How to Use CO2 to Increase Your Cannabis Yields [Guide]

Did you know that too much carbon dioxide (CO2) is potentially harmful to your marijuana plants? Or that if your plants don’t receive enough CO2, it can harm them too? CO2 is a crucial aspect of growing marijuana, one that can help, hinder, or halt your plant’s progress. When it comes to providing your plants with additional CO2, there are several things to keep in mind.

First, you need to ensure that your plants receive a CO2 level of above 250 parts per million (ppm).

Any CO2 level below this measure is harmful to them. Conversely, if your plants are exposed to dangerously high CO2 levels, they can die.

Why else is CO2 essential when it comes to growing marijuana? It enables plants to finish the process of photosynthesis. Photosynthesis is the process by which plants convert carbon dioxide into energy.

As the name and formula suggest, CO2 is made from one carbon atom and two oxygen atoms. This is important because while plants need 17 essential elements to grow and reproduce, hydrogen, carbon, and oxygen make up 95% of a plant’s dry weight.

Many growers suggest the addition of CO2 in the grow room could increase your yield by up to 20%. In this guide, we show you how to introduce CO2 to your grow room correctly for an outstanding end product.

How Do Plants Use CO2?

co2 for plants

The stomata are the pores in marijuana plants. It is through these that the plant extracts carbon dioxide from the atmosphere. During photosynthesis, plants extract CO2 from the air. Algae, specific bacteria, and plants use this process to absorb light energy before turning it into chemical energy.

When you grow indoors, your cannabis plants use the light from the light bulbs instead of sunlight. They absorb this artificial light and use it to produce sugar and oxygen. While the oxygen gets released back into the atmosphere, the plant uses the vital sugars to grow. When you boost the CO2 levels in your grow room, your plants create additional energy. That is, as long as you supply them with enough light.

Although lighting is essential, you won’t get the best results unless you increase CO2 levels. If your plants were placed in a room without CO2, they would ultimately suffocate and perish.

If you use fluorescent lights or another low-powered source of light, there should be enough CO2 in the air for your weed to grow. You will not see an increase in yield if there’s already enough CO2 in the atmosphere and you add more.

The situation changes if you are using more light than your cannabis garden can utilize naturally. In that case, adding extra carbon dioxide is worth your while because it will result in increased photosynthesis.

By causing your plants to produce extra energy from the same amount of light, you then notice a difference. This small measure should reward you with a boost in growth and an increase in the overall yield size.

CO2 also increases your crop’s resistance to heat and light stress. However, it is an expensive process, so there are a few considerations to account for before investing.

Pros and Cons of Using CO2 Systems for Cannabis

We wouldn’t advise you to go down this route unless you are an experienced grower. This information is for seasoned growers who know how to grow a healthy cannabis garden with premium-grade bud. Make sure you also know how to:

  • Choose high-quality growing mediums and nutrients.
  • Use top-shelf strain genetics.
  • Opt for a high-powered lighting system.
  • Grow in a sealed and secured room.
  • Prevent or treat diseases and pests.

If you meet the above criteria, keep reading to learn how to use CO2 to increase cannabis yields. However, you should also be made aware of the pros and cons.


You already know and understand the benefits, but here’s a reminder:

  • Faster Growth & Bigger Yield: Once you maximize the other limiting factors, such as light exposure, CO2 could provide a 20%+ boost to your return. It may also increase the grow rate of the plants by a similar amount.
  • Security: If you seal your room, CO2 can provide a security boost because no smelly air is vented out. If you use a CO2 generator, it will create ‘natural’ smells that cover up the telltale weed scent.
  • You Can Increase Grow Room Temperature: You can increase the temperature to up to 95 degrees Fahrenheit if you maintain a CO2 level of 1200-1500ppm.


  • It Is Expensive: The process of injecting CO2 into a grow room is a costly one, especially if you’re running a massive operation. The cheapest methods of adding CO2 are also the least effective. However, they can at least show you the potential of adding carbon dioxide. On the plus side, most of the cost comes from the start-up equipment.
  • You Need Strong Grow Lights: You won’t get adequate results if you use CFLs or T5s. Instead, we recommend using powerful LED lights or invest in an MHor HPS setup.
  • You Have to Seal the Grow Area: If you are trying to boost CO2 levels to over 1000 ppm, you need to seal the room. You must do that as high levels of carbon dioxide are harmful to humans.

How to Introduce Additional CO2 to a Garden

There are numerous ways to add carbon dioxide to the garden. However, many of them don’t provide a guarantee that the ppm will be delivered in a controlled fashion. As a result, we recommend investing money to ensure it is done correctly.

If these two options are too expensive, avoid other systems until you can afford a generator or compressed CO2.

CO2 Generators

Carbon dioxide generators look a bit like patio heaters and produce CO2 by burning natural gas or propane. When this happens, the exhaust fumes created are made up almost entirely of water vapor and carbon dioxide. If you use a generator with one burner, it should produce enough CO2 for an 800 cubic feet grow room.

CO2 generators can be set up to automatically power on or off when carbon dioxide levels reach a pre-set level.

Liquid propane or natural gas generators should be easy to find. However, burning these gases produces heat that’s difficult to regulate in a small grow room. As a result, we believe a CO2 generator should only be used in a large space.

Just imagine your grow room is 10 x 10 x 10 feet. On average, a CO2 generator will increase the temperature by up to 5 degrees, and the humidity will rise by 7%. If you are already having trouble keeping temperature and humidity in check, the generator could cause further issues. As a result, experienced growers only use generators in winter and prefer compressed CO2 in the summer.

Compressed CO2

You should find compressed CO2 tanks at a hydroponics store or even in a home brewing or compressed gas store. The gas is produced by the manufacturer and is first collected and then compressed into tanks. As a result, you can introduce a controlled amount of CO2 into the room without needing to purchase a generator. And as you aren’t producing heat when releasing the gas, there are no temperature or humidity concerns.

A compressed CO2 tank is perfect for a small grow room. It should include a ‘doser,’ a pressure gauge, a flow meter, a timer, a solenoid valve, and tubing. Attach the doser to the tank and open the tank’s valve. Pre-set the flow meter and set the timer to open the solenoid valve for the requisite time.

Remember, photosynthesis only occurs when the lights are on, so set the timer to switch off at night. As plants release CO2 via respiration at night, it’s common for levels to exceed 600 ppm by the following morning.

Set the timer to start dosing CO2 about 60 minutes after the lights come on. Then, set the last dose 60 minutes before the lights go off. This way, you will provide your grow room with enough CO2 in an economical fashion.

Other Methods of Adding CO2 to Your Grow Room


This involves using natural processes to produce carbon dioxide. Although it is a cheap and relatively easy method, it typically causes a foul odor during the fermentation process and will only marginally increase CO2 levels.


The composting process produces a small amount of carbon dioxide but is smelly and unsanitary. When you use homemade compost, it is hard to tell if you’re even adding enough CO2. There are also a number of pre-made compost systems, but they are expensive. If you’re going to spend money, you might as well save up for a generator.

CO2 Bags

These bags use fungi growing on organic matter to produce CO2. However, despite manufacturers claiming that you don’t have to do anything, it isn’t easy to grow the fungus correctly. Also, you need at least four CO2 bags in a small grow space for the ppm to increase noticeably.

Dry Ice

Dry ice is made of solid and cold carbon dioxide. When it warms up, it releases the gas into the air. Although it is an effective short-term method, it isn’t a good idea for long-term use because of the cost. The ice has to be added manually every day, and it’s tricky to regulate the amount of CO2 in the air. Finally, as it must be used immediately, you must continuously return to the store to buy it.

How to Use CO2 in Your Marijuana Garden

Today, CO2 levels in the atmosphere are at an average of over 400 ppm. This is the highest recorded level in over 800,000 years! For reference, the average level was a little above 330 ppm in 1980.

A study by Bugbee et al. showed that plant growth increases even when CO2 levels approach 10,000 ppm! While this is great news for cannabis, humans beware! Once CO2 levels exceed 3000 ppm, it becomes dangerous, and levels of over 5000 ppm are deadly.

Fortunately, you don’t have to risk your health. A CO2 level of between 1200 and 2000 ppm is more than enough to experience a boost in yield. However, if your cannabis garden doesn’t generate the requisite levels of light and heat, excess CO2 can damage your plants.

Ideally, the CO2 source should be placed above your marijuana plants. The reason for this is that CO2 is heavy and sinks to the ground.

You can also use fans to keep the gas moving around the room, benefiting your entire crop. However, in a tightly enclosed area, ambient carbon dioxide is used very quickly.

For instance, in a plastic greenhouse, CO2 levels can plummet to under 200 ppm just 60 minutes after sunrise! Once CO2 levels become that low, plant growth suffers. If it drops to under 100 ppm, your plants will cease growing.

Conversely, CO2 above ambient levels boosts plant growth. A grow room filled with a CO2 concentration of 1200 ppm or above is a must. In these conditions, you should experience a boost in yield (some growers claim a 50% increase). Another bonus is that the fruiting and flowering time can be reduced by up to 10 days too.

Final Quick Tips on Increasing CO2 Levels in Your Marijuana Garden

  • Consider using air-cooled lights with glass inserts. Approximately 50% of the heat is removed from the lights before they enter the room. Also, by using sealed glass, you reduce CO2 loss to negligible levels.
  • Please ensure that the relative humidity level is between 40% and 60%. If the level goes too low, the stomata of the plant will close.
  • Purchase dehumidifiers and recirculating air conditioners. When you use exhaust fans that cycle regularly, you end up wasting CO2.
  • Oscillating fans are a sound investment because they improve air movement. Stagnant air can form a vapor barrier on the lower surface of leaves, which inhibits the intake of carbon dioxide.
  • Add humic and fulvic additives because they boost the absorption of iron and several other elements. Iron acts as a catalyst for chlorophyll production and enhances the process of photosynthesis in high CO2 conditions.
  • Try to increase the ratio of ammonium to nitrate in your fertilizer. When CO2 levels are high, plants don’t assimilate as much nitrate-nitrogen, but they use nitrogen’s ammonium form efficiently.
Cultivation Techniques
Join The Discussion

By clicking "Post Comment” you agree with our Terms of Use and Privacy Policy

    TOC Protection Status © 2000 - 2024 All Rights Reserved Digital Millennium Copyright Act Services Ltd. |

    WayofLeaf use cookies to ensure that we give you the best experience on our website. If you continue to use this site we will assume that you are happy with it. More Information