<![CDATA[Background: Cauliflower (Brassica oleracea var. botrytis L.) is a high-value horticultural crop whose productivity is influenced by vegetative growth, nutrient availability, and curd development. However, information on the interactive effects of gibberellic acid (GA₃) and organic fertilizer, particularly under different nutrient inputs, remains limited. This study aimed to determine the individual and interactive effects of GA₃ concentration and guano fertilizer dosage on the growth and yield of cauliflower. Methodology: The experiment was conducted in Sedati, Ngoro District, Mojokerto Regency, using a factorial Randomized Complete Block Design with two factors, three replications, and 48 experimental units. GA₃ factor was applied at 0, 150, 200, and 250 ppm, while the fertilizer treatments consisted of NPK 16-16-16 as a reference and guano fertilizer at 40, 60, and 80 g plant⁻¹. Plant height, canopy diameter, curd weight, and aboveground biomass were recorded and analyzed using analysis of variance followed by the 5% Honestly Significant Difference test. Findings: Significant interactions between GA₃ concentration and guano dosage were observed for plant height at 28, 35, and 42 days after transplanting and for curd weight at harvest. The combination of 200 ppm GA₃ and 60 g plant⁻¹ guano produced the highest plant height, reaching 15.94, 18.72, and 23.22 cm at 28, 35, and 42 days after transplanting, respectively, and the highest curd weight of 524.78 g plant⁻¹. Independently, 200 ppm GA₃ produced the greatest canopy diameter (55.49 cm) and aboveground biomass (663.39 g plant⁻¹) at 42 days after transplanting and harvest, respectively. Guano at 60 g plant⁻¹ produced aboveground biomass (641.11 g plant⁻¹) comparable to NPK (634.19 g plant⁻¹). Contributions: These findings demonstrate that GA₃ effectiveness depends on organic nutrient input and highlight 200 ppm GA₃ combined with 60 g plant⁻¹ guano as a promising treatment under the experimental conditions.]]>
