The basic types of hydroponic systems are: Wick, Water Culture, Flood & Drain, Drip (recycling or non-recycling), NFT, and Aeroponic.
There are numerous variations on the basic types listed above, but all of these varaiations contain features of one (possibly 2 or 3) of these basic types.
The wick system is the most basic of the six types, utilizing a passive irrigation method meaning it has no moving parts. The nutirent solution is simply drawn into the growing medium via a wick. This system like the water culture, flood & drain, and drip method all can use a variety of growing medium. Perlite, vermiculite, and coconut fibers are some of the most popular. The biggest problem with this type is that the wick can dry out. If this happens then the plants also dry out. Dry wicks are usually the result of the plants using water faster than the wick can deliver it, especially in high heat.
The water culture method is the oldest and simplest of the basic methods of hydroponic growing. This method dates back to the days of the Azteks who grew floating gardens in the ponds around their temples. In this type plants are grown in floating platforms typically made from Styrofoamh which are then floated in the oxygenated (via an airstone connected to an air pump) nutrient solution. Lettuce, a water loving plant is ideally suited to this type of set up. The water culture method is also often the type that is used in classrooms as an educational tool due to its low cost.
The flood and drain method is as it name suggests, method that floods the container that the plants are growing in and then drains it in order to deliver the nutrient solution to the plants. The way it works is there are to containers one on top of the other with the bottom container being filled with the nutrient solution. In the top container is filled with a growing medium in which the plants are placed directly. the nutrient solution is then pumped up to the top container when a submersible pump is turned on and drained back out via the same tube when the pump is switched off. An overflow tube is also installed in the top container to ensure that no water is lost. A variety of vegetables can be grown with this method, however if the power supply for the pump is unterrupted for to long the plants roots may dry out and kill the plants. To alleviate this problem a more absorbant grow medium should be used such as vermiculite or coconut husk.
The most common type of hydroponic system in use today is the drip system. The set up is pretty basic. There is a timer that controls a submersible pump which turns on at regular intervals to deliver the nutient solution to the base of each plant via a drip line.
Drip systems can be either recovery or non-recovery. In a recovery system the nutient solution is collected in a resevoir and then recycled back to the plant. this is the more efficient of the two as more of the nutients are use before being lost as run off. It also allows the gardener to us a less expensive timer to control the watering cycles. In a non-recovery system the nutirent solution is not collected and recycled and there for is lost once it passes through the system. timers that allow for very short intervals (1 minute) are required to minimize the loss of the nutrient solution. these timers are usually more expensive.
NFT (Nutient Film Technique) systems are the kind of hydroponic system that usually is first to jump to mind when people start talking about hydroponics. This method doesnt require a timer as the nutirent solution is constantly pumped into the root chamber. Once in the root chamber (growing tray) it simply flows past the roots and is routed back into the resevoir to be recycled. The roots of the plants typically hang in the air as the water flows past, however to safeguard against the roots drying out in the event of a power outage, an absorbent medium such as capillary mat or even old newspapers can be placed in the bottom of the growing tray.
The aeroponic system is probably the most high-tech type of hydroponic gardening. Like the N.F.T. system above the growing medium is primarily air. The roots hang in the air and are misted with nutrient solution. The mistings are usually done every few minutes. Because the roots are exposed to the air like the N.F.T. system, the roots will dry out rapidly if the misting cycles are interrupted.
A timer controls the nutrient pump much like other types of hydroponic systems, except the aeroponic system needs a short cycle timer that runs the pump for a few seconds every couple of minutes.