Biochar makes green roof substrates lighter and improves water supply to plants

Abstract

Green roofs are increasingly being built to manage stormwater runoff in cities. Water-retention additives such as biochar could be a useful way of increasing substrate water holding capacity (WHC) and therefore stormwater retention without increasing substrate weight loading. If this also increases plant available water (PAW), plant selection could be expanded to species with higher water use, further reducing stormwater runoff by drying substrates after rain. We examined the effects of adding one type of green waste biochar (0, 10, 20, 30 and 40%, v/v) to two scoria-based substrates (with or without added organic matter) on WHC, bulk density, PAW and days taken to reach permanent wilting po..