Assembly line hydrophonics

Hydro Harvest production greenhouse---stuns the visitor with its nearly wall-to-wall contents of green. It's a rabbit's dreamland: three 9-foot-wide mats of densely planted lettuce, elevated waist-high and slightly aslant, running the length of the greenhouse with only narrow aisles between. Everything looks ready to eat, but closer inspection reveals that each house-long strip of plants starts with seedlings at the far end and offers mature heads only nearest the greenhouse entrance. The seemingly unbroken ribbons of planting actually consist of hundreds of nine-foot sections of white plastic rain gutter laid side by side like ties on a railroad, each filled with perlite and sporting eleven lettuce plants spaced along its length.

A section of seedlings, placed on the rails with gutters edge to edge, begins the process at the back end of the greenhouse. After one to two weeks of growth, depending on the season, the whole section is rolled forward. As the gutters are moved ahead, they are also spread apart on the skids, to make room for more growth. Then a new section of seedlings is added behind the section that has advanced. More moves follow after additional growth, until there are four sections on the tracks, and the initial planting has reached the other end of the house---by which time its gutters have been spaced several inches apart to correspond with the breadth of full-grown plants. After harvest, the liberated gutters in the lead section are topped off with new perlite and shifted to the rear to take on more seedlings, while the three remaining sections move ahead again.

The system makes optimum use of available space and ensures that plants are ready for harvesting when they arrive at the end of the greenhouse from which they will be shipped. The system also works well for feeding. The support rails under the gutters are designed so that the gutters slope for drainage. Long, black, four-inch vinyl pipes, suspended over the high edge of the gutters, act as reservoirs for the nutrient fluid. Hundreds of tubes project from the larger pipes, and the nutrient solution drips into the perlite and heads downslope. What the plants don't drink and the perlite doesn't absorb runs out the lower ends of the gutters into drain channels, which carry this unused solution to sumps, where pumps return it to the overhead pipes.

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