Gil Friend and David Morris of the Institute for Local Self-Reliance

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PLOWBOY: That makes a great deal of sense . . . but how did you go from theory to a practical application of these ideas?

FRIEND: Well the best way, always, to convince people about anything is to simply quit talking and begin doing something tangible. And that's what we did. We stopped talking and began building rooftop hydroponic gardens.

PLOWBOY: Why rooftop and why hydroponic?

FRIEND: One of a city's most underused resources—in addition to all the people who live there and all the waste they generate—is rooftops.

Here in Adams-Morgan, for example, there's a relatively small amount of available vacant land, but there's several hundred acres of rooftops that aren't used for anything. So we decided to investigate ways these rooftops could be used to grow food. Unfortunately, most of the buildings here are old and they're not terribly strong, so they probably won't support a large amount of soil . . . soil which, if it were used, would have to be brought from somewhere else. So we're building hydroponic gardens.

PLOWBOY: What do you use instead of soil?

FRIEND: We're using a lightweight mixture of two parts vermiculite to one part perlite. It weighs about 20 lbs. per cubic foot when it's wet . . . compared to approximately 80 or 85 lbs. per cubic foot for wet soil. Soil is OK if you're using a few small containers on a roof. But if you want to farm a roof instead of just puttering around up there with a hobby, then you're talking about covering most of the area . . . and that limits you to a growing medium which doesn't weigh much.

PLOWBOY: But you can't grow vegetables in just vermiculite and perlite.

FRIEND: No. In a typical hydroponics garden, the plants are actually raised on chemical nutrients which are fed to them through the rooting medium. And that's the way we did it our first year because we were more interested in demonstrating that gardens could be grown on rooftops than we were in experimenting with new techniques.

Obviously, however, this chemical approach leaves a lot to be desired. To begin with, the mixtures we feed the plants contain only the substances we know a plant needs. But maybe we're not as smart as we think we are. Maybe plants need some nutrients we haven't learned about yet.

MORRIS: There are other problems, too. Chemicals are imported from outside the neighborhood, their manufacture requires large amounts of fossil fuel energy, and—finally—they ignore resources we have here . . . namely the organic wastes which we generate. So this year we're trying to garden hydroponically with organic nutrients produced right here in the community.

F RIEND: Yes. We started by mixing one part compost into two parts of the vermiculite-perlite mixture. So we're essentially still working with a lightweight soil. Our next experiment will be to use a sort of tea-which we'll make from compost—as an organic nutrient. Then we'll compare the growth and quality of the plants raised on the tea with those produced by the other systems we've tried.

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