What is hydroponics?

   Hydroponics is the science of growing plants and seeds without using soil. The name comes from the Greek words meaning 'water' and 'labour'.

   We know that all plants grow according to the conditions around them. Plants need heat, moisture, light and air in order to grow. Plants take in carbon dioxide through their leaves and give out oxygen. They need oxygen in the water around their roots. Also, plants require large amounts of seven important chemicals that are found in the soil. These chemicals are potassium, magnesium, calcium, nitrogen, phosphorus, sulphur and iron. They also need five other chemicals, but in such tiny quantities that these are known as 'trace elements'. Sometimes, one or more of these chemicals is missing from the soil. Gardeners then use fertilizers that provide the missing chemical.

   If the roots of a plant can take in enough dissolved oxygen from the water, they can grow well in water that contains the required chemicals. For instance, suppose we were to put some seeds in a small bowl with water containing all the important chemicals that a plant requires for growth. We would be doing practically the same thing as growing the plants in good fertile soil. Instead of using a bowl, we could use a tray containing material such as coarse sand, or crushed rock, or vermiculite. This material must not dissolve in water, or react with the chemicals in the water. It will provide the support needed for the plants in our tray. As the roots of the plant spread out, they anchor the plant.

   There is one other important thing that is required in hydroponics. This is air. The roots of the plants must have air as well as liquid food from the water.

   Once we have planted our seeds in the tray, we should water them with the dissolved chemicals. This should be done regularly each day. Excess water drains out into a tank beneath the tray. As it drains and passes through the tray it sucks air in after it. This can be used by the roots.

   Over a period of time the chemicals in the water solution are used up by the plants. They must be continually replaced. In commercial projects for growing plants hydroponically, the solution is pumped in from a tank. The pump is controlled automatically. The solution is tested every two to three weeks to see that it still contains the right proportions of different chemicals.

   What are the advantages of growing plants by hydroponic methods? Although it is a rather expensive method of growing plants, it is much easier to add fertilizer than when they are grown in soil. Also, they do not need watering. The main advantage is that crops can be grown in areas that are desert or have very poor soil. In hot, dry places such as the Negev Desert in Israel, and the Cape Verde Islands in the Atlantic, plants suffer severely from the weather. In these places, hydroponics has proved of great value in growing crops.

   Hydroponics succeeds best in warm areas, such as California, and especially in greenhouses where crops and flowers are grown under glass in large numbers. It was used during World War II to provide fresh fruit and vegetables for American forces stationed on some of the Pacific Islands.