What Role Does CO2 Play In Cannabis Growing?

Last updated: 10 May 2024

co2 for plants

Just like humans can’t live without air, plants need CO2 to survive. CO2, or carbon dioxide, is a colorless, odorless gas that occurs naturally in the atmosphere. Interestingly, even aquatic plants (those that live underwater) need CO2 to perform photosynthesis. Cannabis plants are no different. To ensure that your grow room reaches its maximum potential yield, you’re going to need to utilize CO2. Because it’s easy to control CO2 levels in an indoor garden, this is one clear advantage of growing indoors.

How Is Cannabis Dependent On CO2?

co2 grow room


A cannabis plant’s ability to grow is proportional to the amount of CO2 in its environment. In other words, the more CO2 there is in your garden, the higher your yields will be. Cannabis plants breathe CO2 in through holes under their leaves called stomata. After the plant absorbs CO2, it transfers the molecules to a part of its cell called a chloroplast. These structures then use CO2 for photosynthesis. Using a combination of water, sugar and CO2, the chloroplast creates energy for the plant to grow. Oxygen is a happy byproduct of this chemical reaction – without it, humans couldn’t survive on earth.

What Are The Benefits Of Using CO2?

High CO2 levels in a garden allow a cannabis plant to use light and nutrients more effectively. Cannabis growers measure CO2 in parts per million (PPM), and currently, CO2 makes up about .04 percent of the Earth’s atmosphere – about 410 PPM. However, cannabis plants can thrive with CO2 levels six times this high. Conversely, if the CO2 concentration of your indoor grow isn’t at least at the same natural level as outdoors, cannabis plants will suffer and have difficulty photosynthesizing. Most experienced growers agree that adding CO2 to a garden can increase yields by up to 30%. In addition, a grower who uses CO2 can make their plants complete the growth cycle about 15% faster. CO2 will also help your plants utilize the wattage of the lights in your garden. If you have more than three plants, adding extra wattage without adding CO2 is essentially useless. As a result, adding a CO2 generator to your garden can help your plants use every last watt of light.

The Right Light Is Important!

You’ll need to add extra lights to your grow to properly take advantage of added CO2. However, adding extra lights can have a host of unintended side effects. For example, you can’t just cram your grow full of high-intensity lights like high-pressure sodium (HPS) bulbs. These types of lights put off a ton of radiant heat. As a result, you may need to add some climate controls, like an air conditioner, to your garden.

Another approach to avoid this problem is by using light-emitting diodes (LED) lights. These types of lights have a much lower heat output, but they can still provide your plants with the energy they need.

co2 cannabis

To make sure there’s no risk of overheating and you have just enough light for proper CO2 injection of up to 1500 PPM, follow this simple guide suitable for both LED and HPS lamps:

90cm x 90cm (3ft x 3ft) of grow space – 600W of light

1m x 1m (3.5ft x 3.5ft) of grow space – 2 x 400W of light

1.2m x 1.2m (4ft x 4ft) of grow space – 1000W of light

How Can I Add More CO2?

Now that you know why CO2 is important, you’re probably asking yourself how to add CO2 to your plants. There are several ways that you can do this. Some of them include building homemade CO2 remedies for your plants, while others involve using pre-made kits. There’s no “right way” to do this – each technique has its own benefits and drawbacks.

co2 marijuana

CO2 Generators – What Are They?

For newer growers wondering how to make CO2 for their plants, CO2 generators are a great option. You can find these at your local hydroponic store. These devices create CO2 by burning propane or other fuels. Once the PPM of CO2 in your garden reaches a certain level, the burner will turn off. They’re a great way to add CO2 on a budget, and you can actually build one yourself using a propane or butane stove if you’re a DIY enthusiast. However, they also have some significant drawbacks. First, a generator creates CO2 by burning gas. This, in turn, will create heat. As a result, you may need to add some climate control to your garden. Additionally, generators utilize an open flame to make CO2. If something goes wrong in your garden, your harvest could potentially burn before you get to taste it.

best way of adding co2 to tent grow

Compressed CO2 – Sophisticated But Expensive

Compressed CO2 is an alternative to CO2 generators. They’re similar to SCUBA tanks. Using compressed CO2, a large metal container of compressed air slowly releases the gas into your garden. A device on the tank will measure the PPMs of CO2 in your garden and ensure that it stays at the correct level. You can find compressed CO2 in hydroponic stores, home brewing shops, or even some big-box stores like Walmart. Because compressed CO2 doesn’t involve any open flames, you won’t need to worry about increased heat in your garden. You also won’t need to worry about burning your grow room down. However, there is a trade-off: they’re generally more expensive than CO2 generators.

How Can I Safely And Effectively Add CO2 To My Garden?

At this point, we’ve established that CO2 does increase yield and have gone over a few different delivery systems. Now, let’s look at the best ways to get CO2 where it matters: to your plants. First, you’ll want to make sure that you’re adding the right amount of CO2. Second, you must ensure that your entire grow area is airtight. Third, you need to know when to add CO2 to your garden. Finally, you’ll want to check that your temperature and humidity are optimized.

co2 weed
<1500 PPM

How Much CO2 Should I Add To My Garden?

The best CO2 level for cannabis plant growth isn’t set in stone. Instead, the optimal CO2 for plant growth fluctuates depending on the amount of light and ambient temperature in your garden. However, most experienced growers agree that you shouldn’t use any more than 1500 PPM of CO2 in your garden. Any higher than that and you’ll just be wasting resources. It’s also important to note that CO2 levels higher than 2000 PPM can have negative effects on humans. More than that, PPMs of CO2 higher than 5000 can be fatal. For this reason, commercial cannabis gardens install CO2 detectors that will alert growers whenever the concentration of CO2 becomes dangerous.

No One Wants A Leaky Grow!

Because CO2 is a gas, it’s easy for it to escape from your garden if your grow room isn’t properly sealed. You can avoid this by purchasing a tent from a hydroponic store, which will come in a sealed kit. In addition, you can create your own tent out of panda paper, pipes and duct tape. Regardless of how you decide to build your grow, make sure you release your CO2 from high up in your garden. CO2 is heavier than air, so it will fall toward the ground as it’s released.

co2 generator for plants

Temperature – An Important Consideration

The ambient temperature of your garden can affect how you should use CO2 in your grow room. In general, the higher your temperature, the higher the level of CO2 you should use. Below 70 degrees Fahrenheit (20 Celsius), keep your CO2 level around 800 PPMs. If you run a hotter grow (around 85 degrees Fahrenheit or 30 Celsius), you can pump your CO2 to 1300 PPMs or higher. However, it’s important to note that 85 degrees Fahrenheit (30 Celsius) is extremely high for a cannabis grow. If you’re running your temperature this high, it’s important to keep an eye on your plants to ensure they’re not suffering from heat stress or excess humidity.

when to stop co2 during flowering

Daytime Or Nighttime – When To Run CO2

Plants only use CO2 when they perform photosynthesis. Therefore, you should only run CO2 during daylight hours. While you won’t harm your plants by running CO2 at night, it’s a waste of money. To prevent that, you can attach your CO2 generator or compressed CO2 to a day/night timer. Set the timer to only run during daylight hours. That way, you’ll make sure you’re not wasting any precious resources!

homemade co2 for plants
Light hours throughout the vegetative stage        During the initial 14-21 days of flowering     

When Should I Add CO2 – Flower Or Veg?

CO2 is most important for increasing the rate of the vegetative growth of cannabis – that’s why you want to keep adding CO2 during light hours throughout the vegetative stage, which will indeed help your plants utilize nutrients, light and other resources to speed up growth. As for the use of CO2 during flowering, most growers agree that it’s beneficial for bud production to use it during the initial 14-21 days of flowering. Beyond that, results vary and there’s no proven evidence for improved bud growth, so you might want to decide for yourself. In addition, it’s important to know when to stop using CO2 during flowering. You definitely don’t need to run CO2 from day 1 of flower to the day of harvest.  Even if you keep CO2 on for longer than 3 weeks of flowering, turn it off 2 weeks before the harvest. Keeping it on won’t necessarily hurt your plants, but it’s a waste of resources.

Final Thoughts

Now that you’re familiar with why plants need CO2 after all, you can apply these lessons to your own garden. Figuring out the correct way to use CO2 can be an art form, and it may take a few experiments before you have your CO2 dialed in. However, once you do, you’ll see the benefits almost immediately!

easy-to-grow weedOpen collection
Room size w1.8m l 2.2m h 2.3.Mars hydro fc6500First time grow.Could you use co2 bags with a scrubber ?Sealed environment.10autos in an organic soil.
Hello Simon,There's no right or wrong way to add the CO2, each of them has its own benefits, but do you mean you have a bag with CO2 compressed in it? We would actually advise to use CO2 generators if you're new to the growing hobby
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