Substrate Depth Influences Sedum Plant Community on a Green Roof

Abstract

<jats:p>Because the waterproofing membrane beneath green roofs is estimated to last at least 45 years, long-term plant performance beyond initial establishment is critical. Plants that survive initially on a green roof may not exist in the long term because of variability in climate and other factors. This study evaluated the effect of green roof substrate depth on substrate moisture, plant stress as measured by chlorophyll fluorescence, and plant community development and survival of 12 <jats:italic>Sedum</jats:italic> species over 4 years in a midwestern U.S. climate during 4 years of growth. Plugs of 12 species of <jats:italic>Sedum</jats:italic> were planted on 8 June 2005 and evaluated biweekly for absolute cover (AC). Most species exhibited greater growth and coverage at a substrate depth of 7.0 cm and 10.0 cm relative to 4.0 cm. For the species evaluated, substrate depths of at least 7.0 cm are highly recommended. AC of <jats:italic>Sedum</jats:italic> was significantly greater at this substrate depth than at 4.0 cm. Mean volumetric moisture content of the three substrate depths followed the same pattern as AC. When averaged over time, the 4.0-cm substrate depth held less moisture than depths of 7.0 or 10.0 cm, whereas the 7.0- and 10.0-cm substrate depths were statistically the same. Species exhibiting the greatest AC at all substrate depths were <jats:italic>S. floriferum</jats:italic>, <jats:italic>S. sexangulare</jats:italic>, <jats:italic>S. spurium</jats:italic> ‘John Creech’, and <jats:italic>S. stefco</jats:italic>. In general, species that are less suitable at these substrate depths are <jats:italic>S</jats:italic>. ‘Angelina’, <jats:italic>S. cauticola</jats:italic> ‘Lidakense’, <jats:italic>S. ewersii</jats:italic>, <jats:italic>S. ochroleucum</jats:italic>, and <jats:italic>S. reflexum</jats:italic> ‘Blue Spruce’.</jats:p>

Green roof vegetation for North American ecoregions: A literature review

“…Overall, succulents were found to perform best in 7-10 cm of growth media across northern regions according to specific green roof design parameters (Table 2), but were found to tolerate 5-cm-deep substrates as well. Findings in the South Central Great Lakes ecoregion revealed that succulents performed marginally on very shallow (2.5-5 cm depths) unirrigated green roof research plots, better in 5-7.5 cm deep substrates (Durhman et al, 2007;Getter and Rowe, 2009) and better yet in 7-10 cm deep substrates (Getter and Rowe, 2008a,b,c). In general, Sedum were found to be very reliable genus as they were found to have great endurance for drought tolerance.…”

“…A similar investigation in Michigan also found sensitivity of Sedum ssp. roots to low temperatures in shallow substrates (2.5-7 cm), however plants were not growing on rooftops but on elevated platforms (Durhman et al, 2004(Durhman et al, , 2007Getter and Rowe, 2009). Some Sedum species also had poor performance in hot humid regions, where they did not tolerate the hot and humid evenings during summer (Livingston et al, 2004).…”

The role of green roof technology in urban agriculture

“…Factors determining plant survival include media composition and depth 11,12 , incoming solar radiation 13 , climate and most importantly soil moisture [14][15][16] . Insufficient moisture can be remedied by altering media composition and depth or with irrigation if available.…”

Performance of Two Simulated Green Roofs in the Mediterranean Area

“…There have been a number of studies on the development of green roof vegetation over reasonably long periods, many of them concluding that plant diversity is dependent on the properties of the substrate (Bates et al, 2013;Thuring & Dunnett, 2014). Other studies have identified a relationship between the evolution of vegetation and the availability of water, as well as the depth of the substrate (Dunnett & Nolan, 2004;Getter & Rowe, 2009;Rowe et al, 2012).…”