Gardeners with little space take a shine to 'soilless gardening'

Jim Taylor doesn't believe a nationwide food crunch is inevitable in this country. In the future, he believes, a very significant food supply will come directly from American backyards. Many among the nation's 34 million food gardeners are already showing the way, and more will follow their lead as commercially produced food becomes less abundant and more expensive.

These backyard truck farmers will grow large volumes of food in relatively restricted areas, employing intensive growing techniques, including hydroponics.

Hydroponics (literally working water) is the technique of growing plants without soil. Other terms for the practice are ''soilless gardening'' or ''sand culture.'' The most common approach, particularly among home gardeners, is to grow plants in an inert medium - gravel, perlite, sand, and the like - which is then regularly irrigated with a complete nutrient solution - one that contains every element needed for plant growth.

High yields from small areas are possible by this method because it relieves plants of the need to compete with one another for nutrients and moisture. The food is brought to the roots - a form of room service, you might say - every time the solution is pumped into, or poured over, the growing medium.

For many years hydroponics was regarded as a totally chemical approach to gardening. But over the years some growers have seen the advantages of including some natural organic approaches in the system. James Taylor is one of them, and his recently published book, ''Grow More Nutritious Vegetables Without Soil,'' (Parkside Press) describes his approach as the ''new organic method of hydroponics.''

Organic purists might dispute the claim, because Taylor recommends using a conventional hydroponic fertilizer (all chemical) as a base in the plant-feeding program. But thereafter he adds seawater, sea solids, or seaweed extracts to enrich the solution still further.

By meeting more than just the basic nutrient needs of vegetables (as with hydroponic fertilizer alone), you get more nutritious and better-flavored vegetables, Taylor contends.

The sea, he says, is a rich ''biotic soup which contains all the necessary ingredients to support the abundant life in it.'' Hydroponic vegetables, in fact , have been grown successfully in a nutrient solution made up only of sea water and fresh water in a ratio of 1-4. ''Highly nutritious crops,'' in Taylor's words, were the result of that seawater experiment.

Taylor's organic approach, which does not stop with seawater, also includes beneficial bacteria, available from some hydroponic suppliers or from garden centers in the form of biological compost starters.

These beneficial bacteria apparently provide the same form of biological control in the hydroponic gravel as they do in garden soil. They check the development of pathogens (harmful microorganisms); help keep the pH in balance; and, by feeding on the dead root tissue, reprocess it back into nutrients for the plants.

Taylor suggests introducing bacteria (generally available in powder form) every two months.

Hydroponic systems for the home gardener have been on the market for several years. Many come with pumps and timers so that the growing medium is automatically flooded three times a day, whether you are at home or away on vacation. This way your gardening activities are largely limited to planting; a little pruning, perhaps; and harvesting.

As Taylor puts it: ''With hydroponics you can eat well from your garden and still have time for golf.''

If you want to try hydroponic gardening yourself, you might start out with inexpensive, homemade equipment. Take a wooden box 12 or more inches deep and line it with plastic. Drill a drainage hole at one end and slope the box in that direction. Fill the box with gravel or coarse sand and water with a nutrient solution at least twice a day. Place a plastic bucket under the drainage hole so that you can collect the nutrient solution for repeated use.

When I experimented along these lines many years ago, I would water the plants before I left for work in the morning and again immediately after I returned home in the late afternoon.

By most hydroponic standards, this approach would be deemed haphazard at best , but it worked for me. Tomatoes, in particular, did well - and so did a bed of strawberries where sawdust was used as the growing medium.

Several books have been published on hydroponics for the home gardener, including Taylor's, which I find to be thorough and sound throughout. The Parkside Press address is PO Box 11585, Santa Ana, Calif. 92711.