Background <p>Declining soil fertility remains a major constraint to vegetable production in tropical regions, necessitating sustainable and efficient nutrient management strategies. This study evaluated the effects of biochar, cow manure and their co-application on growth, yield and soil chemical properties of spinach (<i>Spinacia oleracea </i>L.) under field conditions in western Uganda. A field experiment conducted in 2025 tested four treatments: control, biochar alone (50 t ha⁻¹), cow manure (20 t ha⁻¹), and co-application of biochar (25 t ha⁻¹) and cow manure (10 t ha⁻¹), arranged in a Randomized Complete Block Design (RCBD). </p> Results <p>Results indicate that the co-application of biochar and manure produced the tallest plants (45.6 cm), approximately 120% taller than the control (20.7 cm), and increased plant height by 35.7% compared to biochar alone. Similarly, the highest yield (22.5 t ha⁻¹) was obtained under the co-application of biochar and manure. Specifically, the co-application of biochar and manure significantly increased spinach yield by 78% compared to biochar alone, while a non-significant increase of 31.1% was observed relative to manure alone. Furthermore, principal component analysis (PCA) revealed strong positive associations among growth and yield parameters and soil total N, K, EC and pH. </p> Conclusion <p>Overall, the co-application of biochar and manure enhanced spinach productivity and soil fertility in tropical systems. </p>