The effect of silicon on growth of French marigold seedlings ‘Boy Orange’ and ‘Yellow Boy’ was investigated. Seeds were sown in the foam wedge trays and placed in an environment controlled chamber (25 ± 1°C, 80% RH, dark) for three days. A nutrient solution containing 0, 25, 50 or 100 mg l^-1 silicon was supplied uniformly twice a day after seed germination. The seedlings were maintained at 25 ± 2°C under a 12 h photoperiod with 430 µmol m^-2 s^-1 irradiance and 60% relative humidity. In both cultivars, addition of silicon significantly increased stem diameter, number of lateral shoots, root length, chlorophyll content, and fresh and dry weights, as compared with the control. No significant difference in plant height was observed in all treatments; however, supplementation of silicon led to decrease in plant height when compared with the control. In ‘Boy Orange’ increase in silicon concentration from 25 to 100 mg l^-1 resulted in a significant increase in root grade, while in ‘Yellow Boy’ no significant difference was observed. The optimal concentration of silicon varied among the cultivars. The highest biomass, chlorophyll content and number of lateral shoots were obtained in ‘Boy Orange’ and ‘Yellow Boy’ when 100 and 25 mg l^-1 silicon was supplied, respectively. Molybdenum blue method confirmed the presence of silicon in leaves of both cultivars. Our data suggested that silicon may improve the growth of marigold cultivars under unstressed conditions.