Marie-Curie IAPP ‘Green Roof Systems’ Project
The Green Roof Research Conference 18-19 March 2013, Sheffield
Plant growth responses to different growing media for green roofs Abigail Graceson, Martin Hare, Jim Monaghan and Nigel Hall Harper Adams University Introduction Successful development of vegetation enhances a green roof system’s ability to deliver environmental benefits. There have been studies which assess plant growth responses to growing media depth (Rowe et al., 2012), organic matter content (Nagase and Dunnett, 2011) and irrigation frequency (VanWoert et al., 2005). Both Molineux et al. (2009) and Thuring et al. (2010) have considered the effect of inorganic substrates on plant growth over two months and four months respectively but Rowe et al. (2012) highlighted that vegetation performance can change over a number of years. The aim of this study was to assess the effect of the type of inorganic substrate and the amount of composted green waste in growing media for green roofs on plant growth responses such as shoot biomass and species richness.
Overview of Methodology Green roof simulation decks (figure 1) 1 m x 1 m were filled with growing media made using crushed brick, crushed tile or fly ash pellets amended with 20% v/v or 30% v/v composted green waste (figure 2) to a depth of 150 mm. Green roof meadow seed mix was sown at a rate of 2 g m-2 and plant growth responses measured after 2 years.
Figure 1 – Green roof simulation deck Figure 2 – Crushed brick (top left), crushed tile (top right), fly ash pellets (bottom left) and composted green waste (bottom right)
Marie-Curie IAPP ‘Green Roof Systems’ Project
The Green Roof Research Conference 18-19 March 2013, Sheffield
Key Findings Crushed brick had a limiting effect on growth of sedums due to higher levels of salts (Figure 3a). Shoot biomass of sedums increased when the amount of composted green waste was increased but this was less extreme on growing media made with crushed brick than on growing media made with crushed tile or fly ash pellets as the crushed brick limited sedum growth (Figure 3a). On growing media made with crushed brick there was a greater increase in herb shoot biomass than on growing media made with crushed tile or fly ash pellets when the amount of composted green waste was increased (Figure 3b).
a.
30% CGW
b.
20% CGW Shoot biomass
Shoot biomass
20% CGW
Brick
Tile
Fly ash
Brick
30% CGW
Tile
Fly ash
Figure 2 – Shoot biomass of a. sedums and b. herbs on green roof simulation decks
Species richness also increased on growing media made with crushed brick but decreased on growing media made with crushed tile or fly ash pellets (Figure 4). The reduced level of competition from sedums enabled better development of a greater number species. 30% CGW
Species richness
20% CGW
Brick
Tile
Fly ash
Figure 4 – Species richness on green roof simulation decks
Further Reading Nagase, A. and Dunnett, N. 2011. The relationship between percentage of organic matter in substrate and plant growth in extensive green roofs. Landscape and Urban Planning, 103 (2), 230-236. Molineux, C. J., Fentiman, C. H. and Gange, A. C. 2009. Characterising alternative recycled waste materials for use as green roof growing media in the U.K. Ecological Engineering, 35 (10), 1507-1513. Rowe, D. B., Getter, K. L. and Durhman, A. K. 2012. Effect of green roof media depth on Crassulacean plant succession over seven years. Landscape and Urban Planning, 104 (3-4), 310319. Thuring, C. E., Berghage, R. D. and Beattie, D. J. 2010. Green roof plant responses to different substrate types and depths under various drought conditions. Horttechnology, 20 (2), 395-401. VanWoert, N. D., Rowe, D. B., Andresen, J. A., Rugh, C. L. and Xiao, L. 2005. Watering regime and green roof substrate design affect Sedum plant growth. Hortscience, 40 (3), 659-664.