What is Hydroponics?
Types of Hydroponic Techniques
Deep water culture
This technique is where the roots sit directly in the nutrient solution, supported on a floating platform. The system can either be static or recirculating with oxygenated nutrient and produces high level production of leafy type vegetables and herbs.
Our 2017 trial
Installation of a deep-water culture hydroponic system within the CCF project greenhouse is currently being optimised for year-round lettuce and herb production. The system consists of large trays which can hold a depth of a few inches of solution with a layer of floating polystyrene on top. The polystyrene provides a platform for the plants to sit within small net pots with roots descending directly into the nutrient solution. The floating raft can rise and fall with water levels keeping the roots submerged.
The larger lettuces in the first picture are between 3 and 4 weeks old and were raised from seed in coir plugs before being placed within the raft system at about 2 weeks. The system had an impressive crop YIELD with a 6 week turnaround.
The experiment below shows 2 trays in production with the second just newly established as shown to the right.
Currently the rafts are separate units requiring individual maintenance, however, a connected system of trays is in development to establish a high production capacity. This involves a recirculating system where several trays will be fed from a single source. Nutrient solution will be pumped from a reservoir to the higher placed trays which will be allowed to continually drain and cascade into lower trays, eventually returning to the reservoir. This reduces system maintenance with all checks and solution replenishing done at a single point. The cascading water will have the added benefit of increasing the dissolved oxygen content of the solution.
Preliminary harvesting data of lettuce suggests yields of 8kg per m2 per annum, allowing for some reduction in growth throughout winter. This is in comparison to the current overall yield of the project at 2.2kg per m2 per annum for all types of vegetables. Within the greenhouse, the rafts should require minimal additional lighting to produce year-round, however, adaptations will be required to combat reduced temperatures. Preliminary measures of encasing the system within plastic sheeting and adding thermostats to the reservoir or individual trays may go some way to maintaining growth.
Nutrient film technique (NFT)
This technique uses a tray with a central chamber which sits at a slight incline. Plants are supported from above (typically with no medium used) with roots trailing down into a thin film of solution pumped up from a lower reservoir. The incline allows draining in a recirculating fashion and the flood is wicked with a spreader matt under the roots.
Our 2017 trials
Ebb and Flow (or Flood and Drain) also known as Dutch Bucket system is a technique where the growing area with plant roots is periodically flooded and the roots are submerged in medium, draining to a reservoir. This type of hydroponics is ideal for heavier types of fruiting plants as the system can cover a bed area or be distributed to individual plant pots.
The dutch bucket trial consists of individual plant pots connected by inlet and outlet pipes to a reservoir. Periodically the reservoir will pump the solution to the individual pots which drain through to a return pipe and should provide an ideal growing situation for tomato plants. Other simpler hydroponic experiments have been ongoing since the start of the project with a harvest of carrots grown in a bucket in a mix of perlite and vermiculite. While the carrots were perfectly straight and tasty they were quite small though they compared favourably to soil grown carrots harvested at the same time as shown in the below pictures:
On the left, soil grown carrots have been subject to pest activity, whereas, the carrots on the right have been exposed to zero pests. The bucket system consists of clay pebbles to form a reservoir in the bottom of a container with holes drilled a few inches up, a mix of perlite and vermiculite is used as a medium and root veg can be planted and fed with nutrient solution 2 -3 times a week.
Aeroponics is a technique where the roots of cuttings or young seedlings are continuously misted with nutrient in a temperature controlled tank. This technique is extremely useful for clones of valued plants and can increased rooting time by constant supply of oxygenated nutrients.
The advantages of this system are that the roots get maximum oxygenation and the system uses up to a third less water than other hydroponic techniques.
Current Trials – Indoor Farming
We have designed and built a NFT stacked vertical farm system that can accept up to 150 green leaf vegs. The system operates in a similar way to our previous NFT trials with recirculating and oxygenated nutrients pumped to the top tray and gravity fed through the stacks returning to the reservoir.