Introduction

IN RECENT YEARS GROWING PLANTS HYDROPONICALLY--that is, with the roots in a medium other than soil--has stirred the imagination of many persons interested in plant growth and development. Commercial growers have adopted hydroponic methods to produce crops in circumstances that would otherwise be unfavorable. For the plant hobbyist, hydroponics offers an opportunity to learn more about the growth of plants and their interactions with their environment. Gardeners may grow flowers, ornamental plants, and vegetables by hydroponics. Growing your own fresh vegetables out of season can be a special winter treat.

Colorful sales campaigns and articles in the popular press have led people to believe that hydroponics is a new discovery that will revolutionize modern agriculture. However, the basic techniques have been used by plant researchers for well over a century to determine the effect of particular nutrients on plant growth and yield. The first recorded experiments were conducted in England in 1699 by Woodward. By the mid-nineteenth century, Sachs and Knop, pioneers in this field, had perfected a method of growing plants without soil. In the late 1920s and early 1930s Gericke was able to grow plants successfully on a large scale by adapting the laboratory technique of solution culture.

The widespread use of hydroponics for commercial plant production is a relatively recent occurrence. In areas where soil is lacking or unsuitable for growth, hydroponics offers an alternative production system. However, there is nothing magical about hydroponics. Equally good crops can be produced in a greenhouse in conventional soil or bench systems, often at lower cost.

The term hydroponics is used to describe many different types of systems for growing plants without soil. Among the most common are:

• water culture, aquaculture, or nutriculture, a system in which the plant roots are immersed in water containing dissolved nutrients
• aggregate culture, in which a material such as sand, gravel, or marbles supports the plant roots
• aeroponics, in which the plant roots hang in the air and are misted regularly with a nutrient solution
• continuous flow systems, in which the nutrient solution flows constantly over the plant roots. This system is the one most commonly used for commercial production.

Often grouped with these systems is drip or trickle irrigation but it is not a true hydroponic system.

The common denominator in all hydroponic systems is the method by which the plants receive their nutrition and water. When plants are grown hydroponically their roots are either immersed in or coated by a carefully controlled nutrient solution. The nutrients and water are supplied by the solution alone, not by the aggregates (if any) that support the roots.
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A number of packaged hydroponic systems are available to the commercial grower and hobbyist. Individuals, who lack building skills or plant-growing experience can look to these kits as an introduction to a challenging hobby. Similar systems can be built at lower cost, however, by talented hobbyists. Only experienced greenhouse operators should consider hydroponics as a commercial venture.

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