A Comparison of Organic Matter Amendments for Use in Extensive Green Roof Substrates

Abstract

Organic matter is important for water retention and nutrient availability in green-roof systems. Yet few quantitative green-roof studies provide data for various sources of organic matter (OM). Coconut coir (CC), rice hulls (RH), SmartLeaf® (SL), and mushroom compost (MC) were used as green roof substrate amendments. The effects of OM on water-holding capacity, nutrient availability and plant establishment were measured. Growth of Phedimus kamtschaticus was greater with MC or SL compared to CC or RH. Substrate moisture and nutrient availability were significantly affected by OM source during an 8-month rooftop experiment and a 6-month growth chamber study. Coconut coir showed high moisture retention, low nutrient availability and low aboveground biomass, indicating that nutrient availability is crucial to successful plant growth and establishment on a green roof. Composted materials such as MC and SL that have higher levels of available nutrients, promote better growth than unprocessed materials like RH and CC.