Cultivation Clinic: CO2 Can Increase Yields 40%

CO2 and Cannabis

When we talk about adding carbon dioxide to marijuana gardens, the science behind the theory isn’t specific to cannabis alone. All plants need CO2 to develop, grow and be healthy. However, with flowering plants such as marijuana, adding CO2 to a garden can greatly increase their yields. Over 90 percent of the dry matter in cannabis is carbon, hydrogen and oxygen, and the sole source of that carbon is the CO2 in the air.

It’s important to note that a plant needs and uses CO2 only during daylight hours. And the more light that’s made available to a plant, the more CO2 it needs for photosynthesis. It is in this process that the carbon-fixing reaction occurs, splitting CO2 molecules into carbon (C) and hydrogen (H) to create food for the plant in the form of sugars and starches.

CO2 is measured in ppm (parts per million). Ambient CO2 levels in the outdoor atmosphere average about 300 to 400 ppm, which is adequate for plants growing in nature. However, indoor marijuana gardeners can control the atmospheric conditions and sometimes choose to boost these levels in order to quicken plant development and pack weight onto their buds. Increasing the CO2 level from 400 ppm to as much as 1,500 ppm can increase plant growth by nearly 40 percent.

However, there is such a thing as too much CO2. Much like human muscles with steroids, cannabis plants that take in too much CO2 can start to have tissue- deterioration issues — and when flowering plants are pushed to these limits, the quality of the buds may start to diminish.

CO2 Garden Levels

Consider the following: In a California greenhouse, a plant in full sunlight at midday will receive approximately 5,000 lumens per square foot. At this light intensity, a cannabis plant can process up to 2,000 ppm of CO2. For 3,000 lumens per square foot, the plant can use up to 1,500 ppm. At 1,000 lumens per square foot, this amount drops to ambient levels of 300 ppm.

However, it’s important to remember that these guidelines use lumens as the benchmark, whereas PAR (photosynthetically active radiation) is the better standard for measuring the light-to-CO2 ratio in your garden. That’s because lumens measure all of the available light coming from the source, not the light that is actually used by plants. Light that the leaves cannot use (for various reasons) is completely wasted, as its photons don’t get absorbed and employed by the plant in the carbon-fixing process. Thus, it would be better to calculate the amount of CO2 that a garden needs using PAR as the standard of measurement. However, since PAR values within an indoor garden are difficult to ascertain (and specialized equipment is needed), a good rule of thumb is to keep indoor gardens around 1,000 ppm when supplementing your environment with CO2. This can increase garden yields by as much as 20 percent while also keeping potency high and quality intact.

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