A field experiment was conducted during 2014 to study the effect of different methods and times of application of fertilizers of Mg and B on growth and yield of yard long bean and soil characteristics of southern laterites of Kerala. The experiment was laid out in Randomized Block Design with ten treatments and three replications. The results indicated that the application of Mg and B reduce the number of days to flower and increase number of harvests and productive duration. The highest leaf area (1.82 m2), total dry matter production (2700 kg ha-1) and yield (10052 kg ha-1) were recorded by the treatment which received foliar application of 2% magnesium sulphate and 0.25% borax at fortnightly intervals + soil test based package of practices recommendations (T9). Maximum apparent recovery efficiency of Mg (89.5%) and B (2.90%) noticed in T7 (foliar application of 2% magnesium sulphate and 0.25% borax at first flowering). The highest benefit cost ratio (2.27) was registered by the treatment which received foliar application of 2% magnesium sulphate and 0.25% borax twice at first flowering and active flowering (T8).