Hydroponics is a technique that allows plants to be grown without the use of soil. Soil is simply a vehicle which holds the water and nutrients a plant needs to thrive. Hydroponic systems submerge the roots of the plants directly into a water and nutrient mixture, providing all the essential elements plants need to grow. Hydroponics can be used to grow almost any type of plant, in large scale commercial crop production or small home systems. It is a popular method for growing tomatoes, lettuces and other edible plants.
There are a wide range of different hydroponics setups, but the most traditional method is known as the drip system. This method uses a pump connected to a timer to drip-feed nutrient solution onto the roots of the plants at regular intervals. When using this system, you will still need to test the solution regularly to ensure that the nutrients are at the correct level and adjust the feeding rate on the timer accordingly.
Your plants' ideal temperature will vary depending on the species. For example, tropical plants are accustomed to warmer climates, and may require heating of both the air and the nutrient solution depending on your local climate. Consult your local hydroponic specialist for the optimum temperature for your species. No matter what type of plant you are growing, good air circulation is key. Install air circulation fans to maintain a gentle, steady flow of air in the room. This has two benefits. First, it will help to increase the rate of photosynthesis, the process whereby plants convert carbon dioxide into glucose. Second, it will help boost the plant's transpiration, where water is moved through the plant into the leaf tips.
Every plant requires light to grow, however the amount of light required depends on the plant species. As a general rule, the larger or complex a plant is, the more light it will require. In a hydroponic system light is provided by lamps which are positioned above the plants, or naturally by the sun if they are being grown in a greenhouse.
Typically either fluorescent or high pressure sodium globes are used. You may need to play around with your light configuration--if the lights are spaced too far apart or too far away the plants may not receive enough light, but if they are set too close then you run the risk of burning the foliage. You should be able to comfortably hold your hand just over the top of the plant.