Silicon is known as an element stimulating plant immunity and resistance to unfavorable conditions. Additional treatment with silicon may also cause a positive change in plant performance, improving the quality of ornamental plants. In the years 2009-2010, a two-factorial experiment was conducted involving three cultivars of seasonal ornamental plant species: creeping zinnia <i>Sanvitalia speciosa</i> 'Sunbini', vervain <i>Verbena</i> 'Patio Blue', and purslane <i>Portulaca umbraticola</i> 'Duna Red'. The first experimental factor was the concentration of Actisil preparation being an equivalent of 60, 120, and 180 mg Si×dm^-3, applied three times by spraying, the second one was the type of medium: peat substrate and peat substrate with sand. The experiment proved the beneficial effect of fertilization with silicon on plant development of <i>Verbena</i> and the number of shoots of all examined plant species. The higher concentrations of Actisil were applied, the higher number of shoots the plants developed. Plants treated with Actisil also produced a higher number of buds and flowers or inflorescences featuring an increased diameter. Plants cultivated in peat substrate flowered better.