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Hydroponics

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).

Table of contents

1 Techniques 1.1 Passive hydroponics 1.2 Flood and Drain (or Ebb and Flow) 1.3 Drip feeding 1.4 Raft cultivation 1.5 Nutrient Film Technique (NFT) 1.6 Aeroponics 2 Media 2.7 Clay Pebbles 2.8 Rockwool 2.9 Coco Coir 3 Present and future

Techniques

Passive hydroponics

Flood and Drain (or Ebb and Flow)

In its simplest form, there is a tray above a reservoir of nutrient solution. The tray is either filled with growing medium (clay granules being the most common) and planted directly, or pots of medium stand in the tray. At regular intervals, a simple timer causes a pump to fill the upper tray with nutrient, after which the nutrient drains back down into the reservoir. This keeps the medium regularly flushed with nutrient and air.

Drip feeding

Similar to Flood and Drain in its physical setup, except the pump delivers a continuous trickle of nutrient onto the medium.

Raft cultivation

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.

Nutrient Film Technique (NFT)

In this method, the plants grow through light-proof plastic films placed over shallow, gently sloping channels. A steady flow of nutrients is maintained along the channel, and the roots grow into dense mats, with a thin film of nutrient passing over them (hence the name of the technique). A downside of the technique is that it has very little buffering against interruptions in the flow e.g. power outages, but overall, it is probably one of the more productive techniques.

Aeroponics

Media

Clay Pebbles

Rockwool

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.

Coco Coir

Present and future

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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