Post-mining land rehabilitation offers potential for integrating ecological restoration with biomass-based energy production; however, optimal silvicultural configurations for degraded substrates remain insufficiently quantified. This study evaluated the interactive effects of planting density (1×2 m vs. 2×2 m), planting hole volume (10×10×10, 20×20×20, and 30×30×30 cm), and growing media composition (100% topsoil vs. 70:20:10 topsoil:solid decanter:biochar) on growth performance and fuel quality of Calliandra calothyrsus in a 18-month factorial field experiment on post-coal mining land in East Kalimantan, Indonesia. Planting density and rooting volume showed significant interaction effects on biomass accumulation (two-way ANOVA, p < 0.05), with 1×2 m spacing combined with 30×30×30 cm planting holes producing the highest yield (62 t ha⁻¹ at 24 months). In contrast, restricted rooting volume (10×10×10 cm) consistently limited growth irrespective of media composition. Biomass exhibited high fuel quality across treatments, with a net calorific value of 21.99 MJ kg⁻¹, low ash content (1.05%), and minimal sulfur concentration (0.05%), corresponding to an estimated theoretical energy potential of 386 MWh ha⁻¹. These results provide experimental evidence that planting density and soil preparation jointly regulate productivity of C. calothyrsus on degraded substrates and inform management strategies for biomass-oriented restoration of post-mining landscapes Keywords: Calliandra calothyrsus, short rotation coppice, post-mining rehabilitation, biomass energy, silviculture optimization.