There are a variety of techniques employed in hydroponics.
Some, while dispensing with soil, use relatively inert material as a physical support for the plant roots. Other techniques dispense altogether with any growing medium, delivering nutrient solution directly to the roots by a variety of methods.
The simplest method: the plant is planted in a container (pot or bag) of growing medium, and the container stands in a tray of nutrient solution. The medium generally has large air spaces, allowing ample oxygen to the roots, while capillary action delivers water and nutrients to the roots. A variety of materials can be used for the medium: vermiculite, perlite, clay granules, rockwool, gravel, Oasis Horticubes. Some newer media that are becoming popular are coir fibre, and cocoa bean shells. This needs the least maintenance of all hydroponic methods, requiring only topup and occasional replacement of the nutrient solution.This keeps the medium regularly flushed with nutrient and air. It is important in passive hydroponics to wash out the system from time to time to remove salt build up. This may be checked with a PPM meter, a good average reading would be about 1500 PPM. Lettuce grows well at about 800 PPM and tomatoes to 3000 PPM but both will grow reasonably well on 1500 PPM. It is important to keep the pH reading at about 6.3 to enable nutrient uptake. Data are available for the optimum settings for most plants. This is commonly employed for large display plants in public buildings: in Europe a system using small clay granules is marketed for growing houseplants.
Passive hydroponic at home – Semi-hydroponic for growing orchids
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.
Deep Water Culture (DWC)
Deep Water Culture is a hydroponic method of growing plants in which the roots are suspended above, and allowed to drop down into an aerated nutrient solution. This is not natural but with a properly aerated solution the roots can be continualy submerged without problems because the roots take up nutrients in the presence of oxygen. The solution is usually aerated constantly by using standard aquarium pumps and air stones, which deliver oxygen to the roots. The container holding the roots and aerated nutrient solution must be completely light proof in order to prevent algae growth. The solution must be topped up from time to time.
Similar to Flood and Drain in its physical setup, except the pump delivers a continuous trickle of nutrients and water onto the medium. The emitters are commonly set to run 5 to 10 minutes every hour.
A variation on Drip feeding, except that the plant draws water by means of a wick. The wick runs from the base of the plant container (e.g. a pot or a tray) down to a bottle of nutrient feed solution. The solution travels up the wick into the plant through capillary action.
A variant of DWC 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.
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.
A class of hydroponics where the roots of a plant are suspended in a mist or fog of nutrient rich solution. Traditional aeroponic techniques use pumps and misters more commonly found in micro-irrigation systems, whereas state-of-the-art techniques employ ultrasonic nebulizers which render the nutrient solution into an extremely fine fog. See: Homemade aeroponics for free plans.
For more indoor,outdoor, and hydroponics information, please visit San Diego Hydroponics & Organics website.