Compositions for application to a soil for retaining water in the soil for plants are prepared by applying an aqueous solution containing sodium and/or potassium methylsiliconate to a substrate so that the siliconate applied is in an amount of between 180 g and 1,000 g per m.sup.3 substrate and then, the treated substrate is allowed to dry at ambient temperature. The substrates employed include tree bark, sawdust, compost and vegetable mould and also gravel and sand. Additionally, porous articles prepared for containing plants also may be treated for improving retention of water.