The invention relates to compositions for retaining soil moisture and improving plant growth in dry soils, which, together with one or more moisture retaining materials and wetting agents, comprises iron(III) oxides and optionally potassium metabisulfite [borken (HU), E224] as potentiating agent. The iron(III) oxides preferably are microparticulate. The composition Suitably comprises iron(III)oxides and potassium metabisulfite as potentiating agent. Other aspects of the invention relate to binding the moisture content of soils, as well as compositions for use in enhancing the efficacy of Soil retaining compositions.