Plant growth is fueled by the production of glucose through photosynthesis. This process requires three components–water, light and carbon dioxide (CO2). In other articles, we address lighting and watering. Here, the focus is CO2 –specifically, how to supplement it.
Carbon dioxide enrichment can greatly improve the yield of indoor marijuana crops. Plants take in carbon dioxide (CO2) and release oxygen through holes in the undersides of their leaves called stomata (plural for stoma). Atmospheric CO2 content is typically somewhere between 300-600 parts per million (ppm). Presence of CO2 at this concentration has proven sufficient for every plant on Earth, from microscopic algae to towering redwood trees.
To maintain high growth rates, you will need to replenish CO2 by adding fresh air or by adding CO2 artificially. Elevating CO2 content to levels higher than what is found outdoors can result in growth rates that are impossible to achieve in nature. This is the reason many indoor growers choose to supplement CO2 artificially.
While you can supplement CO2 in a variety of ways, some methods are more cost effective than others. When choosing a CO2 enrichment method, the single most important factor is the size of your grow room. Following is an analysis of several of the available options.
You can purchase a chemical kit online or at your local grow shop. These kits work by combining non-toxic components to produce a chemical reaction that generates CO2. Chemical kits offer a finite return and are single use only, with each use spending one chemical charge. One manufacturer claims that their kit, housed in a bucket, can generate enough CO2 to enrich a 10′ x 10′ room by as much as 1600ppm. With a daily cost of $1.50 or more, these kits are probably best suited for smaller rooms.
Baking Soda and Vinegar
Some growers claim to get increased growth rates by mixing these two common household products. This technique is strictly a D.I.Y. enthusiast’s approach, and offers very little CO2 in return. Gas is produced in an instant release, and has very little lingering effect. This chemical reaction does produce CO2 but is not cost effective. Leave this one for volcano experiments.
Fermentation, Composting and Yeast
The natural process of fermentation and decomposition produces carbon dioxide in measurable quantity. Some enthusiasts have attempted to harness this process for CO2 enrichment. Both of these natural sources of CO2 can be used by indoor growers. Yeast may be a better source of CO2 than baking soda and vinegar because it generates CO2 for a longer duration and can be reactivated by adding more sugar. Unless you are a brewer or a baker, do not expect much benefit from this method. Such a system may prove useful for those with very small rooms, closets or grow cabinets.
Bottled Carbon Dioxide
You can purchase filled tanks of CO2 from your local welding supply store. Tank systems make use of a regulator and an electric solenoid that controls the release of CO2. When in the open position the solenoid permits gas to escape the bottle and travel into a thin perforated tube called a halo. The halo is positioned over the plants and serves as a diffuser. The heavier-than-air CO2 then flows down over the plants. Tank systems can be automated with either a CO2 sensor and controller or a repeat cycle timer. Bottled CO2 enrichment offers a heat-free alternative to propane burners, but may be cost prohibitive for larger rooms.
Propane and Natural Gas CO2 Generators
These heater-like units produce carbon dioxide by burning propane or natural gas–both relatively affordable resources. This method raises the issue of heat management in grow rooms, due to abundant heat and humidity–by products of burning hydrocarbons. Even so, such combustion CO2 generators are the most practical and cost-effective method of enriching large rooms or greenhouses.
Exhaust from gas hot water heaters can be routed into grow rooms to achieve CO2 enrichment. This method can generate CO2 at no additional cost, in homes with propane or natural gas water heaters. Enriching in this manner can be dangerous, leading to excessively high CO2 levels and asphyxiation. Moreover, old malfunctioning hot water heaters can produce lethal carbon monoxide. For this reason, I do not recommend the use of appliance exhaust gas as a means of enriching CO2 levels . Should you choose to do so, be sure to take every precaution not to kill yourself or others.
Carbon Dioxide: Fertilizer For The Air,