Vermicomposting harnesses detritivores earthworms to convert organic wastes into nutrient-rich vermicast. While species selection and feedstock quality are well-studied drivers of vermicomposting efficiency, the influence of underlying soil type on earthworm population dynamics during bin- or bed-based systems is less consistently reported for small-scale operations. This study evaluated the population density and growth of Eisenia fetida cultured in three commonly occurring soil types—sandy, loamy, and clayey—when used as the structural fraction (bulking matrix) in vermicomposting beds. Over eight weeks, standardized bins (n = 5 per soil type) were charged with a uniform feedstock mix (pre-composted cow dung: shredded leaf litter: kitchen waste at 2:1:1), maintained at 60–70% moisture, and run under shaded ambient conditions (24–30 °C). Population density, biomass, and cocoon counts were recorded biweekly; substrate physico-chemical parameters (pH, EC, moisture, organic carbon, C:N) were tracked at start and end. Loamy beds showed the highest mean population density (individuals kg⁻¹ substrate) and cocoon production, followed by sandy and clayey beds. Clayey beds exhibited compaction, lower aeration, and transient ammonia accumulation during early weeks. Results support the practical recommendation that a loamy matrix (or sandy-loam blend with structural bulking) optimizes worm performance in low-tech vermicomposting. The study provides a replicable methodology for undergraduate research and highlights moisture control and porosity as key mediators of earthworm fitness.