Why?..................well, some advantages include:
1. Controlled environments enhance speed to maturity and increase yields.
2.Water 'consumption' is reduced, as there is no independent watering process, so none is lost due to evaporation (other than plant evapotranspiration) or capillary action in the soil. Water is recycled in the system.
3.Flower and fruit quality can be improved, there are no soil born pests and deseases to eliminate, and no soil to remove from the plant. Plants are protected from insects, and predators can be used in the greenhouse.
4. Plants can be moved easily, labour costs are low, and minimal 'potting on' is needed.
5. Artficial lighting can be used in dark areas (although of course energy consumption must be considered), and the method is ideal for 'clean' areas such as conservatories or swimming pools.
All of the above have to be balanced against the inital capital costs, nutrient and heating costs, and control systems. This means that the home gardener is unlikely to make a sytem pay for itself, but it is still an interesting hobby.
I think of Hydroponics as being a scientific method for growing plants. The idea is that you analyse exactly what is needed for a plant to grow, then you arrange to supply it in carefully delivered and controlled quantities. Most gardeners know that there are always three fundamental chemicals involved, the famous N-P-K element trilogy (nitrogen, phosphorous, potassium), in addition to water, heat and sunlight. These basic elements have to be available in the forms (compounds) that can be absorbed by the roots (and possibly the leaves) of the plants. To really understand what is happening, you also need to understand how roots take in their nutrients. This is dependent on the pH ( a logarithmic scale used to indicate the level of acidity/alkalinity) of the available water in the soil. It is very complicated, and I do not have the necessary education to understand it, but there is a huge amount of information available for those who would like to study. However, you can find plenty of information to establish a hydroponic process. perhaps the best place to start is at one of the many professional sellers or gardens. I have visited the Hampshire Hydroponicum at Houghton Lodge Gardens (www.houghtonlodge.co.uk). This is a great place to learn more, and they have their own publications to help. I picked up a nice leaflet of FAQ's that really helps.
The nutrient requirement includes 'trace' elements. These are present at very low concentrations, yet are vital to plant growth. They include calcium, magnesium,sulphur,iron,boron, manganese, zinc copper and molybdenum. Plants are propagated in non-organic materials such as Perlite, Rockwool,Vermiculite and sand or gravel.