Three non-circulating hydroponic methods for growing lettuce are described
which do not require electricity, pumps or wicks. All of the nutrient solution is
added prior to planting or transplanting. In the simplest system, lettuce is seeded in
a tapered plastic net pot filled with growing medium and placed in a darkened, 4-
liter plastic bottle filled with nutrient solution with the lower 3-cm-portion of the
pot immersed in nutrient solution. Plants are automatically watered, because the
entire growing medium in the net pot becomes moistened by capillary action. Plant
growth reduces the nutrient solution level, creating an enlarging moist air space.
Meanwhile, the root system expands and continues to absorb water and nutrients.
Leaf and semi-head lettuce cultivars are usually harvested at about 6 to 7 weeks
after seeding. A typical expansion of this concept to a commercial scale employs a
14 cm high tank lined with polyethylene sheeting which is filled with nutrient
solution and covered with an expanded or extruded polystyrene sheet resting on the
tank frame. Lettuce is planted or transplanted into net pots filled with growing
medium and placed in holes in the cover. Lettuce seedlings are initially watered by
capillary action, and later, by direct root uptake. The crop is harvested before the
nutrient solution becomes exhausted. Another modification of this method is a
float-support system in long rectangular raceway tanks. Lettuce is planted or
transplanted into net pots placed in a sheet of extruded polystyrene. The cover
initially floats on the nutrient solution, and then, comes to rest on 2 parallel plastic
pipes (10 cm diam) resting on the tank floor as the nutrient solution level recedes
due to plant growth. The tank is filled with water immediately prior to harvesting
and floating rafts may be easily moved to a harvesting station.