Extensive Green Roof Substrates Research Articles

Evaluating a Natural Zeolite as an Amendment for Extensive Green Roof Substrate

This research examined soilless green roof substrate blends on an existing modular extensive green roof in Denver, Colorado, USA. Substrate blends evaluated include an extensive green roof substrate, Green Grid® and Green Grid® plus varying percentages of ZeoPro™ H-Plus. Plant taxa used included Sedum acre L., Sedum album L., Sedum spurium Marsch-Bieb. ‘Dragon's Blood’ and S. spurium ‘John Creech’. Substrate blends were evaluated based on plant taxa growth performance. Data collected included digital images to measure plant area covered using digital image analysis (DIA) and substrate volumetric moisture content (VMC). All data were analyzed over two growing seasons using the GLIMMIX procedure in SAS as multiple comparisons of substrate blends for each taxa, DIA data were analyzed from eight dates and VMC data were analysed from seven dates. The addition of zeolite (ZeoPro™) to the typical extensive green roof substrate improved establishment year plant cover for S. acre and S. album but hindered overwintering. Conversely, the two cultivars of S. spurium did not show a benefit of plant cover from the addition of ZeoPro™ in the first year but did the second year. As the percentage of ZeoPro™ in the substrate increased, VMC also increased.

Moisture Content of Extensive Green Roof Substrate and Growth Response of 15 Temperate Plant Species during Dry Down

Success of extensive green roof vegetation depends primarily on associated plant species' ability to survive the low moisture content of the substrate. As a result of the well-drained nature of the substrate, plants adaptable to dry, porous soils are primarily used in extensive green roof applications. Although Sedum species have dominated the plant palette for extensive green roofs, there is growing interest in expanding the plant list for extensive green roof systems. To effectively select suitable plants, species need to be evaluated in terms of their response to gradual and prolonged dry down of the substrate. A study to determine the relative rates of dry down for 15 species was conducted in greenhouse trials. During dry downs that extended over 5 months, the substrate of succulent and herbaceous species dried down at different rates. The change in moisture content of the substrate was not consistent among succulent and herbaceous plant species during the initial 18 d of dry down. Despite differences in rate of dry down, the succulent species, as a group, maintained viable foliage for over five times longer than the herbaceous species. The revival rates of the succulent species were nearly double those of the herbaceous species. Therefore, not only are succulent species more likely to survive during periods of drought, but these species are more likely to resume growth soon after water is again made available.

An initial experimental assessment of the influence of substrate depth on floral assemblage for extensive green roofs

Extensive green roofs have the potential to be used as mitigation tools to compensate for urban habitat loss, but there is little information about how closely these systems emulate ground-based habitats. This study investigated the effect of limited substrate depth on plant assemblages in the initial phase of growth in extensive green roof substrates. Five replicate mesocosms (1 m 2) for each of three design treatments: (A) 10 cm aggregate depth with green roof drainage and solid floor, (B) 15 cm aggregate depth with green roof drainage and solid floor, and (C) 15 cm aggregate depth on top of bare earth; were positioned at ground level. Each mesocosm had an identical growth substrate and was seeded with the same seed mix. Plant assemblages were analysed using point-quadrat methods. Significant differences in species composition were observed between treatments that seemed to be related to water availability. Even the deep (15 cm) solid floor green roof treatment showed many significant differences in floral assemblage compared to the identical treatment (C) where plants had access to water in the soil profile. Therefore, it is not possible to exactly recreate most ground-based urban habitats on roofs by simply copying the soil characteristics and floral composition found on the ground. Like for mitigation for habitat loss using extensive green roofs requires the careful manipulation of design elements in order to counteract the limited water availability on green roofs.