Hydroponic gardening refers to ways of growing plants without using soil. It encompasses several different ways of growing a garden. It is often done indoors using either natural or artificial light, but it can also be done outdoors. Rather than using soil as the method of delivering nutrients to the plant, hydroponic gardening uses other techniques. If the plants receive their nutrition in other ways, get adequate sunlight, and are anchored firmly enough for them to remain upright, soil is not necessary for them to grow. What they do need is a growing medium, adequate light and nutrition.
One of the things soil provides in traditional gardening is support for the plant's roots. It gives the roots something to grow in and anchor the plant in an upright position. Hydroponics often uses a growing medium for this purpose. This can be a rock wool, which is made from volcanic rock and looks a bit like fiberglass insulation. It is a versatile material for growing plants, and it is low in cost. Expanded clay can also be used. It retains moisture well and looks like small marbles. Another growing medium, called "coco," is made from coconuts. Other methods include expanded mineral compounds such as perlite, which are also widely used in potted plants with soil. The plants in a hydroponic garden are planted into this substance, rather than soil. It gives them a place for their roots to hold onto, and it can help to retain moisture and provide a method of delivering nutrients to the plant.
In traditional gardening, soil also provides a way for nutrients to reach the roots of the plants. In hydroponics, the soil is not necessary because the nutrients are provided in other ways. Purchased nutrient materials are usually delivered by spraying the roots, such as in aeroponics, where the roots are mostly suspended in the air, or by putting them in a soaking solution so the nutrients can be absorbed by the plant's roots through the growing medium. Different plants and conditions require different types and amounts of nutrients. For instance, for tomatoes, use 1.5 oz. Mittleider Pre-Plant Mix. For lettuce, use 2 tsp. hydroponic fertilizer, 1 tsp. Epsom salt and 2 tsp. calcium nitrate.
Some systems use a pump, much like an aquarium pump, which is immersed in a nutrient solution. The roots are suspended in this solution, and the pump oxygenates it. Another method of delivering the nutrient solution is through a drip system. A pump will pump the solution gradually over the roots, so that it can be absorbed. "Ebb and flow" systems have scheduled times to release the nutrient solutions, and they also have dry periods where they are not pumping out the solution. The dry periods allow plants to absorb oxygen from the air. Still another method is for the gardener to simply spray the solution on or near the roots.
Many companies now offer kits which have everything you need to start your own hydroponic garden. Look around for different types of mediums, and see what would be best for the plants you intend to grow in it.