The cultivation of Stevia rebaudiana outside its native habitat is often constrained by environmental unsuitability. Utilizing organic amendments from water hyacinth and banana stalk presents a cost-effective strategy to enhance its adaptability in suboptimal regions such as lowlands. This study aimed to investigate the effects of water hyacinth biochar and banana stalk compost on the growth performance of S. rebaudiana in a lowland area. A greenhouse experiment was conducted using a completely randomized factorial design. The first factor was water hyacinth biochar dosage (0, 7.5, 15, and 22.5 tons ha-1), and the second factor was banana stalk compost dosage (0, 10, 20, and 30 tons ha-1). Data were analyzed using analysis of variance (ANOVA). Banana stalk compost showing positive and consistent effects on plant height (optimal at 20 tons ha⁻¹), number of leaves, and shoot biomass. In contrast, water hyacinth biochar effects are insignificant on above-ground vegetative parameters. However, there are synergistic and complex interactions between biochar and compost, particularly on root biomass and root volume, as well as secondary metabolite content (stevioside and sucrose), indicating that the appropriate combination ratio is crucial for optimizing crop yield. The optimal combination is 15 tons ha⁻¹ of biochar with 30 tons ha⁻¹ of compost for fresh root weight and 7.5 tons ha⁻¹ of biochar with 10 tons ha⁻¹ of compost for the highest sucrose, as well as 7.5 tons ha⁻¹ of biochar without compost for the highest stevioside.