Different K/(Ca+Mg) ratios in complete nutrient solutions were supplied at vegetative and flowering stages to optimize their critical levels for high-quality performance of chrysanthemum (Dendranthema grandiflorum Ramat. cv. "White Zamble") grown on mixture medium (peat moss: perlite, 2:1 v/v) under fertigation system. The treatments consisted of three ratios of 0.33, 0.55 and 0.71, were performed every 3 days at a constant volume of all nutrient solutions (300 ml/pot) during each growth season (28 weeks). A ratio of 0.71 proved to be optimal for chrysanthemum cultivation since it appeared to have the best results of vegetative characters (plant height, number of shoots and leaves per plant, leaf area, dry weights of roots and shoots, root/shoot ratio and relative growth rate), as well as inflorescence characters (days to flower, yield, fresh weight and stalk length). This ratio also followed the same pattern in relation to leaf pigments content and total carbohydrates, but this behavior was in direct contrast with flavonoids level. Although a ratio of 0.33 showed inferior results in growth and flowering, it was superior in flavonoids synthesis in leaves. The performance of a ratio of 0.55 was intermediate. The cationic ratios had an insignificant effect on phenolic compounds.