Abstract:The study was conducted to determine the viability of producing organic onion under the fully converted area of Ramon Magsaysay Center for Agricultural Resources and Environment Studies (RMC-ARES), Central Luzon State University, Philippines. Specifically, the study aimed to establish the frequency of organic fertilizer and Trichoderma spp. application, employing split application, and determine the yield performance of red onion (bulb type). The research was conducted for two consecutive dry seasons (2014 and 2015). Red Creole variety was used with the following treatments: T1-organic fertilizer alone (8 ton/ha) at planting; T2-organic fertilizer (8 ton/ha) applied twice (at basal and 30 d after transplanting (DAT)); T3-organic fertilizer (8 ton/ha) applied twice (at basal and 30 DAT) + Trichoderma spp. at the rate of 526 kg/ha applied at planting; T4-organic fertilizer at 8 ton/ha rate + Trichoderma spp. at the rate of 526 kg/ha, both applied twice (at planting and 30 DAT); T5-organic fertilizer at 8 ton/ha rate applied twice (at planting and 30 DAT) + Trichoderma spp. at the rate of 526 kg/ha applied thrice (at planting, 30 DAT and during bulb formation). Results of the study showed that application of the recommended rate of organic fertilizer twice (at planting and 30 DAT) + three times application of Trichoderma spp. (at planting, 30 DAT and during bulb formation) consistently produced bigger bulb during the first and second trial of the study, compared to other treatments evaluated. Consequently, higher marketable yield was produced with 15.33 ton/ha during the first trial and 14.50 ton/ha on the second trial.