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Articles, Gardening

CO2 Enrichment & Plants

by Sunny Datko

The dry matter in a plant is made up of 90% carbon, hydrogen and oxygen. The majority content, which is carbon, is taken into the plant through carbon dioxide (CO2) available from the air.

The average air that we inhale contains 0.003-0.004% of carbon dioxide. Carbon dioxide is an odorless, non-flammable, colorless gas.  It is believed that the prehistoric plants that developed eons ago had environmental conditions with very high levels of carbon dioxide in it. In today’s plants, due to their evolution, these more modern incarnations have maintained their capacity to harness more CO2 than the current environment now has.

Science has shown that high energy plants have the ability to consume PPM levels of 1200-1500 and in some cases even as high as 1750 parts per million; the average air we breathe contains 300 parts per million. So, as you can see, high-energy plants in the right conditions can consume much more than nature is currently providing.  The following graph will show what CO2 depletion and enrichment does to plant growth.

co2 enrichment in your garden or greenhouse

Below 200 PPM, plants do not have enough CO2 to carry on the photosynthesis process and essentially stop growing. Because 300 PPM is the atmospheric CO content, this amount is chosen as the 100% growth point. You can see from the chart that increased CO2 can double or more the growth rate on most normal plants. At rates above 2,000 PPM, CO2 starts to become toxic to plants and above 4,000 PPM it becomes toxic to people.

The consumption levels of CO2 that the plant needs are also directly correlated to lumens that they are subjected to (i.e. the greater the intensity of light, the greater levels of CO2 that the plants can consume, the greater the plants become).  Again it is not widely known that a plant saturated in light will only grow to be as big as the CO2 levels in that particular environment.  In other words, you might have all the light a plant could ever want, however, if the plant is only receiving a little CO2 then most of the light available to the plant is simply going to waste and is not available for consumption via the plant, as it cannot utilize the CO2 to photosynthesize the light.

When growing in greenhouses and indoor gardens, the need for CO2 generation is drastically increased. If a plant is growing in a sealed room without any additional fresh air or CO2, it will eventually use up all of the CO2 in the area.  Without CO2, photosynthesis comes to a halt, and the plant will stop growing all together.  Average high-energy plants in an average lit grow room with no in or output fans will consume the available CO2 within that grow room in a few hours. So any growth after all the CO2 has been utilized will slow completely down to a snail’s pace.

The uptake of CO2 is only necessary during the lighting cycle; plants do not require CO2 during the night cycle when the lights are off. Plants, like humans, do breathe out CO2, however, during their daylight cycle, the plants utilize the CO2, manufacturing sugars to feed the plants and so during the day cycle appear to only breathe out oxygen.

In order to fully benefit from CO2 enrichment, all of the environmental parameters must be well managed. It is important to perfectly master your plants’ needs on every level—temperature, relative humidity, lighting, CO2 concentration, etc. The moment one of these parameters is no longer ideal; it becomes an obstacle to plant growth. In a garden enriched with CO2, it is important to consider that the best temperature for plants will be slightly higher than usual. With proper CO2 enrichment, plants can reach optimal levels of photosynthesis that produce maximum growth and yields.

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