Experiments were laid out in cardamom plantations of Idukki district to optimize the dosage of magnesium and boron. The trials for the optimization of Mg and B dosage were conducted separately. For Mg, treatments imposed include soil application of five doses of MgSO₄ @ 20, 40, 60, 80, 120 kg ha^-1 and a control (without Mg source). In the case of B, treatments imposed include soil application of B @ 0.5, 1, 1.5, 2.0 kg ha^-1, and foliar application of borax @ 0.2 % and control treatment without the application of B source. Magnesium and boron treatments were imposed separately on cardamom plants which showed the deficiency symptoms of corresponding nutrient. In Mg trial, the highest cardamom yield, highest nutrient content in index leaf and highest availability of secondary and micronutrient in the soil were obtained from the treatment which received MgSO₄ @ 120 kg ha^-1. Similarly for B trial, highest cardamom yield, highest nutrient content in index leaf and highest availability of secondary and micronutrient in the soil were obtained from treatment which received foliar application of borax @ 0.2 %. Critical level of Mg and B in the index leaf of cardamom was found to be 0.31 % and 16 mg kg^-1, respectively. The critical limit of available Mg and B content in soil was delineated as 160 and 4 mg kg^-1, respectively.