Conclusion), and References can be read here in their entirety.

Chapter 2 (The Site and the Plan)
Chapter 3 (Observations)
Chapter 4 (Conclusion), and References


Sometime in the next decade, a migrant or new-born will tip the balance of human population distribution in favour of cities for the first time in history. Ours will become primarily an urban planet. The massive social, economic, and ecological pressures associated with this trend are worthy of attention. Indeed, they were the focus of the second United Nations Conference on Human Settlements (Habitat II), convened in June 1996.

One item on the Habitat II conference agenda was urban agriculture. The phrase conjures contradictions in most minds, but further reflection reveals the vital role it has in the development of sustainable human communities.

This document explores one type of urban agriculture, viz. rooftop gardening. Roof space immediately comes to mind when one considers opportunities for urban agriculture. Rooftops are generally unused spaces, they often have excellent exposure to sunlight and rain water, and they are found in the centre of even the densest urban areas. The initial objective of the project summarised in this report was to explore the economic potential of cultivating these spaces. I have made an effort to explore other issues as well; in fact, I believe that these other issues illustrate the true value of rooftop gardening.

My own interest in this topic followed naturally out of my studies of sustainable agriculture at York University. It was there that I first encountered Bill Mollison's idea of permaculture, which is dedicated to the design of sustainable systems of food production that are integrated with human settlements. Wes Jackson's advice to become native to a place also resonated with me, and I decided to undertake a project in Toronto where I was living and studying during my programme.

The project described in this report is the culminating experience of my Master in Environmental Studies programme. It represents the synthesis of the learning objectives described in the Plan of Study that guided my academic efforts. Two of the procedural issues related to my studies and outlined in the Plan are the need to seek alternatives to the modern industrial food production system, and the need to test the practicality of those alternatives. Much of my work has focused on the first of these issues, and this project is an attempt to address the second. It is my firm belief that agricultural production practices must be dictated by a local environmental context. To test and synthesize the knowledge I have gained, I must therefore seek to apply it in a given setting. My efforts on the rooftop represent this attempt.

Naturally, the conclusions drawn from this inquiry are specific to both the season and the site which hosted the study. Reductionism is one of the great faults of modern agriculture, and attempting to make sweeping conclusions from this small exercise would only perpetuate that folly. What, then, is the use of this investigation? Well, for one it raises some questions about the practice of rooftop gardening, it also illustrates some potentially useful techniques and materials that could be adopted elsewhere in the appropriate circumstances, and finally it illuminates some of the potential pitfalls and benefits associated with this type of cultivation. It is my hope that it will prove useful to anyone interested in undertaking a similar enterprise.

What follows is an account of my experiences gardening on a rooftop in the summer of 1996. The text is more or less narrative, describing my plans, their execution, and general observations. No attempt was made to record data in a scientific fashion. To be of any use, this type of information would need to be collected over numerous seasons, and would require a fairly narrow focus for the activity. I have instead followed the advice of Fukuoka (1978) who suggests that we should train our minds to become like those of children -- not by thinking simply, but ratherby expanding our usual, limited scientific perspective.


I would like to thank Rodger Schwass and Anders Sandberg, my advisors at York University, who greatly assisted me in the development of my Plan of Study; Michael Hough, my project supervisor, who provided valuable guidance and advice; and Mary Lou Morgan and the staff at Field to Table, without whose kind indulgence, this project would never have got off the ground.

Author's note

Gardeners and people in the building trades have been slow to adopt the metric system. Plant spacing is still given in inches in most garden literature, feet are still used to measure lumber, and pounds per square foot is the unit used to describe roof loads. I have not made an attempt to convert all units into metric, but for those who are interested, the relevant conversion factors follow:

For nitrates are not the land, nor phosphates; and the length of fibre in the cotton is not the land. Carbon is not a man, nor salt nor water nor calcium. He is all these, but he is much more, much more; and the land is so much more than its analysis.

Steinbeck, The Grapes of Wrath

Contents (of the complete thesis)

Author's note

1. Urban agriculture

History of Urban Agriculture
North America
Modern Urban Food Production
Wastes as resources
Sewage sludge
Municipal solid waste & waste water
Niche exploitation
Informal employment & economic development
Municipal attitudes
Ecological and social benefits
Preservation of knowledge
Access to land
Food security
Food production
Fungible income
Rooftop gardening

2. The Site and the Plan

The Site
Snow load
Water supply
Light and wind
Indoor lighting
The Plan
Garden structures
Beds and containers
Shade and mulch
Cropping plan
Soil blocks

3. Observations

Cropping Plan
Beds and containers
Shade and mulch
Other greens
Other crops
Soil blocks
Flora and fauna
Roof loads
Social aspects
Waste Reuse
Costs and Revenues

4. Conclusion

Water and light
The Ideal?




2.1 Garden crop data
2.2 Transplant seeding schedule
3.1 Garden yields
3.2 One-time costs
3.3 Ongoing costs
3.4 Crops recommended
3.5 Crops not recommended


2.1 The warehouse roof
2.2 The garden
2.3 Packing skid
2.4 Bed construction
2.5 Typical plantings
2.6 Promotional pamphlet
3.1 New Zealand spinach seeds


2.1 Field to Table warehouse
2.2 Work area
2.3 Finished garden bed
2.4 - 2.8 Bed filling procedure
2.9 Corn crates
2.10 Blocks and block maker
3.1 Planting scheme 1
3.2 Planting scheme 2
3.3 Wind protection
3.4 Mulch
3.5 Bean poles
3.6 The productive rooftop

Chapter 2 (The Site and the Plan)
Chapter 3 (Observations)
Chapter 4 (Conclusion), and References

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Revised February 24, 1997

Published by City Farmer
Canada's Office of Urban Agriculture