As of 2022, the Saint-Laurent neighborhood requires new roofs to be either green or reflective (white). IGA, a supermarket chain in Canada, rose to the challenge of needing at least 50% of the building roof area covered with a green roof system. The solution? A large-scale urban rooftop farm, complete with vegetable and flower gardens, beehives, and full-time employed farmers to keep the project running.
Similar to more traditional agricultural systems, IGA Rooftop Farm utilizes a unique growing media which contains around 35% organic matter by volume. The media is Ecocert certified, and allows for the produced food to be qualified as organic. Interestingly, in an interview with Chris Grallert, President of rooftop gardening company Green City Growers, organic matter content was discussed. Grallert said that “Once you start to get above 10% organic matter, all kinds of nutrients cycling… get out of whack.” A study from Cornell University corroborates Grallert, noting that quality soils contain 3-6% organic matter to preserve biodiversity.
Despite the discourse, clearly the growing media works for IGA. In a case study focused on the IGA rooftop farm, this contradiction was noted:
“Typically, green roof media has a very low organic content to ensure minimal maintenance and adequate drainage, as well as minimize compaction. These types of growing media are not adequate for food production and need to be adapted to support vegetable growth. Active monitoring and adjustments over the course of four years supported the development of new organic green roof soils specifically designed for vegetable production on green roof”
Considering the difference in legacy knowledge from traditional agriculture and new knowledge around green roofs, there is seemingly a gap in research for ideal organic matter content in rooftop growing media versus traditional soil composition.
Besides growing media, IGA engineered a waterproofing system that still allows for proper drainage. Water for the irrigation system is partially recovered from the supermarket’s air conditioning system, as well as stormwater recovery. The waterproofing system consists of an insulating layer between the plants and the physical roof, which both protects the roots and helps minimize the store’s energy consumption.
The IGA rooftop farm is highly efficient, producing:
- broccoli
- cauliflowers
- parsnips
- carrots
- cabbages
- melons
- artichokes
- greens
- small roots (turnips and radishes)
- cherry tomatoes
Head Grower Pierre-Antoine Jacques highlighted some of the benefits of the IGA Rooftop Farm, saying “perfect light exposure, the absence of deer and other small mammals, near-perfect “field” conditions very early in the season, cover crops, green manure, minimum soil disturbance and regular additions of compost” allow for the rooftop farm to simulate a traditional rural farm. The same ecosystems (worms, bacteria, pollinators, etc.) have come to exist on the roof, making it a worthwhile endeavor.
The IGA Rooftop Farm highlights an alternative option to rooftop gardening besides more complex systems like hydroponics or greenhouses. It combines traditional knowledge with green practices, allowing for a use of urban space that directly benefits its consumers. The Rooftop Garden also includes the community by hosting events and allowing for consumers to see exactly where their produce is coming from, minimizing pesticide usage and transportation costs. IGA is meeting qualities of just sustainability via its rooftop system.