There are two reasons to supplement your sealed grow space with additional carbon dioxide (CO2): CO2 enables plants to produce greater yields and to grow faster. Increasing CO2 levels during the vegetative stage and the first two to three weeks of the flowering stage should maximize your yields if all other growing conditions are ideal. The practice of supplementing a cannabis grow with CO2 is widely accepted in the cultivation community, but if you are a novice grower, this might be your first time hearing about it. Here's more about the science behind this practice and a guide to how you can do it yourself.

Continue Reading Below

How Plants Use CO2 To Grow

Humans and plants need each other to survive. Humans inhale oxygen and exhale carbon dioxide.  Plants intake carbon dioxide and release oxygen.  Plants “breathe” in CO2 through small pores located on their leaves called stomata. This begins the process of photosynthesis. Photosynthesis Illustration The combination of water, CO2, and light allow plants to create energy. During this process, plants combine the carbon dioxide extracted from the air with the water the plant intakes through its roots. Light catalyzes a chemical reaction between the water and CO2 that produces oxygen and C6H1206, a substance similar to glucose which the plant uses for energy.

Plants that grow outside usually receive more than enough CO2, and when they are in ideal conditions they are able to produce excess food, which they store in other parts of the plant. When it comes to cannabis, the additional food creation produces a greater yield in a shorter amount of time.

Things to Consider Before You Add CO2

The potential benefits provided by CO2 may make supplementation seem like a no-brainer. However, growers should make several considerations before they begin adding the molecule to their gardens.  Added CO2 will only benefit healthy plants. Since the best CO2 injection practices require a significant amount of time and money (particularly at the front end), growers should be certain that their gardens are ready for the addition by dealing with all other yield-limiting factors.

Plants with weak root systems will die even if they are given additional CO2. Healthy root systems require adequate aeration so that they can use oxygen and uptake water and nutrients. That means that the growing medium the root system is immersed in should not be overwatered or dehydrated. Pesticides and pests must be controlled in order for CO2 to work its magic.  Unless those predators are dealt with, a cannabis plant will either struggle to thrive or die. Pesticides have to be controlledChemical solutions can be damaging to the environment, the plant, symbiotic members of a natural ecosystem, and cannabis consumers. There is a host of natural and chemical-free pest control options to ward off and kill plant predators. Plants suffering from a nutrient burn or deficiency will not benefit from CO2 supplementation.

When using chemical fertilizers, it is possible to provide cannabis with too many nutrients. As with humans, a nutrient overdose is poisonous to the cannabis plant. There are natural ways of fertilizing plants that require more maintenance but that come with much less risk. It’s also important to monitor your plant for nutrient deficiencies, as these will make it impossible for the plant to remain healthy.

Unless there is sufficient light, additional CO2 will be wasted. As explained earlier, photosynthesis requires the combination of water, light, and CO2. A strong light source such as HPS or LED lighting will do the trick. A good ratio to keep in mind when determining the amount of light per square foot in your grow space is 7500-10000 lumens/square foot. Increased CO2 levels will also result in increased humidity.  To protect your plants from the dangers of excess humidity, invest in a strong dehumidifier. Finally, it's important that you seal your grow space so that CO2 does not leak out of the room.  That is especially true if your grow space and living space are connected.  Concentrated levels of CO2 can be dangerous for humans, so make sure that you aren’t breathing it in or letting it seep into your home.

Continue Reading Below

The Best (and Worst) Ways to Increase C02 in Your Cannabis Grow 

First and foremost, it is important to set up your CO2 in such a way that it is falling onto your plants from above. CO2 is heavy, so it will sink to the bottom of the room. To keep it circulating, install fans facing upward so that the CO2 never fully hits the floor. The most recommended methods of CO2 supplementation are the use of a CO2 generator or compressed CO2. A generator creates a lot of heat, so it works best in large grow areas. Compressed CO2, on the other hand, does not add much heat, so it is the best between the two options for a small grow space.

Other best practices include turning your CO2 off at night; plants don’t photosynthesize without light. Another factor to consider is the installation of climate controllers and timers. These automated systems will assist growers in managing humidity, temperature, and CO2 levels. Though these systems can be expensive, the convenience and assurance they provide make it a worthy investment.

Alternative Ways to Add CO2 to Your Garden

There are cheaper and seemingly more convenient ways to boost CO2 levels in your grow space.  Breathing on your plants, for example, is free.  However, it is unlikely that simply breathing on your plants will produce enough CO2 to get the kind of results that growers are looking for. Some also use methods that require an open flame such as a Bunsen burner. This type of CO2 generation is very difficult to monitor, so growers won’t know how much or how little CO2 is actually released. Moreover, this an extremely dangerous option since indoor grows are already warm and full of electrical wires and water. The risk of fire or explosion outweigh the benefit of CO2 generated from these methods.

Is It Beneficial to Add CO2 to an Outside Garden? 

The natural ventilation provided by the atmosphere provides plants with the ideal amount of CO2. Additionally, dispersing CO2 into an outdoor grow would be extremely difficult to control and the cost of that variability would more than likely outweigh the benefits. The only way to control CO2 levels is to seal the grow space, so using CO2 in a tent or greenhouse can harness CO2 to maximize “outdoor” (or almost outdoor) yields.