Turfgrass Use on Intensive and Extensive Green Roofs

Turfgrasses are a promising means of cultivation for covering roof tops of buildings. Their low and frequently prostrate growth, their ability to provide total surface coverage, the increased tolerance of specific species to several stress factors such as drought, heat, solar irradiance, and air pollution make them good candidates for green roof plant material. In intensive green roof systems the selection of the substrate is of major importance since it was found to affect Festuca arundinacea growth while at the same time contributes to the roof weight. The effort to minimize the load applied onto the building necessitates the use of substrate amendments that are lightweight and usually coarse textured. However special care should be given to the environmental fate of the agrochemicals applied on these coarse textured substrates since nitrates were found to leach in excess from a sandy loam soil amended with perlite (30:70% v/v mix). In addition metalaxyl-m leached from the substrates in a manner that was reversely proportional to the amount of organic matter in the substrate. In extensive green roofs trials that included four different substrates with variable depth (7.5 and 15 cm) and two irrigation regimes (high and low) establishment rate of Zoysia matrella 'Zeon' was generally improved by substituting peat with compost in the substrates but performed poorly under water stress conditions. The stress was alleviated by increasing substrate depth from 7.5 to 15 cm. Further research is necessary to establish rigid standards for the use of turfgrasses on green roofs.