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Extensive Green Roof Research Program at Colorado State University
Bousselot, J., J. E. Klett, AND R. Koski. Extensive Green Roof Research Program at Colorado State University. Presented at Seventh Annual International Greening Rooftops for Sustainable Communities Conference, Awards and Trade Show , Atlanta, GA, June 03 - 05, 2009.
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In the high elevation, semi-arid climate of Colorado, green roofs have not been scientifically tested. This research examined alternative plant species, media blends, and plant interactions on an existing modular extensive green roof in Denver, Colorado. Six plant species were evaluated for potential use in green roof systems. Antennaria parvifolia, Eriogonum umbellatum, Opuntia fragilis, Sedum lanceolatum, and Bouteloua gracilis are natives of shallow, rocky, well-drained locations in Colorado and Delosperma cooperi is a native of South Africa. Media blends evaluated include Green Grid® media (Weston Solutions, Inc.) and Green Grid® media plus various percentages of ZeoPro™ H-Plus (ZeoponiX, Inc.). Media blends were evaluated for nutrient holding capacity, water holding capacity, as well as plant species growth performance. Plant species used in the media study included Sedum acre, S. album, S. spurium ‘Dragons Blood’ and S. spurium ‘John Creech’; these species were already in use on the existing green roof. The plant interaction study utilized the six alternative species plus Allium cernuum and Sempervivum rubrum in mixed plantings in trays that contained the Green Grid® media or a 1:1 mixture of the Green Grid® media and ZeoPro™ H-Plus. A greenhouse trial screened 23 plant species for relative drought tolerance. All experiments were randomized complete block design (trays for experiments on the green roof were mixed in with the existing trays). Data collected included plant widths and heights, and soil moisture. Soil moisture was measured with a ML2x ThetaProbe (Delta-T Devices Ltd). On a weekly basis throughout the growing season, data were collected and photos were taken to analyze plant growth rates.