Tropica Nutrition Capsules are a safe and convenient method of provide nutrients to the roots of your plants. They contain Nitrogen, Phosphor, Iron and Manganese, as well as all vital micro-nutrients, these are released by the capsules over a period of 1-2 months. The capsules do not fully decompose and the small balls inside the capsules will remain in the substrate after all nutrients have been released. The balls are made of resin, which is biologically harmless.