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Everything Growers Should Know About Using CO2 in Their Growing Rooms

Mar 11, 2020
Setting Up your Grow Space

Everything Growers Should Know About Using CO2 in Their Growing Rooms

Inevitably, a grower comes to the point of having to decide whether or not to introduce supplemental carbon dioxide (CO2) into their growing environment. Cannabis enrichment systems range from primitive to sophisticated, and from cheap to expensive. Growers of all sizes boost the CO2 content of their growing environments to use their space more efficiently via the sped up growth and increased yields that subsequently occur. Here is what every cannabis grower needs to know about using CO2 in their cannabis growing rooms.

 What is CO2, and Why Does It Matter?

C02 is a colorless, odorless, and invisible gas. It has no taste. It naturally occurs in small concentrations in the Earth’s atmosphere. Cannabis plants can’t survive without CO2 any better than humans can without oxygen. CO2 is the by-product of mammalian respiration, and it is a marijuana plant’s jam.

Carefully managed CO2 supplementation increases the overall yield of a cannabis harvest. Although it comprises but a minute part of the Earth’s atmosphere, in its concentrated form it is heavier than air. As a result, CO2 continuously moves in a downward direction. Growers must consider this characteristic of CO2 when contemplating their CO2 enrichment plan.

Increased CO2 Does Not Equal More Potent Pot, but Faster Growth

Growing operations of all sizes can make use of supplemental CO2. This is not in question. The question is whether it benefits the grower to supplement with CO2. Never invest time and money into a CO2 system for your growing environment unless there are certain benefits. Novice growers sometimes think additional CO2 will give them a more potent crop, but this isn’t the case. CO2 has no effect on pot potency. High-THC seeds from a reputable seed bank will yield high-potency buds.

Instead, CO2 enrichment makes cannabis plants grow around 30% faster. Increased atmospheric CO2 allows plants to transform CO2 into glucose and oxygen. Photosynthesis occurs when a plant containing chlorophyll combines with sunlight in the presence of CO2 and water. The plant takes the CO2 waste product of animal respiration and transforms it into life-giving glucose and oxygen. CO2 basically speeds up the process of photosynthesis by saturating all the enzyme’s active sites so that growth can happen at maximum speed.

 Reasons Growers Use CO2 Enrichment

These actions by the plant benefit growers in different ways. The primary reason most commercial growers use CO2 is that they have a limited amount of space in which to grow their crops. By hastening each cannabis crop with supplemental CO2, year-round growers can fit an extra crop in their annual rotation without having to expand the size of their facility. At the end of the year, even one extra crop means more profit.

Because CO2 is a naturally occurring substance, it is available at a fairly low cost and has virtually no harmful side effects when used in moderation. Even if added in vast excess, all that happens is the cannabis plants leaves may become thicker, rendering them less efficient for running photosynthesis energy production. When added in excess of 2000 ppm, you would likely be subjecting your plants to negative stress, and most certainly be ‘throwing away’ your money.


 Not All Growers Need or Want Added CO2

Outdoor growers, and indoor growers with plenty of time, space, and no fear of snoopers, have little interest in supplementing with CO2. They have little interest in the ‘faster is better’ business model. They’ll end up with approximately the same thing as their less-patient peers, but it will take longer. These growers don’t care. They have nothing to gain by hurrying their crop, and they are unwilling to spend the money for a C02 enrichment installation that provides no benefit to their operation. Perhaps instead they will stick with seeds that inherently have a faster flowering time in that particular strain.

The only growers who benefit from added CO2 are those who desire a larger crop in a shorter amount of time. The additional CO2 causes plants to grow heartier stems and larger fan leaves. Larger leaves speed up photosynthesis, which completes the cycle by hastening plant growth even more. Only growers who find some significant benefit in bringing their crops to harvest more quickly need to consider enriching their growing environment with CO2.


 Don’t Fear Global Warming: Plants Love CO2

The CO2 content in normal air ranges from between 0.0300 and 0.0400 parts per million. This amount sustains the Earth’s plants, although they would thrive abundantly were more CO2 available to it. Weather alarmists worry about global warming because of increased CO2 in the atmosphere. If people plant enough trees, cannabis, and other CO2-consuming plants, then soon the world’s fears about global warming will evaporate like the dew.

With other factors being equal, plants thrive in open systems – when ventilation and exhaust systems are in place to circulate fresh air. Plants in closed growing environments initially thrive, but become increasingly stressed as they deplete their supply of CO2. Plants with ample CO2 grow and thrive instead of spending all their energy to survive. Unless they receive supplemental CO2, they will die.

CO2 Is Part of the Good Cannabis Recipe

Growing good cannabis products is akin to baking a cake. Butter, sugar, eggs, flour, and milk are ingredients that when mixed in the correct proportions and baked, produce a cake. Should the cook leave out even one ingredient, the cake would be a colossal failure. It is the same with cannabis. It is easy to produce high-quality marijuana as long as you follow the formula. Be warned that you will kill your plants if you leave out even one ingredient from their recipe.

Humans will notice the ill effects of too much CO2 in the atmosphere long before it affects cannabis plants. There is no need to use more CO2 when enough is sufficient. In other words, plants will not grow in direct proportion with the amount of CO2 they receive. With CO2 supplementation, less is more. Although excessive amounts of CO2 don’t appear to harm plants, neither does it benefit them beyond a certain point.


 Meeting the Prerequisites

Here are the primary questions growers must ask. What prerequisites must a grower meet before considering adding CO2? These are the concerns that render supplemental CO2 irrelevant. Why? Because if the prerequisites aren’t taken care of then the crop inevitably dies without them. Ask yourself these questions: Does your growing space already provide all that you need in terms of adequate light, airflow, and growing medium? Have you tested your soil to determine what it needs? Soil considerations come before CO2 considerations. The seal on growing spaces must be tight for the plants inside to enjoy the full benefit of supplemental CO2. Is yours?

Growers in the planning stages of their operations foresee their need for CO2 and plan accordingly. All indoor growers should own a CO2 monitoring system, or at the very least a handheld CO2 monitor. With this tool they gain the ability to track ambient CO2 levels. This data allows growers to make an informed decision about adding CO2 into their closed growing environments. Growers must know how much CO2 is present before they can estimate how much CO2 to add for the health of the plants.

Ways to Add CO2

There are at least three primary ways to introduce CO2 into a cannabis growing space. They each have pros and cons, and what is right in one grower’s setup may be irrelevant in another’s. The size of your operation mainly determines the method to use. The three methods of generation CO2 are:

  1. Chemical Reactions. CO2 results from the combination of certain reactive substances. For example, vinegar and baking soda produce a temporary reaction that results in the release of CO2 gas when mixed. Sugar and yeast mixed with a little water likewise temporarily boost the CO2 present in their immediate atmosphere. A naturally occurring chemical reaction takes place when mushroom cultures eat through their substrates.


Mushroom bags are commercially available to hang above plant canopies to increase CO2 in enclosed spaces. These methods have the advantage of requiring no electricity, but are only practical for small growing areas. The disadvantage is that growers have little control over the exact amount of CO2 these reactions produce, and methods that require mixing and constant replenishment are labor intensive.


  1. Compressed Air. CO2 is available to growers at gas companies, hydroponic stores, paintball and brewery support stores in refillable tanks. Tanks of compressed CO2 come in different sizes, to better meet each individual grower’s requirement. For example, growers using a 5’x5’ tent may need little more than a small canister. Growers in remote locations who operate without electricity favor larger canisters as they last longer.


Large operations that use compressed CO2 buy canisters in bulk. This limits potential interruptions to the growth they expect. When one tank empties, they roll out another.  These tanks can also be heavy, so getting them high enough to dispense above the marijuana plant canopy is problematic. Growing spaces using CO2 must have a plan for circulating the CO2 within the room. Compressed CO2 with a manual controller allows the grower greater awareness of how much gas is released and when. No heat is generated with this method and doesn’t require the use of a generator. Canister CO2 dispersion is good on a small scale, but impractical for most operations larger than 10 x 10 feet.


  1. CO2 Generators. A CO2 generator is the best way to go in large growing spaces. A CO2 generator largely automates the delivery of the gas. Pipe CO2 into large growing houses via CO2 generators. The generator hooks to an overhead system that dispenses the gas via specially designed pipes or hoses. Natural gas or propane supply companies provide energy to these systems for a continuous and uninterrupted fuel supply.


The design of CO2 generators enables them to dispense just the right amount of CO2 to bring a growing space’s CO2 percentage up to the desired range. Just what makes up the perfect range is a topic of great debate among growers, however the majority report success in the 800-1500 ppm range. Whether seedlings benefit enough from supplemental CO2 to be worthwhile is a topic debated among growers. Most growers agree that plants in the vegetative stage enjoy the enhanced growing atmosphere, and these plants flower earlier.


Regardless of the means or the method a grower chooses for CO2 delivery, something that all growers who are using CO2 should always keep in mind is the importance of knowing when to stop. The time to stop is when you’ve achieved the predetermined level of saturation. Any additional growth realized is so negligible that it isn’t worth the increased cost of continuing with CO2 supplementation.


Timing and Effects

Growers adhere to a schedule when determining the most beneficial time to help their growing room atmospheres with CO2. Growers on a budget want to get the most ‘bud for their buck’ by adding CO2 when it makes the most difference. The second through fifth weeks of the flowering phase is when additional CO2 makes the most difference. Specific benefits associated with this window of opportunity include increased stem strength, an essential requirement necessary to support the trichome-laden colas through their harvest.

Supplemental CO2 improves the rate of plant growth in a positive-feedback kind of system. Photosynthesis speeds up, which brings energy to grow more leaves. Now the plant has more leaves to run the process of photosynthesis! Plants that receive additional CO2 also become more water efficient. Transpiration is the process of water moving through the plant, up through the roots and distributes among the leaves for evaporation. This is something that growers with limited water resources may find helpful. Another reason to use CO2 is that it lets plants tolerate a higher temperature than their normally ideal temperature of 70°, something that potentially works in favor of many growers.

In conclusion, growers that install supplemental CO2 systems get the most from their investment if they take the time to properly monitor their results. It is through the collection of data and the analysis of the results that determine whether the additional CO2 was helpful. Document how much you spent, how many days earlier the crop came to fruition than in previous years, and whether over the course of the year you saved any time. Time is the primary fruit that CO2 buys. It also buys more space for the grower in the sense that it lets him or her turn over crops faster making room for another harvest. Money doesn’t really weigh in as a factor unless it is the grower’s aim to squeeze in an extra crop.

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