THE NUTRIENT FLOW TECHNIQUE

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In addition, a third tank-which holds water to replace liquid losses caused by transpiration and evaporation-can be added to automate even more of the process. The replacement liquid is introduced into the lower tank when a float valve trips. And that's all there is to it! Basically, the Nutrient Flow Technique system is a closed loop that uses gravity to supply the fertilizer to the growing bed and a pump to raise the liquid back to its starting point.

LATTICE YOUR LETTUCE

The NFT approach allows a great deal of flexibility in the layout of the growing beds. Tomatoes and cucumbers started in Kys Kubes or Jiffy-7's (available in most garden supply stores) can, for instance, be grown in sections of plastic roof gutter without any growing medium. Or, if you fill the gutters with several inches of perlite, you can raise cauliflower or other heavy-heading produce. A lattice grid of 2 X 4's-with a sheet of plastic forming channels between the boards-will support a huge crop of butterhead lettuce in a sparse two inches of perlite, while a slightly sloping bed of plywood-with 1" X 6" sides and a polyethylene liner-can be constructed to almost any dimension and used for just about any vegetable from radishes to beets.

VERTICAL VEGETABLES

Tall plants, such as tomatoes or cucumbers, are common in hydroponic culture, but NFT allows normally "horizontal" crops-such as lettuce, spinach, or even houseplants-to be grown in spacesaving, sun-seeking vertical gardens. Two-inch-diameter PVC pipes-pierced with holes that accommodate preplanted Jiffy-7's-become lush green columns (the nutrient gravity-feeds in at the top . . . moistens the roots as t flows down inside the pipe . . . and is collected at the bottom to be cycled back again). A similar space saver is the "cascade" arrangement, in which slightly sloping (alternately right and left) PVC-pipe beds are positioned one above another. The nutrient solution flows in at the high end of the top pipe, passes from the low end of that tube to the high end of the next one, and zig-zags its way to the bottom . . . feeding the roots all the way down.

It's even possible to make a "radish Aframe" from plywood sheets covered first with plastic and then with capillary matting (sold by greenhouse specialty stores). Simply sew felt weatherstripping onto the matting, and tuck your radish seeds into the flaps. A plastic feed pipe-on top of the structure-delivers a constant stream of nutrient solution, which flows down the matting to catchment gutters at the bottom . . . and then, of course, the liquid is pumped back up to the top.

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