How To Increase Cannabis Yields With CO2

Introducing carbon dioxide into your grow room for bigger yields is easier said than done. Although it is simple enough to buy and install, maintaining the right levels without hurting your cannabis plants is a challenge. High concentrations of CO2 can kill plants and more importantly, it can be extremely harmful for you if it is not managed correctly. This guide teaches you how to safely introduce CO2 into your garden so you can achieve heavier harvests without too much difficulty.

It should be noted that using carbon dioxide is recommended for advanced users who already have some experience growing. It is best to wait until you have got the basics learnt, understand your equipment and are already achieving decent yields. Just remember, CO2 is only for increasing volume, not for boosting potency or flavour. You can still produce satisfying harvests without additional CO2, so get that down first.

How Do Cannabis Plants Use CO2?

Carbon dioxide (CO2) is a naturally occurring gas and forms part of the air we breathe. CO2 is a fundamental part of our ecosystem and is one aspect of life that allows plants to live and produce oxygen. What most people don't know is how CO2 is used by plants. It would make sense to understand this area of biology before rushing to inject loads of CO2 in the grow thinking it will increase plant size.

Cannabis plants use CO2 in the process of photosynthesis. CO2 is absorbed through the pores in a cannabis plant's leaves. These are called stomata and are essentially where the gas exchange happens between the plant and the atmosphere, allowing the plant to 'breathe'.

CO2 is made up of one carbon atom and two oxygen atoms. During photosynthesis, the carbon atom is turned into sugar for the plant and the oxygen molecules are released back into the atmosphere via the stomata.

Increasing CO2 means more CO2 is taken from the air and converted into useable sugars, which means higher levels of energy for the plant. Naturally then, plants that have easier access to CO2 can grow bigger because photosynthesis increases. But only up to a certain point and only if there is enough light. Without the proper light, cannabis plants literally cannot inhale and exhale properly.

Pros and Cons of Introducing CO2

Before we dive in, let's quickly outline a few of the reasons why you may or may not want to introduce CO2 supplements into your grow room.

Types of CO2 Supplements

There are some different ways to introduce CO2 into your cannabis crops, however not all are as effective as each other. We've outlined the two reliable methods most growers opt for when it comes to CO2 injection. Usually, these are setup outside the grow space.

CO2 Generators

CO2 generators burn natural gas or propane, which produce a fume of carbon dioxide and water vapour. These are normally used in large spaces that do not heat up too easily. The reason being, CO2 generators have a tendency to increase temperatures quite substantially, as well as raise the humidity.

Tip: One of the benefits of using CO2 generators is their efficiency at masking smells. The burning of gases in the generator creates a unique smell which does a fairly good job of covering up the potent odor produced by cannabis plants.

Compressed CO2 Tanks

Using compressed CO2 tanks is a much more effective method of introducing the technique into your grow room. If you're looking for the easiest way to boost CO2 levels, this may be the way to go. CO2 tanks means you do not have to burn gas, which is quite a big hazard.

CO2 tanks can be found in most hydroponics or gas stores. Using a pressure gauge and controller, a compressed CO2 tank allows a more accurate control of the gases being released into the space. They are better suited to smaller grow rooms than CO2 generators because they do not interfere so much with temperature or humidity.

How to Increase Yields with CO2

Measured in parts per million (PPM), the carbon dioxide found in our atmosphere normally has a concentration of roughly 400PPM. Anything over 3000PPM can start to become harmful for humans. Plants need a minimum of 250PPM if they are to grow properly. On the other end of the spectrum (that's what you came here for), boosting CO2 to around 1200-1300PPM has shown that plants grow bigger and produce almost 15-20% more volume in bud. 

Bear in mind that boosting CO2 higher than 1500-2000PPM can really start to mess with the environment. Humidity levels are a common problem, especially as temperatures are likely to be above average in CO2 setup.

The grow room should be completely sealed if we are looking to maintain a stable environment and make best use of the CO2 without wasting energy. This is why it is recommended that the airflow is setup separately from the grow space. For example, you can use cool tubes on your lights to move hot, humid air out of the space quickly.

Note that the quality and intensity of the light received by your cannabis plants determines how efficiently they are able to photosynthesise. Adding CO2 increases photosynthesis if the light is powerful enough for the size of the space. At least 600W per 10x10 foot area should be enough to start with CO2 injection. HPS lamps work well in combination with supplemental CO2 because they produce plenty of light as well as heat.

1200WHPS CO2 MULTISTRAIN GROW

There is no point adding CO2 if there is not enough light and heat. Plants that receive too much CO2 and not enough light or heat are likely to suffer and it could even be fatal. Cannabis plants can deal with slightly higher temperatures when CO2 levels are increased (up to around 35°C), but underdoing (or overdoing) it can cause serious damage.

Remember, it is extremely important all other aspects of your grow are in check before considering CO2. Make sure you understand your strains well. Ensure your temperature and humidity levels are on point and you know how to control the environment. Once you're confident with growing and have the right equipment, it might be worth considering CO2 supplementation.

Grow Tips

Both generators and compressed tanks can be automated so the flow of CO2 is controlled and maintained at the correct level.

• CO2 is Heavy - Place your CO2 generator or tank in a place where you can easily feed the gas to the top of your grow space. CO2 is heavy and will fall, so with the right fans and air circulation you can distribute it evenly across your garden.
• Gradually Increase CO2 - Suddenly increasing CO2 levels may be harmful for your plants. Start at a low concentration and work your way up through flowering. 
• Use During Lights ON - It is not necessary to inject CO2 during the night because photosynthesis is not taking place. CO2 generally increases during the night anyway.
• Dehumidifiers - Increasing CO2 has the tendency to raise humidity to dangerous levels, so moisture control is advised. Dehumidifiers allow you to reduce humidity if levels become too high.
• Oscillating Fans - Circulating the air allows the CO2 to be more efficiently absorbed by the plants. Fans also help to decrease humidity and temperature, reducing the chance of mold.

Bubba Kush by Drowcc_Genetics from GrowDiaries

Conclusion

Although not for the faint hearted, adding CO2 can have amazing results if it is controlled correctly. If you have never grown before do not worry about CO2 injection as it is not necessary to grow top shelf cannabis. Even as an experienced grower it may seem like a leap, but it is worth the effort if you can afford it.

If you found this article useful, take the opportunity to share your opinion and experiences about CO2 in the comments section below.

External References

Passive CO2 Fertilization and Humidity Regulation for Photoautotrophic Micropropagation of Cannabis sativa L.. - Pepe, Marco. (2020). 

Strategies to Enhance Photosynthesis for the Improvement of Crop Yields. - Nölke, Greta & Schillberg, Stefan. (2020).

This article was updated October 2020.