The study aimed to determine the influence of soil amendments on the growth and yield performance of onion bulbs under the Lagangilang condition. Specifically, it aimed to assess the efficacy of different soil amendments on the growth and yield of bulb onions; the combined effect of soil amendments and disease infestation on the growth and yield of bulb onions; identify which soil amendments treatment enhances the yield of bulb onion and identify the most prevalent insect pest and diseases affecting the growth and yield of bulb onion. The Randomized Complete Block Design (RCDB) replicated dour times was employed in the study. The treatment was T0 No ameliorant, T1 Biochar, T2 Vermicompost, T3 Carbonized Rice Straw, T4 IFSU Bio-organic. The results of the study showed that among the treatments, plants in Treatment 3 were the tallest with the longest leaf. Meanwhile, Treatment 1 obtained the highest fresh weight, the bulb’s dry weight, the number of marketable yields, and the highest income as indicated. Soil amendments have a positive effect in increasing the yield of onion plants. The experimental plant, on the other hand, was attacked by different diseases and insect pests, but the most prevalent disease was the black stalk rot with varying levels of severity on the soil amendments applied. The analysis of variance shows insignificant among the treatments as to plant height, length of the leaf, and infestation of insect pests and diseases. However, highly significant differences among all treatments were found in bulb size, marketable yield, fresh weights, and dry weight.