Carbon dioxide - CO2 - is an essential ingredient of cannabis (or any other sort of plant, for that matter) cultivation.
Though considered by people as a bad thing - emission of carbon dioxide is partlyresponsible for global warming - for plants it serves as feed.
In short, without enough CO2 you won't get marijuana.
The natural concentration of CO2 in the air is approximately 340 ppm - parts per million.
Most plants, however - including cannabis - are able to process more of it, up to 1000 ppm.
With more CO2 in the air, your plants will grow stronger and faster.
It is said that increasing CO2 level to 500 ppm can lead to 15-25% faster growth, 40% if 700 ppm is achieved and up to 50% with 1000 ppm.
Above that level it is no longer increasing the speed of plant's development.
As the plant consumes the CO2 from the air, if it is kept in small area for long time without proper ventilation, the concentration of carbon dioxide could fall, leading to slower growth.
When CO2 level falls to 150 ppm, one could observe up to 40% slower growth.
That is why supplementing your plants with CO2 is very important.
Ranging from CO2 tabs that you dissolve in water, through easy to use CO2 pumps to professional dispensers, there are fortunately multiple ways that this crucial compound could be delivered to your plants.