Plant Growth Factors
Hydroponic growing allows the indoor gardener to completely control the growing environment. All of the elements your plants need to grow must be provided by your indoor hydroponic system. Lighting, temperature, oxygen, CO2, pH, and nutrients should be considered before starting the set up of your growing system.
Light and Photosynthesis
Plants convert carbon dioxide and water to create essential sugars through the process of photosynthesis. Light is crucial because it provides the energy needed for this conversion. The intensity of the light has been shown to increase the amount of sugar produced. This will keep going up until the plant reaches its saturation point for light, so you should always try to increase the amount of light your plants receive. Plants grown in an outdoor garden would normally receive 8-12 hours of sunlight per day, depending on the season. You should try to simulate this as well as possible to maximize photosynthesis. Make sure to space plants out enough to avoid having them block the light from each other.
Inadequate lighting will cripple your plants and may leave lasting developmental damage even after lighting conditions are improved. The stems will be spindly and elongated, causing them to have difficulty supporting your plants as they grow. Fewer leaves may develop and the leaves that do grow will not expand to their normal size. As the plants mature, they will not be able to flower or bear fruit and may even turn yellow depending on the length of the lighting deficiency.
Low carbon dioxide (CO2) levels can also limit your plant's ability to photosynthesize. Plants can process much more CO2 than is normally found in the atmosphere. You can increase the amount of CO2 available to your plants by including a CO2 system in your indoor hydroponic setup.
Good ventilation will keep your plants cool and circulate the air so a fresh supply of CO2 and oxygen are available at all times. An oscillating fan set on the same timer as your lights should provide enough airflow for most indoor gardens, but larger setups will obviously need a more complex fan setup.
Depending on the type of indoor hydroponic system you use, water quantity may or may not be a problem. Whichever system you choose, make sure to always keep adequate water for your plants. Water deficiency causes permanent loss of production, even if it is corrected quickly.
Water quality, on the other hand, can be a serious problem for any hydroponic growing system. Tap water in many places contains minerals and salts, which can alter the nutrient balance of your hydroponic solution. This is usually called "hard water" and can often be offset by adjusting the mix of your nutrient solution. Try to keep the salt content of your water below 325 parts per million (ppm) whenever possible.
Plants grow best within a certain range of temperatures. Extreme temperatures may lead to stunted growth and lack of fruit production. Of course, ideal growing temperatures can vary from species to species, but warm-season vegetables and many types of flowers grow best between approximately 65° and 80° F. Other cooler-season vegetables like lettuce usually grow best between 50° and 65° F.