Installation of a deep-water culture hydroponic system within the CCF project greenhouse is currently being optimized 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.
There are currently 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 will reduce 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, adaptions 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.
Also in development is an NFT system within a Hartley house which is being insulated and fitted with some heating and lighting installations. The large NFT trays are currently incomplete with the picture below showing the inner chamber which will sit at an incline allowing a thin layer of nutrient to flow across the plant roots.
The NFT trays will be used for a selection of compatible fruiting plants.
A type of Ebb and Flow system is also planned for development, known as a Dutch bucket system. This 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.
The results which have been achieved so far with hydroponics are promising in terms of yields and combatting pests. Future developments will provide further data and calculations should be made of external energy inputs and costs towards an assessment of feasibility as a long term growing strategy for community food production.