The oil palm industry is significantly affected by basal stem rot (BSR) caused by Ganoderma boninense. Nutrients are frequently used in soil fertilisers to protect plants from various stresses. Manipulating plant nutrients, particularly calcium (Ca), offers a promising strategy to prevent BSR disease in oil palm. This study evaluates the effect of Ca-based formulations on the suppression of G. boninense infection in oil palm seedlings using the root-sitting technique in three-month old oil palm seedlings. The study was further conducted in the field to test the disease incidence of BSR using the seedling baiting technique. Oil palm seedlings were pre-treated with fertiliser containing 1,000 ppm Ca as CaSO₄. They were then exposed to G. boninense PER 17 using two methods; in a 12-month nursery trial, colonised rubber woodblocks were attached with seedling roots to simulate infection, while in a 21-month field trial, seedlings were planted in soil naturally infested with the fungus to test real-world conditions. In both trials, fertiliser with 1,000 ppm Ca reduced BSR incidence by 53% in the nursery and 81% in the field. This suggests Ca supplementation as an effective alternative for preventing BSR in oil palm plantations.