Hydroponic systems are usually classified based on the method they use to distribute the nutrients to the roots. There are 3 main types:
- Nutrient film technique (NFT)
This is the simplest and cheapest in terms of initial capital outlay. Plants are propagated in growing blocks made out of materials such as rockwool, cocoa fibre or jute fibre, and are typically placed in channels that look similar to house guttering. A thin film of water circulates along the bottom of the channels and returns to a reservoir tank at the bottom of the run. The water is then pumped back to the top of the channel where it flows back again by gravity through the roots.
In an NFT system the plants’ roots are constantly in a stream of nutrient solution. The flow of nutrients is governed by the slope. Too fast a flow will damage the roots, whilst a sluggish flow will cause pooling along the joints of the channels. A 2% gradient is usually required to run a NFT system correctly.
Several channels can be connected that run from the same water reservoir. As the crop matures, the grower can adjust the nutrient levels accordingly.
Pyramid formation or a double deck is commonly used to optimise space. Some companies offer NFT systems in columns, which are referred to as “3D growing systems” because of the highly efficient use of space both horizontally and vertically.
- Flood and drain systems
Also known as “Ebb and Flow” systems, crops in a flood and drain system are typically grown in an aggregate such as clay pebbles, perlite or vermiculite. It is also possible to place plants grown in rockwool plugs into aggregate material.
However, most of the modern systems are designed to grow microgreens using the flood and drain system, typically on a growing mat made out of recycled synthetic carpets or a combination of wool and carpets. Crops can be grown in shallow trays where the water and nutrients will be delivered via a pump connected to a timer, and then allowed to drain before another circulation.
The rooting system will therefore be periodically submerged by water and then left to drain away back to the reservoir. The flooding frequency is controlled by a timer and ensures that the plant is supplied with ample amounts of water and nutrients.
Flooding and draining forces a continuous cycle of air circulation around the roots as new air replaces the pockets left by the draining water.
- Aeroponics
Aeroponics is one of the most efficient systems, but also the most challenging technically, especially for a novice grower.
No growing medium is used as the plants are grown in caged holes above a tank that houses a network of mist sprayers. The fine mist creates a very efficient environment for the suspended roots, with plenty of oxygen, water and nutrients available. Aeroponics suffered several drawbacks in its early years as engineers struggled to develop a reliable system for pumping the water at high pressure through the sprayer nozzles.
Technical requirements
The following headings summarise some of the most important aspects when managing a hydroponic vertical farming system:
- Growing mediums
These are required for ‘Nutrient Film Technique’ systems for example. Rockwool (usually marketed under the name ‘Grodan’) growing blocks work well under most conditions, from propagating seed to growing in channels. Many favour rockwool because it’s chemically inert and stable in most hydroponic solutions, and it can provide adequate water and air holding capacities.
- Nutrients
Most hydroponic suppliers will provide nutrients in powder or liquid from as part ‘A’ and ‘B’ for growth and part ‘A’ and ‘B’ for bloom. Nutrients are sold in a double combination of ‘A’ and ‘B’ because some nutrients need to be stored separate. The growth nutrients should be added to the water during the vegetative stage, and the bloom nutrients during flowering. The main difference between growth and bloom is the higher nitrogen content in growth solutions. Modern ready prepared solutions can provide all the nutrients a crop requires.
- Ventilation
Adequate ventilation is very important as day temperatures increase. Salad leaves, microgreens and some herbs in particular require excellent airflow.
- Lighting
Lighting may be required for access and safety purposes. Supplementary lighting to support growth comes as part of each micro pilot growing unit for TechTyfu.
- Meters
The pH of the water needs to be monitored every day. Different crops will have different requirements, but most will grow at their best if the pH is between pH6.0- 6.5. Likewise, the nutrient level should be monitored and adjusted accordingly on a daily basis. Charts specifying the nutrient requirements of different plants at different stages should be used when growing crops.
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