Hydroponics is a technique for growing plants without soil. It uses an inert medium (peat, sand, vermiculite, etc) to which a solution is added containing all the essential nutrients required for normal plant growth. A purer form of hydroponics, water culture, involves growing plant roots in water containing nutrients. Their crowns are supported in a thin layer of inert medium. Hydroponics is also known as 'soilless culture'.
Hydroponic techniques are well suited to roof gardens. The advantages are:
Soil is a growing medium, but it is not a necessary one. Inert substances like perlite or vermiculite can also serve as growing mediums (as they do in hydroponics). What is necessary are the nutrients the soil or perlite contains. In hydroponic systems, a specially formulated, nutrient rich solution, containing all the necessary macro- and micronutrients necessary for healthy plants, is pumped through an inert medium. The systems are typically installed in a greenhouse or other controlled environment so that it can be carefully monitored. Hydroponics is considered a science and is highly specialized, but can, however, be successfully practiced by hobbyists.