Ugrow Organic: Hydroponic Systems

There are two main types of hydroponic systems: passive and active. How nutrients are administered to the plant define these systems. Each system is well proven and each has their advantages and disadvantages.

Passive Systems

In a passive system nutrients are applied periodically in solution to the plant. Within a passive system, plants usually rely on capillarity to draw the nutrient solution from a container (e.g. saucer) up through the roots. Passive systems are not automated. As a consequence passive systems are not favoured by commercial growers because of the difficulty of watering large numbers of plants. For smaller growers, they have a lot to offer as great results can be achieved with a simple pot culture.

Pot Culture

The most popular passive system, pot culture is particularly suited to beginners as great results can be achieved for a low start up cost. Also used by more experienced growers, pot culture is a versatile method. A wide variety of plants can be grown under different environmental conditions.

Pot culture works through capillarity. A pot containing a plant is filled with a selected medium and nutrient solution is supplied via a reservoir; typically a saucer is placed beneath the pot. The medium aids in bringing up the nutrient solution by capillary action towards the plant and a stable moist environment around the root area is maintained. Although the medium will always be moist, it will also retain a lot of air spaces around the roots. The combination of constant moisture, constantly available nutrients and high levels of air supply make up a root zone for optimised for plant growth.

Pots should always be plastic and their size must be chosen in relation to what is being grown. White pots are particularly popular especially if artificial light is used, due to the extra reflectivity gained from this colour. As a guide, a recommended pot size for larger plants, such as tomatoes would be around 15 litres. A pot approximately half that size will be useful for most small plants. The other requirement is a deep saucer to act as a reservoir beneath the pot.

There are three main types of mediums that can be used in pot culture; perlite, green mix and clay pebbles. All act as an anchor for the plant and help to maintain a balance of air and moisture within the root zone.

Active Systems

An active system is automated and involves a pump being used to supply the nutrient solution to plants on a timed cycle. The solution is usually re-circulated defining the characteristic difference between the systems in terms of management. Active systems can be divided into several categories.

• Flood & Drain
• NFT (Nutrient Film Technique)
• Drip Irrigation
• Aeroponics
• Deep Water Culture

Flood & Drain (Ebb & Flow)

Compared to pot culture, Flood and Drain is a highly efficient and easy to manage system although set up costs are higher. The system consists of a table, which needs to be strong and level, and is usually plastic, with sides allowing nutrient solution to be contained inside it. Plants contained in pots with a growing medium stand on the table. Nutrient solution is pumped into the table from below to a specified level; at least half the depth of the plant pot is recommended when using clay pebbles as a medium. The solution rises up past the roots forcing out stale air residing within the medium.

The nutrient solution is then allowed to drain away via a tube connected to the bottom of the table into a reservoir below. As the nutrient solution quickly drains away oxygen rich air above the table is sucked down into the medium. Clay pebbles and rockwool mediums are used with this system; clay pebbles are the most popular. The solution level need only touch the base of the cubes if rockwool is used and plastic matting can be placed beneath the cubes to increase drainage. To prevent algae growing around the base of the pots a plastic sheet can be used to cover them and reduce the light reaching this area. The flood and drain action is repeated regularly and timers are usually connected to the pump increasing efficiency and decreasing maintenance time. An overflow pipe on the table ensures that no accidents arise if there is a problem with the pump or timers.

The frequency of Flood & Drain cycles varies between growers and mediums used. For clay pebbles at least 4 cycles per day seems to be a minimum with up to two cycles per hour if the surrounding air temperature is high. Care must be taken with the plumbing to ensure that the solution drains back into the submersible pump. The efficiency of the Flood and Drain system can be increased by raising the temperature of the nutrient solution to the range of 18 - 22 °C. This can be achieved using an inexpensive aquarium thermostat placed in the nutrient reservoir beneath the table. Oxygenation of the nutrient solution also increases efficiency and can be implemented by placing an aquarists' air stone connected an air pump within the solution. Liquid Oxygen added to the solution can increase oxygenation as well.

Nutrient Film Technique (NFT)

Of the different hydroponic methods to choose from, NFT is one of the easiest and most engaging. With NFT the plant roots grow from their propagation blocks in gullies placed in shallow streams of nutrient solution and can be seen growing and multiplying throughout the season. It is a very popular system and is now widely used widely for the cultivation of large plants such as tomatoes. For smaller plants a similar set up can be used but ensure that the size and layout of the gullies reflect the potential size of the plants being grown.

The nutrient solution should be introduced at the higher end and allowed to pass in a shallow stream down to the lower end where it is collected and returned to the tank. Also the size of the tank is important. Bigger is better as a greater volume of nutrient solution minimises the effects of conductivity and pH fluctuations which may arise.

Care must be taken with the nutrient solution to take full advantage of NFT. The nutrient solution must be properly aerated through agitation (e.g. using an air stone), and the temperature controlled with an aquarium heater (between 18-22°C).

As there is no medium to act as a buffer the nutrient solution must be of excellent quality to provide all the qualities the plant needs for growth and must contain vital chelated trace elements. On a daily basis the pH and conductivity of the nutrient solution needs to be checked (and corrected if applicable) .The pH level should be maintained at pH6. Conductivity levels may need to vary throughout the plant's lifecycle but a good starting point would be around 2 milliSiemens which is normal full strength for nutrient solution products like Optimum or Power Gro.

More information on NFT can be found on our Nutriculture advice page. Browse our NFT Systems in our online store.

Drip-Irrigation (or Micro-Irrigation)

Employed by greenhouse irrigation systems, drip-irrigation uses the principle of minimised water consumption with maximum plant growth. A submersed pump feeds nutrients solution through header tubes to secondary feed lines connected to drip emitters. A controlled amount of solution is continuously drip-fed over the medium and root system. Another tube is connected to the lower part of the garden system to recover the solution.

Aeroponics

Plant roots are suspended in highly oxygenated nutrient solution allowing easy maintenance of the roots (including inspection and pruning). A pump pushes the water with nutrient solution through sprayers, keeping the roots wet while providing a maximum amount of oxygen. Air pumps, compressors or Oz injectors provide oxygen which is crucial to healthy plant growth. The simplicity and affordability of these very active systems make them popular with home hobbyists and commercial growers alike. This technique is an excellent way to propagate cuttings.

Deep Water Culture

Deep Water Culture is a form of aeroponics. The root system of the plant is immersed in water with a bubbling aerator keeping the roots oxygenated. This technique is very good to use with plants that are heavy feeders.