Hydroponics is the growing of plants without soil. A variety of techniques exist.
Researchers of plant metabolism have discovered that plants absorb nutrients as simple inorganic ions in water. In natural conditions, soil acts as a nutrient reservoir but the soil itself is not essential to plant growth. When the nutrients in the soil dissolve in water, plant roots are able to absorb them. When the required nutrients are introduced into a plant's water supply artificially, soil is no longer required for the plant to thrive.
Hydroponics is useful to us in two main ways. First, it provides a more controlled environment for plant growth than soil thereby removing many unknowns from experiments. Second, many plant species produce more product in less time and sometimes of higher quality, which under certain economic and environmental conditions, makes hydroponic growing more profitable to the farmer.
The first researcher of hydroponics was John Woodward of England, who, in 1699, grew plants in water to which he had added various soils. This demonstrated that the earth contained various substances which the plants needed besides water. In the mid-19th century, the German plant physiologists Sachs and Knop grew plants in simple solutions of inorganic salts.
In 1929, Professor Gericke of the University of California, Los Angeles demonstrated that plants could be grown soil-free all the way to maturity, growing tomato plants in water to a quite remarkable size. By analogy with the ancient Greek term for agriculture, geoponics, the science of cultivating the earth, Gericke coined the name hydroponics for the culture of plants in water (from the Greek hydros, water, and ponos, labour).
Sometimes used for lettuces: sheets of expanded polystyrene have holes drilled through them, and young plants are placed in the holes with the roots hanging down. The sheet then floats in a shallow tank of nutrient solution. The tank is kept aerated by an air pump to ensure the roots have adequate oxygen.
Rockwool gets its name from its physical properties: it is, in fact, pieces of basalt rock that have been spun out to form a wooly substrate. This 'wool' is then compressed into blocks. Before use, rockwool must be soaked in pH 5-6 water with a cF of 12 (cF stands for 'conductivity factor', which is, put simply, the amount of nutrient in the water. If you do not have a cF meter, just follow the formula on the back of the packet and you will be fine) for a few minutes. The rockwool should then be removed and squeezed slightly to remove approximately 10 per cent of its water. Rockwool can be bought in 'cuttings cubes', cubes that are good for inserting cuttings into, 'transplantation cubes', which are for inserting cuttings cubes into and then placing into a larger system, as large slabs, or as very small 1cm cubes, which are used in place of clay pebbles or some other medium. These tiny cubes are known as 'Cellmax', but are still rockwool. Note that fibres of rockwool can break off and lodge in a user's lungs, causing irritation, so care must be taken.
Rockwool exhibits a behavior called 'conditioning' in which it gradually absorbs phosphorus. New rockwool usually has a pH around 7.4 - 7.6. The absorbed phosphorus is available to plants, but is removed from the nutrient solution. Over time as the phosphorus builds up, the rockwool becomes 'conditioned' and absorbs progressively smaller quantites of phosphorus until it becomes saturated. This process is beneficial to flowering plants because the rockwool serves as a storage for the large quantities of phosporus needed during flowering. Providing large amounts in the nutrient solution could cause nutrient burn and excessively low pH, which in turn would lock out other nutrients.
Hydroponics can be used to grow plants anywhere, from Antarctica (where salad vegetables are grown in the 6 month nights) to a coal mine. When vegetables are grown in future space missions, it is likely to be by hydroponic methods. The fact that plants can be grown almost anywhere, with no natural light by using hydroponics and lighting has not escaped the notice of clandestine marijuana growers, and a large amount of hydroponics equipment appears to be in use for this purpose. In the UK, theft of high intensity grow lamps from commercial vegetable growers is a chronic problem. Wide availability and low cost of equipment in the U.S. makes theft from greenhouses a rare event.
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