Evaluation of crassulacean species for extensive green roof applications

Green roofs are an emerging technology in the United States that alleviate several environmental problems. Because environmental conditions are often more extreme on rooftops, many xerophytic plants are ideal for extensive green roofs. However, limited studies have been performed to determine the characteristics necessary to sustain plant life for green roof applications in the Michigan region. Therefore, a greenhouse experiment determined the effect of watering regime on plant stress for succulent and non-CAM plants. Results indicate even after the four month period, Sedum spp. were able to survive and maintain active photosynthetic metabolism, relative to the non-CAM species. Two field studies performed over 16 months on simulated roofing platforms evaluated 25 Crassulacean species. For both field studies, overwintering survival was dramatic, as only 47% survived in the deepest substrate of 7.5 cm. Results indicated deeper substrates promoted greater survival, growth, and faster coverage, however, in the shallowest depth of 2.5 cm, several species continued to persist. Relative abundance was highest for Phedimus spurius Raf. 'Leningrad White,' Sedum acre L., S. album 'Bella d'Inverno' L., and S. middendorffianum L. Subsidiary species included S. hispanicum diploid L., S. kamtschaticum Fisch., S. sediforme J., S. spurium Bieb. 'Summer Glory,' S. dasyphyllum 'Burnati' L., and S. reflexum L.