Investigation of Dynamic Cycles of Semi-Extensive Green Roof

The phenological study of green roofs has been limited although it is crucial to the creation of aesthetically pleasing and seasonally interesting green roofs. This study aimed to investigate the dynamic change (constant change) of semi-extensive green roofs and the following two points were studied on the green roof in Rotherham, Northern England from February to November 2006: (1) Flower performance and plant growth pattern (2) Effect of planting design (plant species diversity and planting density) on flower performance and plant growth. This green roof was installed in the summer 2005 and 54 species of perennials, ornamental grasses and bulbs were planted in 10 cm (areas with gravel mulch) and 20 cm (areas without mulch) of substrate. 32 quadrats (50 cm x 50 cm) were set up through the combinations of plant species diversity (High and Low), planting density (High and Low), aspect (South East, South West, North East, North West) and covering gravel mulch (with and without). Results showed that throughout 10 months, at least 3 species flowered in each month and the highest number of flowering species was observed in June. The growth characteristics of individual plant species over time were categorized into 6 patterns of coverage and vertical growth pattern. It was shown that plant species diversity might affect overall flowering succession and dynamic change and planting density might affect interaction between plants. In areas of high plant species diversity, there were more opportunities for a longer flowering term, more seasonal interest and dynamic change than areas of low plant species diversity. In areas of low planting density, individual plants generally produced better growth than those in high planting density. However, these tendencies were affected strongly by the combination of species used. Therefore, it is important to be aware of individual plant growth characteristics such as plant size (coverage and vertical), phenological growth pattern and flowering season to create aesthetic and seasonal interesting green roofs.