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).

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.

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), 310-319.

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.

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