In June 2007 we have added at the end of this section a very good paper which describes 'Plastics that kill plants' - we thank the Authors.
Excerpts and comments from the books
‘Hydroponic Gardening’ and ‘Hydroponic Crop Production’
The history of hydroponic growing:
The term hydroponics was coined in the USA in the early 1930's to describe the growing of plants with their roots suspended in water containing mineral nutrients. Derived from the Greek words for 'water'— hydro and 'to work'— ponos, hydroponics literally means 'working with water'. The definition has gradually become broadened to describe all forms of gardening without soil.
Hydroponic gardens in history date back to the Hanging Gardens of Babylon. The Aztec Indians had a system of growing crops on rafts in shallow lakes, you can still see some of these floating gardens near Mexico city. Developments did not start taking place in Europe until 1699 when Woodward found that he could grow plants in a solution of water to which soil had been added. Liebig, a German scientist, started using nutrient solutions to study the nutritional requirements of plants in the 1850's and was followed by Sachs in 1860 and Knop in 1861 who made studies of nutrient elements in water solutions. They were able to grow plants in nutrient solutions made up from mineral salts eliminating the need for soil.
Research on the nutritional requirements of plants continued through into the 1870's. By 1925 practical applications of hydroponics were being made in the greenhouse industry. The next decade was to see extensive development as researchers became aware of the potential of growing hydroponically. In 1930 Gericke produced the first commercial hydroponic unit in the USA Later during World War II the American forces in the Pacific grew vegetable crops hydroponically. Developments continued and the commercial use of hydroponics spread throughout the world but it was the development of a system known as N.F.T. by Dr Allen Cooper in the 1970's, along with improved nutritional formulations that made the hydroponic growing of a wide range of plants commercially viable. Since then automatic control systems have become available as well as digital testing equipment which has really opened up the field of hydroponics to the home gardener.
How Hydroponics can work for you
Hydroponics is no longer a subject of science fiction or a mysterious form of growing plants in a laboratory. It is a well established and fast growing part of modern commercial agriculture. Anyone willing to familiarize themselves with the principles of hydroponic culture and the basic requirements of planing and caring for a garden can successfully establish and operate a highly productive and rewarding hydroponics unit. Hydroponics is still a developing field so you will find plenty of range for experimenting, with plants and even trees.
Advantages of hydroponic culture
In areas of the world where good growing soils are not available, hydroponics can allow for good crops. Rocky or poor soil composition are two examples.
Digging and weeding are a thing of the past. Since there is no competition for nutrients and water a much higher density of planting can be made.
As soon as a mature plant has been harvested it can be replaced with a new one, meaning that the hydroponic system is extremely cost effective - compare this with normal soil growing and the time which has to be allowed between crops.
Because provision of the best nutritional conditions are relatively easy in hydroponics, then the potential to produce top yields is vastly increased.
Because the plants in a properly managed hydroponic system tend to grow quicker and are generally healthier, they generally do not suffer as much from any attack from pests and plant diseases, resulting in higher quality crops, full of flavour and with good texture.
In the past it was sometimes difficult to get good advice on hydroponic growing techniques and system design. Today there are a number of companies around the world that now have years of experience and many are only too pleased to assist you with the smallest of problems. (See our page of hydroponic links)
Hydroponic growing systems:
There are two basic methods of hydroponic growing. The traditional method was to hold the plants roots in an inert media. An ideal media will not add any chemical matter to the nutrient - in other words it must be inert. It should provide good drainage and thereby aeration (oxygen to the root zone) It should retain some moisture.
Typical media's are:
Coarse washed river sand - Gravel - Scoria - Vermiculite - Crushed rock - Perlite
Expanded clay (Hydroton) - Composted bark and some untreated sawdust.
The other common method of hydroponic growing is carried out using gully’s. This system is termed nutrient film technique (NFT) where the base of the root mat is in contact with flowing, oxygenated nutrient and the plants absorb nutrients and water via capillary action. Other methods are the deep flow technique and the raft system where the plants are suspended in tanks and gully’s which are filled with nutrient - these methods which see the roots totally submerged into the nutrient, rely solely upon the dissolved oxygen in the nutrient to keep the root mat in healthy condition.
The nutrient is obviously the very basis of hydroponic growing and it must be correct for the job it is expected to do. The nutrient is made up of thirteen different mineral elements and they must all be included, otherwise the health and operation of the plant will be unsatisfactory. These elements are grouped into ‘Major or Macro elements’ and ‘Minor or trace elements’
The major elements are: Nitrogen - Phosphorus - Potassium - Calcium - Magnesium -and Sulphur and the minor elements are Iron - Boron - Manganese - Copper - Zinc - Chloride and Molybdenum.
Obviously there is a wide range of formulations available and many hydroponic growers have also formulated their own favourite brew(see the Vitaran HC hydroponic nutrient calculator elsewhere in this site). The main points to know are that all the constituents in the formula must be 100% soluble in water otherwise the plants cannot absorb them. That Nitrates and sulphates should not be mixed together in their concentrated form otherwise a chemical precipitation will take place - this is why most nutrient concentrates, whether they be liquid or powder are supplied in two separate containers. Finally formulas should be constructed within the limits of the figures shown here
Sufficient Chloride and minuscule additions of other rare elements are almost always provided either from within the water supply or as an impurity constituent among the other raw materials.
Plants require very small quantities of some elements and one of the problems for the unwary in hydroponic growing is the poisoning of the plants by having ‘toxic’ levels of some elements in the nutrient - this can be caused by poor weighing (measuring) of the raw materials, or by using the incorrect raw materials or by exposing the nutrient to toxic metals and minerals. Ensure that all components likely to come into contact with the nutrient solution are inert i.e. They should be stainless steel, glass or non toxic plastic.
It is important to apply the ideal strength of nutrient to your plants - different plants will require different strengths for optimum growth. This is achieved by measuring the electrical conductivity of the nutrient solution - either meters which simply display the measured value or controllers that can be set to maintain a desired value will assist in attaining optimum growth conditions. Measurement by TDS or PPM should be avoided as being too inaccurate for consistent performance
Hydroponic nutrient pH value:
The other value which should be controlled in order to obtain maximum performance is the pH (acidity or alkalinity) of the nutrient solution. This value can be measured with a pH tape (colormetric system) or with a pH meter such as the ‘pH Wand’ or a digital pH meter. The general tendency is for pH to rise during plant growth and the pH is dropped down again using Phosphoric acid. During low light periods the pH may fall during plant growth and should be returned to the ideal range of between 5.8pH and 6.5pH by the use of Potassium hydroxide (caustic potash)
Hydroponic nutrient growing strength:
As a guide, we reprint here the ‘nutrient strength’ chart from the book ‘Hydroponic Gardening.
Note that 1 CF unit is = to 0.1 EC and although there are several interpretations of the relativity of ppm to conductivity measurement the value of 70 ppm per CF unit is widely accepted around the world. Therefore a reading of 20CF would equal 1400 ppm.
Also note that the values given above are from the 'hobby' book Hydroponic Gardening and these values will be a good guide when growing at home - Conversely, many commercial cultivars grow at very much higher levels - e.g. some Hybrid tomato varieties are grown in excess of 100CF (10EC)
We hope that the above information will assist you - for more in depth discussion of the subject we suggest you read the book ‘Hydroponic Gardening - A guide to growing plants without soil. If you then decide that a larger system or even a commercial hydroponic growing enterprise is for you, then the book ‘Hydroponic Crop Production’ has been written especially for you. For more information see our page on Hydroponic books!