<p>Chicken feather waste (FW) is abundant and low-cost nitrogen source for fertilizer production but difficult to degrade due to its keratin content. Its composting often requires keratinolytic inoculum, which increases cost and complexity. However, under suitable composting conditions, indigenous microorganisms may efficiently drive FW decomposition without external inoculum. This study investigated the co-composting of FW and banana peels (BP), a potassium-rich agricultural residue, without inoculum, and examined the compost products quality and its effect on mustard green (<i>Brassica campestris</i> L.). Mixtures containing 60% (FW-60), 30% (FW-30), and 15% FW (FW-15) were composted in 200-L vessels over 56 days. Physicochemical revolution showed an effective composting process with a distinct thermophilic phase and the reduction of total carbon. Final composts contained 8.3–8.8% N and 2.9–3.9% K₂O. Germination indices exceeded 120% for FW-30 and FW-15, confirming maturity and no phytotoxicity, whereas FW-60 inhibited seed germination in undiluted extracts. Field experiments demonstrated that FW-15 and FW-30 significantly enhanced mustard green yield, height, and leaf width compared to chicken manure fertilizer and the unfertilized control (<i>p</i> &lt; 0.001). These results demonstrate that co-composting FW with BP could proceed effectively under the absence of innoculum to produce nutrient-enriched organic fertilizer, while simultaneously valorizing poultry waste and mitigating environmental pollution risks.</p> Graphical Abstract <p></p>