A building of Boston University was the host of an interesting experiment: the recycling of the air inside the structure – rich in CO2 – to increase the yield of the gardens placed on the roof.

The results seem satisfactory, and could open up new prospects for a green turnaround for cities.

Green roofs and urban gardens

In addition to the aesthetic-ornamental value, green roofs also play a functional role in regulating the microclimate and local pollutants, as well as in terms of thermal insulation and permeability. If the surfaces are then exploited for the placement of urban gardens, it is also possible to obtain a supply of local and healthy food resources.

However, plants grown on rooftops are often smaller and less healthy, as they are exposed to stronger solar radiation and currents, and have lower soil moisture.

The Boston Experiment

To overcome these problems, a research group has devised a fertilization system for the plants placed on the roofs of a Boston University building through the reuse of the CO2 expelled from the buildings’ ventilation systems.

The experimentation involved the cultivation of corn and spinach. The latter were chosen as more sensitive to CO2, while corn acted as a control to study the influence of other aspects related to the positioning near the air vents (such as higher temperatures).

The results

Experimentation showed a four-fold increase in spinach biomass compared to control plants. Furthermore, good results were also observed for corn, which grew two to three times more than normal, indicating that there are environmental factors other than CO2 affecting growth.

An additional factor to take into account in the model is the wind speed, which is estimated to have reduced plant growth by about two times.