Use of compost as amendment for soilless substrates of plants in green roof installations

The effect of amendment with compost obtained from food waste in soilless substrate was evaluated with respect to the growth of Sedum reflexum, Sedum palmieri, Sedum acre, Sedum spurium and Sempervivum tectorum under conditions simulating a green roof in central Italy. Plants were grown in a mix of soilless media developed for green roofs with 5 and 10% v/v amendment and a starter dose of fertilizer. The 5% amendment produced a significant increase of fresh and dry weight on Sedum reflexum plants growing in pots after 15 weeks. A long-term experiment was conducted in containers with 10% compost and the five species transplanted together with a fixed pattern. After 139 days, the compost amendment produced a significant increase on surface coverage for Sedum reflexum, Sedum palmieri and Sempervivum tectorum. The evaluation on day 251, at the end of the winter season, showed a reduced growth rate in the control, while the compost treatment produced significant increases for the Sedum species. The increase in plant weight was significant for Sedum palmieri, Sedum acre and Sempervivum tectorum. The N content at day 251 was higher in plants with compost, suggesting a compensation of the nutrient depletion and cold damage during the winter.