Epsom salt is magnesium sulfate. It is a naturally occurring chemical compound meaning it can be used in organic gardening. It is magnesium and sulfur which means it not only lowers the pH of the soil, it also provides essential magnesium which helps to green plants and works with soil Nitrogen to green the plant and boost plant health. It can also be used to soothe sore muscles after a long day in the garden and then still used on your plants!