Let us first look at some basics. Photosynthesis is the process by which plant leaves make carbohydrates. Specifically, sunlight, CO2 and water are converted into carbohydrates and oxygen (O2) by the action of chlorophyll in the plant’s chloroplasts.
When plants are able to maximize the process of photosynthesis, the result is larger plants with larger yields. However, plants growing indoors under artificial light often lack enough CO2 to efficiently photosynthesize. Plants can quickly use up the available CO2 and convert it to O2. When O2 levels rise too high, stomata on the leaf surface close and plant growth virtually stops.
Growing areas that have limited or no air-circulation can be affected even more. Lack of air movement causes CO2 that would be used by plants to become unavailable due to its distance from the leaf (usually down low in the growing area). Moving air helps solve this problem.
Adequate levels of light, water and nutrients are needed for good plant growth. Therefore, it might seem logical to assume that the growth-promoting effects of indoor CO2 enrichment would be reduced when these essential resources are present in less-than-adequate amounts.
In many instances, however, the percentage of growth enhancement provided by indoor CO2 enrichment is even greater when these important natural resources are present in sub-optimal quantities. When they are in such short supply that plants cannot survive under ambient CO2 concentrations, elevated levels of CO2 often enable such vegetation to grow and successfully reproduce where they would otherwise die.
One of the reasons that plants are able to respond to indoor CO2 enrichment in the face of significant shortages of light, water and nutrients is that CO2-enriched plants generally have more extensive and active root systems, which allows them to more thoroughly explore larger volumes of soil in search of the things they need.
Ambient CO2 levels (percentage of CO2 in the air with any enrichment) typically hover around 400 parts per million (ppm). Indoor plants can quickly convert this CO2 through photosynthesis and deplete available CO2. When CO2 levels fall to around 150 ppm, the rate of plant growth quickly declines.
Enriching the air in the indoor growing area to around 1,200 to 1,500 ppm can have a dramatic effect on plant growth. Growth rates typically increase by up to 30%. Stems and branches grow faster, and the cells of those areas are more densely packed. Stems can carry more weight without bending or braking. CO2-enriched plants also have more flowering sites due to the increased branching effect.
CO2 enrichment also affects the way a plant can tolerate high temperatures. At the highest air temperatures encountered by plants, CO2 enrichment can often mean the difference between living and dying.
It typically enables plants to maintain positive carbon exchange rates in situations where plants growing under ambient CO2 levels would normally exhibit negative rates that ultimately lead to their demise. This is because CO2 enrichment affects transpiration by causing the stomata to partially close, which slows down the loss of water vapor into the air. As such, foliage on CO2-enriched plants is much thicker and slower to wilt than plants grown without CO2.
There are many alternatives to traditional CO2 production. The composting of organic matter results CO2, so many large-scale greenhouses have composting rooms adjacent to the growing greenhouse (the CO2 is pumped from one room into the other with circulation fans). One drawback, however, is that composting so close to your growing area can attract potential crop-damaging insects.
The process from beer making—that is, using sugar, water and yeast—has also been used. Not a bad deal if you like to brew beer. The yeast eats the sugar and releases alcohol and CO2 as by-products. If you are not into brewing beer, you can simply mix brewer’s yeast and sugar with water.
Keep in mind, though, it is important to have the temperature of the water right—water that is too hot will kill the yeast and water that is too cold will not activate the yeast. The process is simple and inexpensive, but it does have some drawbacks. Mainly, it can present an odor problem and it is somewhat time-consuming as you have to remix the brew every four to five days.
Dry ice, which is frozen CO2, releases gaseous CO2 when exposed to the atmosphere. Dry ice has no liquid stage, which makes it easy to work with and has little clean-up. However, dry ice can be expensive for long-term use and it is difficult to store. Using insulated containers can slow the melting process, but it cannot be stopped.
Mycelial-based CO2 production is relatively new way to introduce CO2. Mushrooms are more like humans in that they exhale CO2, and a non-fruiting strain of mycelium has been discovered that continues to produce CO2 for at least half a year (above-ambient CO2 levels can still be detected up to 16 months later). There is no maintenance or set-up with this option, and the low cost makes mycelial-based CO2 a good option.
As a grower, you know the time and energy you spend working your indoor garden is tremendous. Adding CO2 is not only a good idea, but is necessary to have the most efficient growing area possible. Natural CO2 production, in particular, is a good choice in this day and age. The ease of use and the reduced effect on the environment make the above options the green choice. They are also easy on your budget, and your plants will love you for it.