Silicone (Si), a very abundant element in the Earth’s crust, is beneficial for plants, animals and humans. Despite its abundance in nature, it is often unavailable in sufficient quantities. Cucurbits are believed to accumulate elevated quantities of Si and benefit from Si fertilization. It is believed that higher Si content in cucumber plant is connected with increased yields as well as improved resistance to diseases and tolerance to abiotic stresses, for example drought. The beneficial effects of Si have been confirmed by the present study, in which cucumbers were grown in soil and in liquid nutrient solutions. The aim of the experiments has been to evaluate the effect of several silicates supplementing peatbased growing substrates on yield and Si content in growing media and in cucumber plants. For this purpose, pot experiments were carried out in an unheated greenhouse in 2005- 2007. Cucumber plants were cultivated in 12-liter containers filled with substrates amended with Na-, K-, Ca- and ammonium silicates at rates of 2 or 4 g per liter. The results indicated that slow-release Ca- and NH4-silicates contributed to increased yield and elevated Si content in cucumber leaves and fruits. The effect of the other silicates was not certain and, additionally, dependent on their concentrations. Water-soluble Na- and K-silicates caused increased Na or K concentration and raised pH of substrates. The results revealed that increased yields depended on the number of fruits rather than their average weight. The silicates of calcium and ammonium can be valuable, slow-release fertilizers in cucumber cultivation on organic (peat) substrates. Even in quantities as high as 4 g per liter of substrate, they did not cause drastic changes of the pH and salinity of growing media and were a good source of Si available to cucumber plants.