This research investigated the potential of Costus bullatus bagasse ash as an eco-friendly additive for stabilizing problematic lateritic soils when combined with cement or lime. Soil samples were treated with different concentrations of bagasse ash (0–12%) alongside a fixed 8% content of either cement or lime. A rigorous testing program evaluated key engineering properties of the stabilized soil mixtures, including compaction characteristics (maximum dry density and optimum moisture content), consistency limits, California bearing ratio (CBR), and unconfined compressive strength (UCS). Results showed both cement and lime mixtures exhibited improved geotechnical performance relative to the native soil. However, cement mixtures generally outperformed corresponding lime mixtures. Consistency limits increased more substantially for lime treatments, highlighting cement's comparative benefits. Bagasse ash incorporation led to density reductions but enhanced bearing capacity and strength parameters substantially. Chemical analysis confirmed the bagasse ash met guidelines for pozzolanic reactivity. Outcomes were consistent with prior literature, validating Costus bullatus bagasse ash as an effective and sustainable indigenous soil modifier. Overall, findings demonstrate the viability of utilizing optimum dosage proportions as a ground improvement solution for problematic lateritic deposits.