Plant substrate and use thereof

A plant substrate, comprising 20 to 100% of a granulate selected from the group consisting of foamed clays, slightly fired ceramic materials and mixtures thereof, the granulate being sprayed with a solution of an active substance selected from the group consisting of nutrients, fertilizers, pesticides and combinations of these, and then covered with a covering solution which first hardens but then loosens up under the action of water, root juices or both, wherein the covering solution is a waterglass solution that has previously been reacted with lime, chalk or gypsum.