As explained in our Plant Growth section, carbon dioxide (CO2) is required by plants during the photosynthesis process. During photosynthesis, CO2 is combined with water, nutrients, and energy from the sun (or grow light) to produce essential sugars that provide the plant's energy. Lack of any key element needed for photosynthesis will limit the plant's growth to the point of that deficiency. Always keep in mind: A chain is only as strong as its weakest link. If any one element is missing, the entire growth process will be affected.
Using a CO2 injector is the least expensive way to add CO2 to your indoor garden's environment. These usually consist of a valve, regulator, and a gauge to measure the amount of CO2 being injected into the air. Some of the more sophisticated CO2 injectors also include a timer to control the timing of the CO2 release. CO2 tanks are generally sold separately and can be found at home health or restaurant supply stores.
If you plan to use your indoor hydroponic system for a long time or for several crops, it may be wiser to invest in a CO2 generator. CO2 generators produce carbon dioxide through the burning of propane, natural gas, or any other carbonaceous fuel. They are significantly more expensive than a simple injection system, but you will eliminate the cost and hassle of buying CO2 tanks. Over a long enough period of time, the CO2 generator ends up cheaper than an injector and many tanks.
CO2 Monitors and Controllers
For large-scale gardeners (or those with extra cash to play around with), a CO2 monitor with controller can automatically maintain your indoor garden's CO2 levels at a selected level. These systems can be very expensive, costing hundreds of dollars, but are a nice addition if you can afford it. There is usually an electronic CO2 monitor connected to a controller, that is then connected to a CO2 generator to ensure that the garden always stays at the user's preset CO2 level. Some monitors are sold separately and are compatible with many types of controllers, allowing greater flexibility when designing your garden.