While there are many different Hydroponic systems available to the indoor gardener, they can almost be broken down into three common approaches.
A) Recycling Systems
B) Run to waste
C) Passive or static set ups
These can be classified as being based on a solution culture or around a medium culture.
The solution type has four sub categories,
* Continuous Flow namely NFT (Nutrient Film Technique)
* Aeroponics
* Flood and Drain also known as Ebb and Flow
* Top Irrigation
Continuous flow systems have been around for many years and have been tried and tested by some of the valued members of the community, and on overall balance, the NFT, [nutrient film technique] system is generally regarded as probably one of the more productive techniques.
All systems have their own strengths and weakness, so it is good practice to learn about them, and then you may examine these pluses and minuses in relation to all the factors required to yield a successful harvest.
NFT (Nutrient Film Technique)
A steady flow of nutrients is pumped to the top of a growing table, which is designed to have a slight fall, or pitch on it. This allows the water and nutrients to flow down the table and across the roots providing a nutrient film, hence the name. This mixture of water and nutrients goes back into the tank and is continuously pumped around the system whilst the lights are on and the pump is turned off when the grow lights are turned off.
The solution is changed from time to time, to meet the plants needs, as they use up the nutrients and to avoid a salt build up. Changing of mixture is approximately ever ten to fourteen days, however some nutrient manufacturers will provide their own schedules. Basically for the different stages of the plants life cycle, such as the growth stage and that of the flowering stage, often a booster is added part way through flowering period to increase yield.
The table has channels for the solution to travel down. This provides the means for a steady flow of nutrients, very similar to looking at the cement in between the bricks of a brick wall. The table is also a spreader mat placed on it to encourage even distribution and a cover plate is fitted and holes cut where the plants are positioned. Planting in a herring bow effect, rather than in line is the most popular and is believed to achieve better results. Most growers will put their cuttings or seedlings in rock wool cubes, but we will compare growing mediums later.
The NFT system is a very flexible system as you can decide on the number of plants per table, the design suites a practice called sea of green and is often used to grow salad crops where a large number of small plants are grown in a compact manner for high yield effect, as more light reaches the target, bigger plants will inevitably block light from younger stems and shouts, for example of effective use of lights and how fast artificial light fades from light source output.
Larger plants do not always sit comfortably in this type of system, but this can be over come by supporting the plants with strings or sticks, and also using larger blocks.
Most of the time there is no problem as the roots inter twine to form a dense like mat.
Aeroponics
They say that sometimes a picture can say a thousand words.
In this case the picture below shows aeroponic propagation. The cutting or plant is generally placed in a rock wool cube as in this case or supported with clay pebbles. The roots are allowed to dangle in a darkened chamber and sprayed with a fine mist like solution through small adjustable spray heads.
The water and nutrients should be heated about 5 degrees lower than the top of the plant to avoid stress and aid nutrient uptake, it is also advisable to use this principle with NFT, common sense must prevail and this should be applied if the grower is experiencing abnormal high temperatures. As a general rule the warmer the water the less oxygen it will have. Some growers use an air stone or pipe similar to that used in a tropical fish tank to boost the oxygenation level. Overall this system is mainly used for propagation purposes. The plants tend to be cut out or gently removed from the cup and delicately inserted into rock wool.
Flood and Drain also known as Ebb and Flow
There a number of variations of this, but the most common one is that plastic buckets or pods are placed on top of a reservoir and the buckets are filled with a growing medium. The most common medium is clay pebbles.
At regular intervals a simple timer causes a pump to fill the pods, after which the solutions drains back down into the reservoir. This keeps the medium regularly flushed with nutrients and air.
In practice this type of system can have certain draw backs. The first one is the use of clay pebbles. As the nutrients are pumped up into the pods the clay pebbles move, firstly up with solution and then down, this process happens many times in the plants life cycle. As the pebbles move an abrasive process takes place in a way like watching pebbles on the beach being moved by the tide, which means that small grit like pieces go back into the reservoir and have potential to size the pump. A way round this to religiously sponge out the bottom of the reservoir and to clean the inside of the pump, it is time consuming but strongly recommended.
The clay pebbles can break up in such a way that they block the nutrient supply tube when the solution is allowed to drain back. This leads to some of the pods not getting enough nutrients or oxygen, the plants will still live but results will be more modest. It is difficult and messy to try and fix this problem. With older systems leaks can occur where the tube is drilled into the side of the pod so it is wise to make sure all your electrics are safe and to keep a sponge, bucket and towel handy. It's not nice to think while your away water could be seeping through the floor.
The clay pebbles will accumulate a salt build up, which will need to be sorted out when they are reused. NFT does not have this problem as the spreader mat and rock wool cubes are rolled up and disposed of, but the clay pebbles have to be separated from the mass of roots and this takes a lot of water and time. The clay pebbles then have to be boiled to remove the salt build up and then soaked in a neutral PH solution before they can be used again. If you had eight pods all capable of holding twenty litres, that is 8 times 20 = 160 litres and a large saucepan might hold 3 litres to the top, means that you will have to boil the saucepan at least 64 times!
Top Irrigation
Feeding your crop from the top, similar to watering from a watering can
The nutrient solution is distributed by a selection of adjustable nozzles usually at the base of each plant. A timer is used to determine the watering cycle and the nutrient is allowed to return to the reservoir for the next watering cycle.
Run to waste
This is the term used for hydroponic systems that do not recycle the nutrients. The plants are given smaller amounts of food, and at such a rate that a small amount of the solution is regarded as a by-product from the subject. This excess is often captured in a tank or bucket and disposed of, salt build up could be an issue in one of the recycling systems, but is not often referred to in this type.
The amount of excess nutrients can sometimes be considered a matter of trial and error, some growers aim for an overflow of about ten percent, but it seems a fairly labour intensive system and all excess nutrient solution should be disposed of in an environmentally way as possible, and not just down the sink, as with similar systems. There are still a few active ingredients, when using some nutrients. Relative on their price and related factors, this system might prove to be more costly to operate. A run to waste system, might fall into this category.
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