<P> Hydroponics is a subset of hydroculture, the method of growing plants without soil, using mineral nutrient solutions in a water solvent . Terrestrial plants may be grown with only their roots exposed to the mineral solution, or the roots may be supported by an inert medium, such as perlite or gravel . The nutrients in hydroponics can come from an array of different sources; these can include but are not limited to byproduct from fish waste, duck manure, or normal nutrients . </P> <P> The earliest published work on growing terrestrial plants without soil was the 1627 book Sylva Sylvarum or A Natural History by Francis Bacon, printed a year after his death . Water culture became a popular research technique after that . In 1699, John Woodward published his water culture experiments with spearmint . He found that plants in less - pure water sources grew better than plants in distilled water . By 1842, a list of nine elements believed to be essential for plant growth had been compiled, and the discoveries of German botanists Julius von Sachs and Wilhelm Knop, in the years 1859--1875, resulted in a development of the technique of soilless cultivation . Growth of terrestrial plants without soil in mineral nutrient solutions was called solution culture . It quickly became a standard research and teaching technique and is still widely used . Solution culture is, now considered, a type of hydroponics where there is no inert medium . </P>

Hydroponics is a technique in which plants are grown in