We are so used to plants growing in fields and gardens that we think anything else is completely absurd. But in fact: not only do plants grow without soil, they often grow much better when their roots are in water or very humid air instead. Growing plants without soil is called hydroponics. It may sound strange, but many of the foods we eat - especially vine tomatoes - are already grown hydroponically. Now here's a brief explanation of exactly how hydroponics works....

Plants grow through a process called photosynthesis, where they use sunlight and a chemical called chlorophyll in their leaves to convert carbon dioxide (a gas from the air) and water into glucose (a type of sugar) and oxygen. If you write this down chemically, you get this equation greatly simplified:

6 CO2 + 6 H2O → C6H12O6 + 6 O2 Carbon dioxide + water = sugar + oxygen   It turns out that the soil in which plants commonly grow does not appear in this formula at all. What plants need is only water, air and nutrients, both of which can be obtained from the soil. But if they can get these things elsewhere - for example, by standing with their roots in a nutrient-rich solution - they can do without soil at all. That is the basic principle of hydroponics.

In theory, the word "hydroponics" means growing plants in water (from two Greek words meaning "water" and "work").

Although the benefits of hydroponics are sometimes questioned, growing without soil seems to have many advantages. Some hydroponic growers have found that their yields are many times higher when they switch from conventional methods to hydroponics. Because plants grown hydroponically have their roots immersed directly in nutrient-rich solutions, they get the nutrients they need much more easily than plants grown in soil. With smaller roots, you can grow more plants in the same space and get more yield from the same area (which is especially good if you're growing in a confined space like a greenhouse or on a balcony or windowsill indoors). Hydroponic plants also grow faster. Many pests are transmitted through soil, so not using soil generally makes for a more hygienic growing system with fewer disease problems. As hydroponics is ideal for indoor growing, you can use it to grow plants all year round. Automated systems controlled by timers and computers largely automate the process.

There are also disadvantages: One is the cost of all the equipment you need - containers, pumps, lighting, nutrients and so on. Another disadvantage is the ponic part of hydroponics: it involves a certain amount of work. With conventional growing, you can sometimes be quite careless with the plants, and if the weather and other conditions cooperate, the plants will still thrive. Hydroponics, however, is more scientific and the plants are much more under your control. You have to constantly monitor them to make sure they are growing in exactly the conditions they need (although automated systems, such as timers for lighting, make things a lot easier). Another difference (which is arguably less of a disadvantage) is that hydroponic plants have a much smaller root system and so are not always good at supporting themselves. Highly fruiting plants may need quite elaborate support devices.

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