Greenhouse Lettuce Production

Greenhouse lettuce has become increasingly popular among Texas growers because of the adaptable cultural requirements and profit potential.  Although several methods may be used for production, the following description outlines some of the basics.

Tube Arrangement

At present, most lettuce is grown in 2 inch PVC pipe approximately 10-12 feet long.  Plants are placed in holes drilled on six inch centers.  Many growers cover the pipe troughs with screen to catch debris and cut down sunlight which in turn reduces the growth of algae in the system.

The PVC pipe can be supported in a number of ways, but a sawhorse arrangement is most common.

To avoid many insect and disease problems, construct the frames for the tube troughs high enough to provide good air circulation.  Generally, 40-45 inches is sufficient.

Nutrient solution is pumped through the tube, bathing the roots with essential elements.  To prevent clogging, each tube trough should be fitted with an in-line filter to remove particles from the solution before recycling into the reservoir.

Crop Spacing and Scheduling

Lettuce at the 2-4 leaf stage is placed in the tubes.  As previously mentioned, plants are 6-8 inches apart and, at this stage, the tubes are arranged directly next to one another.  This growth stage lasts approximately 2 weeks.  Following this period, tubes are spaced approximately 4 inches apart to provide more growing room.  Two weeks later, the tubes are moved again to further increase the growing area.  This stage of development generally lasts another 2 weeks or until the crop is ready for harvest.

Of course, there are some variations in this production schedule and spacing but the principles generally remain similar.

Nutrient Solutions

Although several nutrient solutions may be used, the Steiners solution (with some modifications) is adequate.  Generally speaking, pH should be maintained between 5.0-6.0 and salts below 3500 ppm.  Calcium levels are frequently increased to meet plant requirements.

The nutrient solution itself should be distributed through the trough so that the entire root system is bathed.  Volume of flow is more important than speed.  Keep the slant of the troughs at a minimum.  Pumps are generally run on a 24-hour basis and the nutrient solution is recycled.

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