This research compares the stormwater retention performances of an organic waste growing medium extracted from the widely available Psidium guajavala L species in Sri Lanka. Rainfall gauges were manually constructed to outsource accurate precipitation data, and the study was conducted throughout the entire month of January 2023. A stormwater retention curve was constructed for the Biochar, Sawdust and Wood bark substrates and the hotspots were compared. Furthermore, the results were validated using a volumetric comparison of water retention. The experimental outcomes have shown that Biochar exhibits strong water retention ability and enables the overlaying vegetation to acquire nutrients without external obstacles. The main reason for this exceptional performance was biochar's low evaporation levels and high porosity. In contrast, Sawdust was found to be the worst performer in terms of water retention due to its high thermal conductivity. These experimental studies were rationalised by outsourcing the specimen from the same tree. Our recommendations suggest that the biochar manufacturing industry needs to be improved in the future since it provides a sustainable and effective alternative in terms of eco-friendly substrates.