Hydroponics Lettuce Production
Hydroponic Lettuce and Watercress Production
Lettuce and Watercress are both grown in a very similar system; the preferred system is NFT
(Nutrient Film Technique). The NFT system uses sliding gullies inside a structure.
Gullies are made using the 100 x 50mm rectangular hydroponic channel with a flat base, do
not use round pipes, as the true film of nutrient cannot be achieved.
Sliding gully systems are usually inside a structure, and have gullies custom manufactured to fit
the structure size. More plants per square metre can be fitted into this area compared to the
old fixed bench system.
Seeds are germinated in a sterile media such as Vacroc Rockwool blocks, or in grow pots,
again in a sterile media such as Perlite, Vermiculite, Sterile Pumice or mixtures of these. Flood
and drain trays are usually used for propagation, with horticultural lighting for consistent
production year round.
The seedlings from propagation are placed into the gullies at one end of the system, and
progress down the system, moved manually each time plants are harvested, until they reach
full size.
Feed and return pipes are sized according to the number of benches and flow rate required.
Tank and pump size are also determined by the number of gullies and head required to reach
the highest point.
NFT systems require nutrient to circulate 24 hours per day.
Propagation to End Product
Seed germination is done in two stages. The first stage is in Flood and Drain tables preferably
under grow lights. You would leave the plants here for up to a week with just water in the tank.
Then the young seedlings would be moved out to another flood and drain table at the end of
the greenhouse. They would be left here for a further one to two weeks nutrient to feed them.
Once they have been transferred to the sliding gullies, they will be fed nutrient at the optimum
strength and pH. The strength and formula will vary according to crop type, local temperatures
and time of year.
The time from germination to maturity varies with temperature, time of year and crop type, but
ranges from 21 to 50 days.
Nutrients
There are several types of nutrients mixes designed for Iceberg lettuce, Fancy lettuce and
watercress, with summer and winter formulations available where necessary.
Nutrient Formula mixes can be blended to suit your water supply and crop type and are given
a special mix code. A copy of your water analysis or a sample of water for analysis is necessary
for these customized mixes, with no extra charge for this service.
Medias and Equipment
Suitable media for pots and plug production include:
Sterile pumice, 1 to 5mm in size, 60% Perlite mixed with 40% Vermiculite or coarse washed river
sand.
Suitable pre-made Vacroc Rockwool Blocks are ideal for lettuce and watercress, the size to use
for these crops is the 25 x 25 x 40mm cube with straight sides (no taper).
Grow pots are available in either reusable (white) or disposable (green). Flat bottom trays with
no holes in the base are available for reusable pots and Vacroc cubes. The disposable pots
have a special carry tray to suit the flexible material.
Test and Control Equipment
It is advisable to have a fully automatic nutrient dosing system; it is also a good idea to have a
heat pump. This will heat the nutrient in winter and cool it in summer for optimum growing
conditions. Good airflow is essential for healthy plants, and temperatures over 30 degrees C
must be avoided where possible.
Seed Varieties
There are literally hundreds of different types of plant varieties available, and it is essential to
carry out trials of the many types to determine the varieties that suit your climate and market.