The development of oil palm on peatlands presents significant problems and challenges. The prolonged process of oil palm cultivation, accompanied by the continuous use of chemical fertilizers and pesticides, puts the land at risk of degradation. Land degradation indeed risks reducing productivity, especially on land that has been infected with Ganoderma boninense. The problem is increasingly complex and challenging to solve. The use of biological agents and ameliorants to enhance productivity on degraded land should be implemented. This study aimed to evaluate the effectiveness of applying potential bacteria as biofertilizers and biocontrols, along with ameliorants, on improving soil fertility and the growth of oil palm seedlings in peat media infected with G. boninense. Therefore, in this study, an effectiveness test was carried out on the application of ameliorants (biochar from palm shell (A1); ash from oil palm empty bunch (A2); and cocopeat (A3)) and potential bacteria that play a role as biocontrol biofertilizers (S2A, H5, and F2 isolates). This study employed a completely randomized design with three replicates, conducted in a greenhouse on 2-month-old DxP oil palm seedlings planted in hemic peat without dolomite. The application of ameliorants and bacteria that act as biocontrol biofertilizers in G. boninense-infected peat media influences soil chemistry and oil palm seedling growth. S2A isolates show the best adaptation in growth in propagation media, while H5 and F2 isolates show similar growth trends. Ash is the best treatment on its own in terms of soil pH parameters and leaf count. The best interaction between the ameliorant and bacteria was observed in the combination of ash (A2) and S2A (B1) isolate, which affected the parameters of total Nitrogen (N), available Phosphorus (P), and total Potassium (K) in the soil, as well as plant height and root length of oil palm seedlings after 10 weeks of application. The use of ameliorants and bacteria as biofertilizers and biocontrol agents can be a way to address soil fertility issues and soil-borne diseases, particularly in oil palm plantations on peatlands.