How to Use Carbon Dioxide to Increase Cannabis Yields?

Carbon dioxide is all around us, but we don't use it. Your cannabis plant, on the other hand, relies on it for growth. So CO2 is to your cannabis plant what oxygen is to you.

CO2 is essential for cannabis plants to carry out the photosynthesis process. 

During photosynthesis, the plants convert CO2 to energy using light energy. And the higher the CO2 levels in your grow room, the better your plant grows, leading to a more significant yield. 

However, using CO2 to grow bigger plants with bountiful buds isn't as simple as opening a CO2 canister once every day in your grow room — you must add CO2 at the right levels at the right rate.

Introduce CO2 in your grow room correctly, and you will be rewarded with over 20% bigger plants and many bushy buds. In this article, we show precisely how to do that.

How Does the Cannabis Plant Use CO2?

The cannabis plant, like any other plant, extracts carbon dioxide from the atmosphere using tiny pores on the leaves. These pores are called stomata, used by plants to breathe.

And when your plant is in the light cycle, it uses the heat generated from light to convert CO2 into oxygen and glucose, described as the photosynthesis process.

Once the oxygen and glucose are extracted, the plant releases oxygen back into the air for us to breathe and uses the glucose for its own growth.

The average grow room atmosphere contains around 410 particles per million (ppm), which is more than enough for the plant to grow. However, if you want to grow bigger plants, you can introduce more CO2 into the grow room.

The plant utilizes more CO2 to produce more energy and grow itself even bigger. It would help if you still had the right lighting conditions, though. Otherwise, too much CO2 can choke your plant.

There are a few other considerations you must consider, but before we get into the details of it, let's answer some basic questions.

Should You Use CO2 to Get Bigger Cannabis Yields?

While you can use CO2 to produce bigger plants, it doesn't mean you should. More CO2 has various benefits for the plant, but the systems are expensive and meticulous. In addition, the process of introducing CO2 into your grow room is complex.

If you are a novice cannabis grower or have a small budget, we recommend using other yield-increasing methods before choosing CO2 to grow bigger plants. There are various simpler, cheaper methods to increase yield without making a hole in your wallet.

As a general rule of thumb, follow this checklist to know whether you are ready to use CO2 to increase your cannabis yields:

• You have grown healthy plants with potent, bushy buds previously
• You have managed to prevent (or cure) pest and mold infestations on your plants
• You use high-power lighting panels and proper nutrients and grow medium for your plants
• You choose tried and tested cannabis strains for cultivation
• Your grow room is sealed from the outside environment 
• You have enough money to invest in a CO2 system

If you check all the above pointers, you are ready to introduce CO2 into your grow room. 

CO2 is complex, and one wrong move can compromise your cannabis plants or hurt you. So, caution is always advised. In addition, the plants may need more nutrients when you add additional CO2. 

Okay, now that we got the warnings squared away, let's look at what CO2 can actually do to your plants. Adding more CO2 to any grow tent will stimulate more growth, resembling steroids for the plants. Cannabis can utilize up to only 0.12 to 0.15% CO2. Roughly, this is about 1200 to 1500 ppm. 

Although CO2 will not help to increase cannabinoids such as THC or make it more potent, it will help in several ways:

• Foliage develops faster
• The plant grows up to 30% faster than usual and also flowers faster
• Foliage will be thicker, including leaves and stems
• Fewer chances of wilting
• The plant becomes stronger with compact or dense growth

How Do You Introduce Additional CO2 in Your Grow Room?

Before delving into this further, it’s important to understand that you’ll have to keep your grow room sealed to prevent wasting CO2. If you can’t keep it sealed permanently, you must at least seal it when you introduce CO2. Sealed rooms are called closed-loop grow rooms. You can also create a setup where you vent some air out frequently to maintain a balance in the grow room. However, as mentioned, seal the tent or grow room when introducing CO2. 

In the image above, you can see a combination of both closed-loop and vented grow rooms. You can choose either of the two methods before planning to use CO2. 

There are multiple ways to introduce more CO2 in your grow room, but most of them don't allow you to control the gas flow rate into your room. So, we will look at the two most effective ways and introduce other alternatives.

Whatever method you choose, you must invest in a high-quality CO2 setup and choose the best components your money can buy. If the CO2 setup's cost is too high, consider holding off on the project for now.

So, let's take a look at the two best methods to introduce additional CO2 in your grow room.

Carbon Dioxide Generators (Propane and Natural Gas)

Resembling a patio heater, CO2 generators are the most popular method of introducing more CO2 in cannabis grow rooms. They are also called CO2 burners. 

These devices burn either propane or natural gas to produce carbon dioxide for your plant. And they come with automatic power switches and valves to control the CO2 flow rate to a specific ppm that suits your grow room. 

Since they use natural gas or propane, you need to find a reliable, high-quality retailer around you to acquire them. 

There are a few things you must consider before choosing CO2 generators, such as the following.

Tackling Excess Heat and Humidity Produced by CO2 Generators

If you have a smaller grow room with only a few cannabis plants, CO2 generators may be overkill. They generate a lot of heat and humidity due to the constant burning, which can be challenging to regular in smaller rooms. 

Typically, most CO2 generators tend to increase temperatures by 5 degrees Fahrenheit and humidity by 7% RH.

You may need to use air conditioners to control the indoor environment with CO2 generators.

Similarly, these devices also produce a lot of humidity. For every gallon of propane burnt, they produce around 0.8 gallons of water, and for around 100 cubic feet (ccf) of natural gas burnt, they produce around 1.1 gallons of water.

This can significantly increase the humidity levels in your grow room. So, you may also need to invest in a ventilation system and dehumidifiers to maintain the humidity levels.

Avoiding Sulfur Leaks in CO2 Generators

Both propane and natural gas contain sulfur (some canisters more than others). In the CO2 generators, this sulfur is converted into sulfur dioxide during the burning process. And if this compound leaks into the air, it binds with moisture to form sulfuric acid.

This sulfuric acid isn't a good compound for your plant. Even a negligible level of it — as little as 0.5 ppm — can cause burn spots on your plant's leaves. Plus, long-term exposure to the same can cause premature leaf drop and flecking on your plants.

So, we recommend buying gas with low sulfur levels to prevent it from leaking and hurting your plant. 

If your device uses propane, use propane gas with an HD 5 Grade. And if you are using natural gas, choose canisters with less than 1 grain of sulfuric acid, i.e., 64.86 per 100 cubic feet.

Adding Air to Balance the Oxygen Levels

Since the CO2 generators burn gas to produce CO2, they require a constant supply of oxygen. Thus, you need to introduce air into the grow room to balance the oxygen levels. Basically, this means you need to pay extra attention to your ventilation setup. 

Most CO2 generators need, on average, a square-inch diameter pipe for every 2,000 Btu/hr (British thermal units per hour) of heater input.

Compressed Liquid CO2

Compressed CO2 is manufactured to be used for small grow rooms, and you can buy it at your local hydroponic stores, home brewing stores, or compressed gas facilities. So, this is the ideal method to introduce more CO2 if you only grow a few plants. 

The benefit of using compressed liquid CO2 is that you can introduce CO2 in a controlled manner into your grow room. All you have to use is emitter devices to control the flow rate. Plus, they don't produce any heat, humidity, or sulfur — unlike CO2 generators — making them ideal for smaller grow rooms.

Compressed CO2 is nothing but liquified CO2. They are also called CO2 tanks and CO2 cylinders. Manufacturers extract CO2 from the atmosphere, compress it until liquefaction, and store them in metal cylinders. 

You can purchase these cylinders in various sizes, and once you are done, you can return them to the seller for a full replacement tank. Most retailers sell these cylinders by the pound (lb), from 20 to 100 lbs. 

One pound of liquified CO2 equals about 8.5 cubic feet of CO2 gas.

And these tanks come with a refrigeration system to maintain the CO2 temperatures at 0 degrees Fahrenheit, so it stays liquid.

When introducing CO2 from these cylinders, you can use a plastic tubing of ¼ to ½ inch with tiny holes spread about a foot apart for ideal gas distribution.

Apart from the cylinders, you also need to buy the following components to complete your compressed CO2 system:

• A pressure regulator to control the tank pressure to around 5 pounds per square inch (psi)
• A flow meter to adjust the CO2 rate of flow 
• Solenoid valve connected to a timer to automatically cut off or open the flow
• Other hardware components like fitting and piping

Other Methods to Introduce More CO2 Into Your Grow Room

Apart from the two methods mentioned above, many growers use other methods to introduce additional CO2, such as the following:

Sodium Bicarbonate and Vinegar

Many growers mix sodium bicarbonate and vinegar and place it in into their grow room. When these two compounds react with each other, they produce CO2.

Since the CO2 produced is in low amounts, this method is best suited for smaller grow rooms.

The problem with these three methods is that they are pretty unreliable. You do not get the control on CO2's flow rate or volume, which means the additional CO2 may be too little even to make a difference for your cannabis plant.

Dry Ice

Using dry ice for more CO2 to increase cannabis yields is perhaps the easiest method of all. You simply have to place a solid block of dry ice (frozen CO2) into your grow room.

The dry ice gradually breaks down and melts, releasing CO2 into the grow room.

Compost

Compost is another simple method to add more CO2 into your grow room. Growers place a bag of compost near their cannabis culture, which slowly releases CO2 into the air.

The benefit of this method is that each bag can last up to three months, but there is no way to switch off or adjust the CO2 flow.

How to Use CO2 to Increase Cannabis Yields?

Typically, our atmosphere contains around 400 to 410 ppm of CO2, enough to grow a regular CO2 plant. On the contrary, if the CO2 levels dip below 200 ppm, the plant halts growth entirely.

However, studies have proved that plants experience continually increased growth until the CO2 ppm reaches 10,000. That doesn't mean you introduce 10,000 ppm of CO2 into your grow room.

Anything above 3,000 ppm is dangerous for you even to breathe in, and CO2 above 5,000 ppm in the air can be lethal for you. 

For optimum cannabis growth, we recommend introducing 1,200 to 2,000 ppm of CO2 into your grow room. Even 1500 ppm will make a difference. This amount of CO2 can make your plants grow up to 30% bigger!

If you want to use such high levels of CO2 in your grow room, you also need to supplement it with high-quality lights. Read on to know more.

Also, with additional CO2, your plant can handle higher temperatures of around 85 to 90 degrees Fahrenheit. 

However, remember to constantly calibrate the climate control and light panels so the temperature and light levels match the CO2 levels. Otherwise, your plant may get damaged due to CO2 overdose.

How Much CO2 Should You Add to Your Grow Room?

It's time for some mathematics!

Typically, you need to add CO2 in proportion to the amount your cannabis plant needs, plus the amount lost due to infiltration (minor leaks into your grow room). Here is how you can calculate the amount of CO2 needed for the best results.

On average, the cannabis plant requires around 0.002 to 0.004 cu-ft/hr per sqft of floor area.

And if you have higher grade lighting systems and large leaf areas, you can add more CO2.

Calculating the Plant Usage Rate

To calculate the exact amount of CO2 needed, you must first calculate the usage rate of your plant. Here's how you can do that.

Let's take a 20 x 20 feet of grow room with a cannabis plant that uses around 0.003 cu-ft/hr per sqft. 

The overall CO2 usage rate can be calculated using this formula:

• grow room area x plant usage rate = overall usage rate
• 20 x 20 x 0.003 = 1.2 cu-ft/hr

Thus, the overall usage rate for a 20 x 20 feet grow room would be 1.2 cu-ft/hr.

Calculating the Infiltration Rate

Next, you need to calculate the infiltration rate, i.e., the amount of CO2 lost due to minor leaks and gaps in your grow room. This depends on your grow room's tightness. 

For that, you must first remember the average air change rate per hour, which is around ½ volume air change/hour for a regular, sealed grow room.

Calculating the Total CO2 Needed

Now, let's calculate the total CO2 needed by your cannabis plant to grow bigger.

Let’s take into consideration a grow room of 20 x 20 x 12 feet for this formula. The equation would be:

• Grow room volume x air change rate/hour x 0.000001 ppm x (desired CO2 ppm - average CO2 ppm) = total CO2 required 
• (20 x 20 x 12) x 0.5 x 0.000001 x (1200 - 410) = 1.896 cu-ft./hr 

So, the amount of CO2 your CO2 system must produce is:

• Overall CO2 usage + plant's CO2 usage
• 1.2 + 1.896 = 3.096 cu-ft/hr

Using CO2 Systems as per the Calculations

You can then calculate how much your CO2 system must produce based on the above calculations.

For a compressed CO2 system with a yield of 8.5 cu-ft/lb, use this formula:

• Total CO2 required ÷ compressed CO2 yield 
• 3.096 ÷ 8.5 = 0.364 cu-ft/hr

For a CO2 generator using propane with a yield of 108 cf/gal, use the following formula:

• Total CO2 required ÷ yield
• 3.096 ÷ 108 = 0.028 gal/hr

For a CO2 generator using natural gas with a yield of 105 cf/ccf, use the following formula:

• Total CO2 required ÷ yield
• 3.096 ÷ 105 = 0.0294 ccf/hr

Use these formulas to calculate the total CO2 your system would need to produce for your grow room.

Measuring the CO2 Levels 

We also recommend investing in a CO2 measurement kit to double-check your CO2 injection in the grow room. For this, you can choose the ones listed here:

• A CO2 test kit that pulls air through a tube and checks the levels against a chart
• Hand-held sampler, a battery-operated blower that pulls air across a CO2 sensor
• CO2 monitor, using a dual-beam absorption technology
• CO2cComputer controller that uses an infrared sensor technology

Injecting CO2 Into Your Grow Room

You also need specific devices to control the rate of CO2 injection into your grow room. For this, you can use any of the given below:

• Constant Rate Injection that uses a timer to regular the flow
• Intermittent Injection that injects CO2 based on the ppm levels calculated by the CO2 monitor or controller
• Computer Control Injection that uses wind speed, temperature, humidity, and light levels to calculate injection rate

Remember to only inject CO2 into your grow room when the lights are switched on as the plant carries out photosynthesis during the dark hours.

Directing the Air for Optimum CO2 Spread 

CO2 is heavier than regular air, so it will sink to the floor as soon as you inject it into the grow room. So, you need to inject CO2 above the plant. 

It would help if you kept the CO2 moving around the room, so it's available to your plant. Stagnant air forms a vapor barrier near the floor as CO2 is heavier, preventing your plant from absorbing all the additional CO2 you add.

For this, use fans like horizontal airflow (HAF) fans, turbulators, or oscillating fans.

Using Adequate Light in Proportion to CO2

The additional CO2 is only helpful if enough light is thrown on the plant. If the light is not enough, the plant will not absorb the extra CO2.

You need a light system that produces at least 900-foot candle equivalent light for a typical grow room with the ideal temperature and humidity levels.

A foot-candle is a measurement of illumination, equivalent to the light produced by one candle at a distance of one foot from the plant, and it is equal to one lumen per square foot. 

Also, we recommend using an air-cooled light system with glass insets to reduce the amount of heat produced by the lights by up to 50%.

Is CO2 Safe to Use in Your Grow Room?

As mentioned earlier, CO2 is bad for your plant in excess amounts. But more importantly, CO2 is dangerous for you. 

Mild exposure to CO2 can lead to dizziness, flushing, headaches, increased blood pressure, muscle cramps, or shortness of breath. And severe exposure can induce confusion, coma, fainting, hyperventilating, panic attack, seizure, etc.

Thus, we recommend you always use CO2 detectors and alarms in your grow room. They can alert you of any harmful leaks that may cause you harm.

Otherwise, using CO2 in a grow room using a high-quality setup is relatively safe. Just remember to maintain your CO2 system regularly to ensure it works properly.

Summary: How to Use Carbon Dioxide to Increase Cannabis Yields?

Additional CO2 is a terrific way to increase cannabis yield as it helps your plant grow more significantly than its typical size. So, if you are an experienced grower and want to take your cannabis culture to the next level, you can never go wrong with adding additional CO2 to your grow room.

Keep the temperature and humidity levels in check, use high-power lighting systems, calculate the right amount of CO2 required for your grow room, and invest in a high-quality CO2 system. The rest would take care of itself.