Hydroponic Systems

Hydroponic Systems
Hydroponic systems are characterized as active or passive. An active hydroponic system actively moves the nutrient solution, usually using a pump. Passive hydroponic systems rely on the capillary action of the growing medium or a wick. The nutrient solution is absorbed by the medium or the wick and passed along to the roots. Passive systems are usually too wet and do not supply enough oxygen to the root system for optimum growth rates.

Hydroponic systems can also be characterized as recovery or non-recovery. Recovery systems or recirculating systems reuse the nutrient solution. Non-recovery means just what it says. The nutrient solution is applied to the growing medium and not recovered.
 
The Ebb and Flow System
The Ebb and Flow hydroponic system is an active recovery type system. The Ebb and Flow uses a submersible pump in the reservoir and the plants are in the upper tray. They work on a simple flood and drain theory. The reservoir holds the nutrient solution and the pump. When the pump turns on, the nutrient solution is pumped up to the upper tray and delivered to the root system of the plants. The pump should remain on for about 20 to 30 minutes, which is called a flood cycle. Once the water has reached a set level, an overflow pipe or fitting allows the nutrient solution to drain back into the reservoir. The pump remains on for the entire flood cycle. After the flood cycle the nutrient solution slowly drains back down into the reservoir through the pump.

During the flood cycle oxygen poor air is pushed out of the root system by the upward moving nutrient solution. As the nutrient solution drains back into the reservoir, oxygen rich air is pulled into the growing medium. This allows the roots ample oxygen to maximize their nutrient intake. Rockwool and grow rocks are most commonly used growing mediums in Ebb and Flow type systems. The Ebb and Flow is low maintenance, yet highly effective type of hydroponic gardening.
 
The Wick System
The wick system is a passive non-recovery type hydroponic system. It uses no pumps and has no moving parts. The nutrients are stored in the reservoir and moved into the root system by capillary action often using a candle or lantern wick. In simpler terms, the nutrient solution travels up the wick and into the root system of the plant. Wick systems often uses sand or perlite, vermiculite mix and a growing medium. The wick system is easy and inexpensive to set-up and maintain. Although, it tends to keep the growing medium to wet, which doesn't allow for the optimum amount of oxygen in the root system. The wick system is not the most effective way to garden hydroponically.
Nutrients

Most of the principles that apply to soil fertilizers also apply to hydroponic fertilizers, or nutrient solutions. A hydroponic nutrient solution contains all the elements that the plant normally would get from the soil. These nutrients can be purchased at a hydroponic supply store. Most are highly concentrated, using 2 to 4 teaspoons per gallon of water. They come in liquid mixes or powered mixes, usually with at least two different containers, one for grow and one for bloom. The liquids are the slightly more expensive and the easiest to use. They dissolve quickly and completely into the reservoir and often have an added pH buffer. The powered varieties are inexpensive and require a little more attention. They need to be mixed much more thoroughly and often don't dissolve completely into the reservoir. Most do not have a pH buffer.
pH

Most plants can grow hydroponically within a pH range of 5.8 to 6.8, 6.3 is considered optimal. The pH in a hydroponic system is much easier to check than the pH of soil. Many hardware, pet, and hydroponic supply stores sell pH-testing kits. They range in price from $4.00 to about $15.00, depending on the range and type of test you prefer. Testing pH is easy and essential in a hydroponics system. If the pH is too high or too low the plant will not be able to absorb certain nutrients and will show signs of deficiencies. pH should be checked once a week. It is easy to adjust by adding small amounts of soluble Potash to raise pH, or phosphoric acid to lower pH. There are also several pH meters available. These give a digital reading of the pH in the system. The pH meter cost around $100 and are not necessary in most cases.
 
Nutrient Film Technique
The Nutrient Film Technique or NFT system is an active recovery type hydroponic system. Again, using submersible pumps and reusing nutrient solutions. The NFT uses a reservoir with a submersible pump that pumps the nutrient solution into a grow-tube where the roots suspended. The grow-tube is at a slight downward angle so the nutrient solution runs over the roots and back into the reservoir. The nutrient solution flows over the roots up to 24 hours per day.

Oxygen is needed in the grow-tube so capillary matting or air stones must be used. The plants are held up by a support collar or a grow-basket and no growing medium is used. The NFT system is very effective. Although, many novice hydroponic growers find it difficult to fine tune. It can also be very unforgiving, with no growing medium to hold any moisture, any long period of interruption in the nutrient flow can cause the roots to dry out and the plants to suffer and possibly die.