Roof making food? A reality

As the world's population becomes increasingly urbanized, issues of urban sustainability are becoming more important. Cities, particularly in North America, are at present quite unsustainable, using far more land and resources than they physically encompass. One proposed alternative to the current system is the nurturing of a more localized urban agriculture. Unfortunately, land which has traditionally been used for agriculture within our urban areas is now in high demand and vulnerable to development. As a result, rooftop agriculture, combined with green roof systems, has become an attractive possibility. However, the efficiency of green rooftop agriculture has not been extensively tested.

One of the most common barriers to the adoption of sustainable alternatives is lack of confidence and easily accessible straightforward and tested experience to depend on. Previous work on rooftop agriculture, and particularly the use of green roofs for agriculture, has been largely theoretical. Therefore, a demonstration project was conducted to evaluate perceived barriers to rooftop vegetable production in the green roof context. The project goal was to evaluate the feasibility of green roof technology for urban agriculture for Peterborough and elsewhere, testing the hypothesis that green rooftop agriculture is viable as an urban agricultural alternative. Soil temperature, soil moisture, crop health, quality, and productivity were monitored. The results for different soil treatments, of mulch, shadecloth, and bare soil, were compared. In this way the suitability of various crops, varieties of crops, and soil treatments to rooftop conditions were evaluated. Background research was conducted to provide context for the project, and the benefits and barriers to green roofs and urban food production were detailed. Available literature on the special conditions of rooftop agriculture was also examined. All of these were useful in framing the demonstration project results.

The demonstration project was conducted on the green roof located on the Trent University Environmental Sciences building, Peterborough, Ontario. 14 common vegetable crops were planted in a 7.5 x 30 m plot, subdivided into four equal beds. 2 different varieties of each crop were planted, chosen for their possible suitability to rooftop conditions. Each of these was planted in two beds, one covered with mulch or shadecloth, depending on the crop, the other uncovered. The productivity of individual crops and beds was monitored separately. In addition, wind speed, soil temperature and moisture were monitored on the rooftop and at ground level. The results were then compared to each other, to the ground level results, and also to official Ontario Ministry of Agriculture, Food, and Rural Affairs crop productivity statistics.

From my results it was not possible to conclude that green rooftop food production can serve as a viable agricultural alternative in any broad commercial sense. However, it can be concluded that, on a green roof such as the one considered here, rooftop growing conditions are not substantially different from those on the ground. Therefore, it is possible to conclude that such a development is possible on a small scale, given experience and a broader incorporation of green roofs such as this one into the urban landscape.