Mild temperatures, light, water, and nutrients, are part of plants' requirements for photosynthesis, but people often forget the crucial role of CO2. Let's examine this often misunderstood aspect of indoor and greenhouse growing, writes Joy King with Growlink.

Typical ambient CO2 levels outdoors comprise 0.04% of the atmospheric volume of about 400 ppm. Plants take up CO2 by diffusion through tiny pores called stomates located on the underside of leaves. The opening and closing of stomates are influenced by leaf and air temperatures, humidity, light levels, water stress, CO2 concentration, and oxygen in the air and leaf. If any environmental or cultural factors used for photosynthesis are limited in an indoor farm or greenhouse, plant growth and yield are compromised.

Why you should consider supplementing CO2
Until more recently, most growers in the U.S. did not measure CO2 or use it to improve crop growth. CO2 levels can suddenly become limited during winter, especially in unventilated greenhouses on cold and sunny days. Over the past ten years, greenhouse growers have sealed their greenhouses to manage heating bills, with the negative side effect of reducing CO2 levels within the grow.

The more CO2 and PAR plants get, the faster they photosynthesize, grow, and produce flowers and fruit. Growers with supplemental lighting and a tightly sealed growing environment may not realize the full benefits of their investment if CO2 levels are too low.

How to monitor and control CO2
A CO2 meter is needed to both monitor and controls CO2 supplements. Available in a myriad of versions, computer-controlled sensors vary in their level of refinement and precision. Sophisticated controllers can inject CO2 from compressed or liquid sources or turn CHPs on or off. 

What can you do to increase CO2 in the greenhouse?
There are various ways to enrich CO2 in the greenhouse and indoor cultivation facilities. Carbon dioxide can be released under the crop canopy in greenhouses via small, inflated tubes. Growers can also use CHPs for CO2 enrichment. 

Since photosynthesis of most plants occurs during the daylight hours, CO2 enrichment is not required at night (or lights out mode for indoor grows). It is typically recommended to provide CO2 enrichment when CO2 levels dip below ambient levels. For operations that want to enrich the CO2 levels above ambient levels, concentration no higher than 1,000 to 1,200 ppm is recommended when there is a lack of air circulation. CO2 enrichment should occur one hour after sunrise (or lights on) and end two to three hours before sunset (lights out) for best results. 

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