Hydroponic Systems Explained

There are a number of growing methods associated with the term hydroponics. Here we give a brief overview of the four main types: Flood & Drain (aka Ebb & Flow), Drip Feed (aka Top Feed), Nutrient Film Technique, Aeroponics, how they work and which particular plants grow best using each different system.

Flood & Drain / Ebb & Flow

Complete with grow tray and a solution tank connected by flexible piping, Flood and Drain, also known as Ebb & Flow, is the most common and most basic kind of hydroponic system.

The plants are placed in the grow tray which is filled with a growing media - such as clay pebbles, perlite, rockwool, coir, or some other inert substance - and the solution tank is then filled with a hydroponic mix of nutrient solution and water at the correct pH (potential Hydrogen) and strength (measured in EC values - Electrical Current) for the plants to be grown.

The Ebb & Flow system works in cycles. The solution tank is raised above the grow tray, flooding the growing media with the hydroponic nutrient solution and allowing it to soak up the solution. Once the grow media is soaked to capacity, the remaining solution is fed back into the tank ready for the next cycle - this is either achieved by lowering the tank below the tray and allowing the excess flow back into the tank under the force of gravity, or by using a pump. The pump can be used to feed the solution to the grow tray and then drain the remaining solution back into the tank. A timer can also be connected to automate this process on a regular process.

This flood and drain cycle ensures that the roots receive every major and trace element required for optimum growth as well as providing a good air-to-nutrient ratio for the roots.

The main benefits are:

• A constant supply of fresh O2 (oxygen) to the plants' roots during every cycle. As the grow tray drains the excess nutrient solution, oxygen is drawn to the roots.
• CO2 (carbon dioxide) is pushed out of the grow tray during every cycle as it is regularly flooded.
• It allows for a high density of plants.
• It is a very economical system to set up and run
• It is very simple to use and manage and is ideal for learning how hydroponic growing works and the processes involved, with immediate effect and great yields/plant growth.

The type of growing media used is up to the individual grower depending on what plants are being grown but a couple of general points to be noted are:

• Perlite drains much faster than vermiculite.
• Clay Pebbles / Grow Rocks drain faster than coir.
• Rockwool usually has a good average and is a popular compromise.

Flood & Drain systems have been used worldwide for decades, so it is a truly tried and tested system. It is particularly effective for growing herbs, tomatoes and most flowering plants.

Drip Feed Systems

A slightly more advanced hydroponic system, but also commonly used by hydroponic growers worldwide, Drip Feed Systems, also known as Top Feed Systems, consists of a Solution Tank which feeds a number of individual pots or grow bags. The plants are supported in pots or rockwool grow bags and the hydroponic nutrient solution is pumped to each pot/rockwool slab or cube, using drippers. The solution is generally fed into the top of the pot and allowed to soak down onto the roots. The tank can be connected to a timer allowing for complete control of the dripping cycle and duration of each. Once the growing media is saturated, the excess solution can either be re-circulated using a pump or be allowed to drain away - commonly known as run-to-waste.

Over the years, growers using Drip Feed Systems have determined that feeding the plants with nutrient solution at 25% in excess of the plants needs is ideal for optimum growth, maintaining the nutrient balance required for the plants. This system is generally favoured by commercial growers but is also extremely versatile and very popular with the more advanced hobby/recreational gardener.

The main benefits are:

• The individual pots can be easily removed from the system to check the plants for pests, as well as for cleaning - remember; a clean hydroponic system will produce healthier plants!
• It is easy to extend the system to include more plants, allowing for greater flexibility, particularly with larger systems.
• It requires a smaller reservoir/tank than Ebb & Flow systems, as there is less waste.
• Uses the nutrient/water solution more economically.
• There tends to be less slat build-up.
• You can use any grow media you like, depending on what works best for you - such as rockwool, coir, or pots filled with grow rock/clay pebbles, perlite, vermiculite or a mix of the two.
• The pots/rockwool cubes can be enclosed in plastic channels, keeping the roots in complete darkness and so reducing the growth of unwanted algae.

Once again, Drip Feed systems have been used worldwide for decades, so it is a truly tried and tested system and is particularly suited for tomatoes, cucumbers, peppers, herbs and flowers.

NFT - Nutrient Film Technique

Nutrient Film Technique is the truest form of hydroponics designed and perfected by Dr Allen Cooper in the 1960's and 70's. NFT is a closed, re-circulating system, which does not require a rooting medium. It is also extremely popular amongst commercial growers.

How does it work?

A very simple hydroponic system, it requires a constant supply of nutrient solution flowing over the plant's roots. This flow is a very shallow film of solution, constantly supplied by a pump and continually re-circulated from the tank and into the growing tray.

NFT systems do not utilise a growing medium (although most plants inserted into an NFT system are propagated using either perlite - easy to remove from roots - or small rockwool cubes), instead the plants are placed on a flat surface (plastic, glass or fibreglass are commonly used). These days plastic channels are the preferred method, with the nutrient film flowing through the channel.

Ideally the depth of the nutrient film should never exceed 2mm for optimum results. The idea is for the lower ends of the roots to be immersed in the constant nutrient film, which then by capillary action feeds the root mass, which develops above it. Therefore, the roots are exposed to a great mix of solution and air (02).

There are, however a number of benefits and disadvantages involved with any NFT system.

Benefits:

• No need for growing media - saving on expense
• Whole system can be fully automated - great for commercial set-ups
• No waste - as the solution is constantly re-circulated
• Individual plants can be removed from the system
• Has been tried and tested on numerous crops with excellent results e.g. lettuces, tomatoes, herbs, cabbages, cucumbers, strawberries, sweet peppers, ornamental plants and flowers and even orchids. In general, any plant can be grown successfully.
• Easy to manage and operate, especially if automated.
• Most systems are set-up on a table frame, so all work done at waist level - no bending over to tend to your plants!
• Unlimited oxygen supply for roots - as they are just suspended in the air.

Disadvantages:

• Susceptible to water-logging if film depth is too deep. Maximum of 2mm is best.
• Power faults / mal-functioning pumps will mean the roots dry up very quickly, stressing the plants and quickly leading to them wilting.
• Possibility of root infections spreading amongst plants - though not very common!
• PH /EC levels need to checked regularly

Aeroponics

Aeroponic systems are the latest innovation under the hydroponic banner and is the most high-tech of hydroponic growing systems. It is also the least forgiving of systems and requires in-deoth of knowledge of the processes and the plants requirements. Generally favoured by seasoned professionals and usually only considered for propagating plants, although complete aeroponic systems are available.

It consists of a reservoir/tank and grow trays with net pots with lids. There is no real need for growing media (except for small rockwool cubes to hold the plants in place), reducing operating costs.

How it works

The roots are suspended in an enclosed chamber and a sequence timer controls a pump, which sprays the roots with a fine mist of nutrient solution with very high levels of oxygen infused into it. The misting generally occurs every few minutes; if the roots are exposed to the air for too long they will dry out very rapidly and this is extremely detrimental to the plant.

Benefits:

• Very high levels of oxygen fed to the plant's roots.
• High levels of nutrient and water uptake by the roots.
• Very little to no waste.
• Very aggressive growth rates.

Disadvantages:

• pH / EC levels need to be constantly checked and corrected. If they are wrong the plants show adverse effects extremely quickly.
• More light is generally required than other systems for optimum growth rates.
• Generally more expensive to buy and run.

Once perfected, the growth rates tend to outweigh any of the disadvantages of aeroponic growing but it does require a lot of attention and skill to successfully use complete aeroponic grow systems.

Aeroponic propagators are the most common system used and are very successful at propagating very hard to root plants as well as for starting large crops of transplants and cuttings.

Deep Water Culture / Bubbler Systems

A variation of aeroponic systems, DWCs are extremely economical and easy to run as well as being extremely successful and very appealing to the newcomer / small-time hobby grower.

Essentially a single pot, with lid, is filled with a nutrient solution. An air stone is usually placed in the pot attached to a pump which oxygenates the solution regularly. The plant is placed in a small net pot filled with an inert media (clay pebbles or diahydro for example) which is placed in an opening in the lid of the pot.

The roots then grow through the net pot into the solution, usually only up to about an inch into it, thereby reducing the risk of the plant drowning. Fantastic growth rates can be expected.