Evaluation of different establishment methods of sedum cuttings for summer vegetation of green roofs in Venetian Plain conditions

Sedum species are the most commonly used plants to vegetate green roofs because of their tolerance to extreme conditions. Despite the easier and faster establishment of sedums by plugs or mats, the direct spreading of cuttings is still an interesting cost-effective installation method, especially for large-scale roofs. To improve cutting establishment in the difficult conditions of the Venetian plain during summer, a three-way experimental design was set up on June 5, 2015. Rooted and unrooted cuttings of five Sedum species (Sedum acre, S. album, S. reflexum, S. sexangulare and S. spurium) were compared with and without ground cover with non-woven fabric (fabric) in the first four weeks after cutting spreading (WAS). Cuttings survival and plant growth was evaluated over 20 weeks: 4 WAS (at fabric removal), after 12 and 20 WAS. Plant growth was measured by means of growth index, and shoot and root dry weights. After 4 WAS sedum cuttings were negatively affected by covering with fabric as only 68.5% of cuttings had survived compared to 98.5% of the uncovered control. Shoot and root dry weights were also negatively affected by fabric cover. At the end of the study both the fabric cover and Sedum species affected plant survival. Uncovered treatment exhibited better survival compared to the fabric cover (71.5 vs. 60.5%) while S. spurium and S. sexangulare had only 50% survival compared to the over 80% survival for S. acre. The sedum cuttings of the fabric cover treatment recovered over time, providing similar growth as the uncovered treatment at the end of the experiment. Sedum spurium had the highest growth index, shoot and root dry weights and S. album growth was also good. Pre-rooted cuttings did not affect survival but favored aerial growth of S. spurium and S. reflexum.