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

As you are probably already aware, CO2 (carbon dioxide), is a gas that is in our atmosphere. Although excess levels of CO2 are harmful to humans, the gas can help boost your marijuana yield because it enables plants to finish the process of photosynthesis (where plants convert carbon dioxide into energy).

Although results may vary, many growers suggest that adding CO2 in the grow room will increase your yield by up to 20%. As the name and formula suggest, CO2 is made from one carbon atom and two oxygen atoms. This is important because, while plants need a total of 17 essential elements to grow and reproduce, hydrogen, carbon, and oxygen make up 95% of a plant’s dry weight.

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?

In your marijuana plants,the stomata are the pores your plants breathe through, and it is through these that the weed extracts carbon dioxide from the atmosphere. During the process of photosynthesis, your plants extract the CO2 from the atmosphere. It is a process used by algae, specific bacteria, and plants, to use sunlight and turn it into chemical energy.

When you grow indoors, your cannabis plants use the light from the light bulbs instead of sunlight, and they 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, as long as you supply enough light.

Although lighting is important, you won’t get the best results unless you increase CO2 levels. If your plants were placed in a room with a lack of CO2, they would ultimately suffocate and perish. If you are using fluorescent lights or another low-powered source of light, there should still be enough CO2 in normal air to ensure your weed grows properly. You will not see an increase in yield if there is already enough CO2 in the air 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. When you force your plants to produce extra energy from the same amount of light, you are rewarded with a boost in growth and an increase in yield size.

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

Pros and Cons of Using CO2 Systems for Cannabis

First and foremost, don’t go down this route unless you are an experienced grower who knows how to grow a healthy cannabis garden with premium grade bud. Make sure you also know how to:

  • Use high-quality growing mediums and nutrients.
  • Use top shelf strain genetics.
  • Use 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 have maximized the other limiting factors such as light exposure, CO2 could provide a 20%+ boost in the size of your yield, while also increasing the grow rate of the plants by a similar amount.
  • Security: As long as you seal your room, CO2 can provide a much-needed security boost because no smelly air is being vented out. If you use a CO2 generator, it will create ‘natural’ smells that cover up the tell-tale 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 1200-1500 ppm (parts per million).


  • It is expensive: The process of injecting CO2 into a grow room is a costly one, especially if you are running a large operation. The cheapest methods of adding CO2 are also the least effective, but 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 because high levels of carbon dioxide are harmful to humans.

If you are happy to pay the money and are not concerned by the cons, the final step is to ask yourself a few questions. If the answer to all of the following is ‘yes,’ you can begin the process of adding CO2 to your grow room:

  • Have you maximized the amount of light your plants can use with your existing grow lights?
  • Are you sure that you have eliminated all issues from the grow room, including bugs and nutrient deficiencies?
  • Do you know how to use growth control methods to increase yields?
  • Are you able to keep the grow room’s temperature between 85- and 95-degrees Fahrenheit?
  • Are you able to keep humidity levels at 70% during the vegetative stage, and 60% in the flowering stage?
  • If you can increase the CO2 level in your grow room to 1500 ppm, are you ready to seal the area?

How to Introduce Additional CO2 to a Garden

There are numerous ways to add carbon dioxide to the garden, but 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 you find that the following two options are beyond your price rage, steer clear of other systems until you can afford a generator or compressed CO2.

CO2 Generators

Carbon dioxide generators look a bit like patio heaters and produce the gas you need by burning natural gases 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 to maintain a grow room of 800 cubic feet.

You can set up your CO2 generator to automatically power on or off when carbon dioxide levels reach a pre-set level. It should be easy to find liquid propane or natural gas generators, but when you burn these gases you end up with heat that’s tough to regulate in a small grow room. As a result, we believe you should only use a CO2 generator 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 to7%. 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 be able to 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, then compressed into tanks. As a result, you can introduce a controlled amount of carbon dioxide into the grow room without the need to purchase a generator. Therefore, you are not producing heat when releasing the gas, so there are no temperature and 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 a length of 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 the gas via respiration at night, it is common for CO2 levels to exceed 600 ppm by the following morning. When you set the timer to start dosing CO2 about 60 minutes after the lights come on and set the last dose 60 minutes before the lights go off, 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 terrible odor during the fermentation process. Also, it will only increase CO2 levels marginally.


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, it isn’t easy to grow the fungus correctly, even though its manufacturers claim you don’t have to do anything. 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. You have to add the ice manually every day, and it is hard to regulate the amount of CO2 in the air. Finally, as it must be used immediately, you must constantly 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 405 ppm, 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., published in the official journal of the Committee on Space Research in November 1994, showed that plant growth is increased even when CO2 levels approach 10,000 ppm!

Although 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 put your health at risk because a carbon dioxide 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 carbon dioxide can damage your plants.

Ideally, the CO2 that gets emitted should fall from above your crop because the gas is heavy and sinks to the ground. You can also use fans to keep the gas moving around the room so that your entire crop sees the benefit. It is important to note that in a tightly enclosed area, ambient carbon dioxide gets 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, and if it drops to under 100 ppm your plants will cease growing. Conversely, CO2 above ambient levels boost plant growth. Once your grow room is filled with air that has CO2 at a level of 1200 ppm or above, not only do you experience a boost in yield (some growers claim a 50% increase), but the fruiting and flowering time is reduced by up to 10 days.

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 and 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. If you allow stagnant air into the room, it can form a vapor barrier on the lower surface of leaves which inhibits intake of carbon dioxide.
  • Add humic and fulvic additives because they boost the intake 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 it uses nitrogen’s ammonium form efficiently.