This study has shown that the establishment of perennial plants on green roofs is possible and that these plants can survive over two growing seasons. The most effective substrate for plant biodiversity varied over time, but admixes (blends of two or more different aggregates) performed particularly well in terms of both coverage and plant species richness. In particular, red brick, clay pellets and a combination of the two offer very promising substrates for the maximization of plant diversity and a more even establishment of plants. For poorer performing substrates, coverage and species richness is enhanced (in most cases) with greater substrate depth, and depth alone can vastly improve the performance of a particular aggregate that may not be very successful if used at shallow depths of 5.5 cm. It would be interesting to see if this trend changes in subsequent years, particularly with regards to different weather patterns. Therefore the hope for future research is long-term monitoring of extensive green roofs using a range of novel recycled substrates, to determine just how resilient these urban habitats could be. Furthermore, their abilities to support communities of associated insects and birds need to be tested over extended periods of time.