Hydroponics is a system of growing plants without soil. The plants are typically grown in nutrient solutions of water and fertilizer. A hydroponic system may grow in an artificial medium to provide mechanical support, such as sand, gravel, vermiculite or sawdust, or the roots may be left with no mechanical support.
The Romans developed the first greenhouses, in which they grew cucumbers during winter months for the emperor under "transparent stone." Workers in U.S. Agricultural stations conceived of the first true hydroponic systems for growing food in 1925. These workers had to frequently change the soil of these greenhouses as nutrients were depleted.
According to the University of Arizona, although hydroponics is a more expensive way of growing food, it produces higher yields of crops that are healthier because they are not exposed to the bacteria and fungus present in soils. Additionally, these crops contain more nutrients because they are exposed to and absorb more nutrients at the roots than crops that are grown in soil. Because of this, hydroponics is a promising technology for growing plants in places where soil is poor.
Hydroponic plants are started from seedlings in a soilless mixture such as peat moss or rockwool blocks. Once the seedlings emerge, the blocks are placed in larger growing cubes. As the root system develops, these cubes may be placed inside larger growing cubes in a "pot-in-pot" system of growing several different times. The roots of the plants are never confined and never allowed to touch one another. If the roots touch at all, the plant is considered to be overcrowded.
If the plants become leggy from being overcrowded, their blocks may be transplanted in a specific process. The block is turned upside down and the plant's stem is bent into a U shape. The plant will grow new roots from the parts of the stem that are underneath the peat while the plant becomes stronger and healthier. This process works especially well with tomato vines.
The spacing of hydroponic plants may be much denser than in soil. A space as small as 2 square feet has been used for the root system of tomato plants without the plants experiencing overcrowding. The spacing of plants is a function of sunlight. The more sunlight a plant receives the more compact the root system will be. Plants that are grown in lower lighting conditions spread their root systems out further.