Epsom salt helps improve flower blooming and enhances a plant's green color. It can even help plants grow bushier. Epsom salt is made up of hydrated magnesium sulfate (magnesium and sulfur), which is important to healthy plant growth. Rock phosphate, or phosphorite, is mined from clay deposits that contain phosphorus and is used to make organic phosphate fertilizers that many gardeners utilize Phosphate rock is, of course, an essential source of phosphorus – the essential nutrient ‘P’ from the three vital nutrients “NPK.” It’s used for making organic phosphate fertilizers for gardens.