cannabis co2

How to Use CO2 to Increase Cannabis Yields

Table of Contents

Introduction: How to Use CO2 For Growing Cannabis

Supplementing your plants with extra CO2 can increase your yields and growth by up to 20%, but what’s the best way for a cannabis grower to use CO2? There’s the right way and the wrong way to use CO2, and unfortunately, a lot of people use CO2 in the wrong way and not getting any of the benefits!

This cannabis grower uses CO2 injection to increase yields!

Cannabis Plants “Breathe” CO2 instead of Oxygen

CO2 is short for “Carbon Dioxide,” an odorless gas that’s in the air you’re breathing right now.

Cannabis plants need CO2 as part of the process of making energy from light via photosynthesis. Without CO2 your plants will “suffocate” and die. That’s part of why it’s so important for your plants to get plenty of fresh air.

For growers using lower-powered grow lights (like CFLs or fluorescents), there’s often more than enough CO2 in regular fresh air for your plants to be able to process all the light they’re being given. If your plant doesn’t need more CO2, it won’t help very much to add more because they’ve already got more CO2 than they can use.

If you’re using CFLs or fluorescent grow lights like T5s, there’s probably already plenty of CO2 in the air for your plants to process all the light they’re being given

But things are different when there’s more light being provided than your cannabis plant can naturally use. In high-light situations, supplying more CO2 can allow your plants use more of that light, which results in increased photosynthesis. By getting your plants to produce more energy from the same amount of light, they’ll reward you with faster growth and bigger yields!


One of the downsides is that supplementing with CO2 can be expensive. So before you start adding CO2, it’s a good idea to figure out how much, if any, you should be providing to get faster growth.


Pros and Cons of Using CO2 for Growing Cannabis

Benefits of Adding Extra CO2


Disadvantages of Adding Extra CO2

  • Not As Effective If You Don’t Have Bright Grow Lights – As far as light intensity is concerned, you probably need either MH/HPS or strong LED grow lights to produce bright enough light for your plant to be able to use the extra CO2. CFLs and T5s probably aren’t bright enough to get great results with CO2.
  • May Need to Seal the Grow Area – Although adding just a little CO2 doesn’t require a sealed room when trying to maintain very high levels of CO2 (like 1200-1500 PPM) you probably need to seal up grow area so it’s airtight in order to prevent CO2 from leaking out.
  • Cost of Adding Extra CO2 – It can be expensive to get started if you want to inject a whole lot of CO2 into your grow area, for example in big grow operations. The cheapest ways to add CO2 are actually not very good at providing a lot of CO2 over time but can be a great way to “dip your feet” and try CO2 out. The best CO2 setups in the long run are a bit more pricey to get started with, though they become a lot cheaper once you’ve got your initial supplies.

How Much CO2 Do I Need?



That means in order for CO2 enrichment to be the most effective, you want to maintain levels up to 1500 ppm of CO2 in your grow space with very bright light.

Plants Can Use Up to 1200-1500 PPM of CO2


  • If you’re using smaller grow lights with lower light levels, you will need less CO2!

Now let’s learn how to use CO2 enrichment right because I’ve seen a lot of misinformation out there, causing many cannabis growers to waste a lot of money on ineffective CO2 methods. I want to help you set it up the right way and enjoy the benefits! After years of research and study by commercial greenhouse growers, we’ve learned exactly what’s needed to get the benefits of extra CO2.

Today I will share everything I wish I’d known about CO2 when I started growing, so you’ll know exactly how you can use CO2 for faster growth and increased marijuana yields. Let’s get started!

Beware! Some people (especially companies selling poor CO2 products) will try to trick you into thinking that CO2 is some magical supplement you add to your grow room to make plants grow better. Unfortunately, this is not the case! There are good ways to add CO2… and there are ineffective ways.

The two most effective CO2 enrichment methods are using a CO2 generator or buying tanked or bottled CO2, combining your enrichment method with a CO2 regulator or timer. This lets you automate everything. Don’t worry, we’re going to walk you through the whole thing.

How to Inject Extra CO2 Into Your Grow Room

1.) Use the Right Grow Light for Your Space


If you’re using less light, you’ll need less CO2 to be effective, though you won’t be getting as much an increase in growth compared to if you were using stronger lights.

To figure out if you have enough light to supplement up to 1200-1500 ppm of CO2, determine out how many lumens your bulbs gives off. Then find the square footage of your space (length x width). Lumens/square footage should equal 7,500-10,000.


  • 3′ x 3′ space – 600W HPS or LED
  • 3.5′ x 3.5′ space – 2 x 400W HPS or LED
  • 4′ x 4′ space – 1000W HPS or LED


2.) Seal Your Grow Space (optional)

Regular air only has about 400 PPM of CO2 so if you don’t seal your grow area, any CO2 you add will slowly leak out. While this isn’t important if you only plan on adding relatively small amounts of CO2, if you want to maintain high levels of CO2 up to 1200-1500 ppm of CO2 in the air, you should seal your grow space in order to prevent yourself from wasting lots of CO2.

You should seal your grow room to keep all the extra CO2 inside if you’re adding a lot of CO2

Some things to keep in mind when sealing your grow space:

  • Temperature – If you’re supplementing at the highest levels, many growers recommend maintaining temperatures between 85°F (30°C) and 95°F (35°C) in your grow space for extra CO2 to be most effective, though it’s important to watch plants closely for signs of heat stress as some plants can handle heat better than others.
  • Humidity – You should keep humidity below 60-70% to prevent mold and other problems. Although most grow rooms don’t have humidity this high, I mention this because keeping humidity low can be difficult if end up creating a sealed room. So for bigger operations, some growers may need to use a dehumidifier.



Most growers need to cool their lights to keep temperatures in the right range. When choosing a reflector for your grow light, it’s important to get one that is able to be cooled via ducting, without letting any of that air get inside the grow room and bring down your CO2 levels.

Winged Reflectors (“Bat Wings”)

If all the air in your grow space is being re-circulated constantly, the CO2 levels start to drop as your plants use it up in the photosynthesis process. In this case, you may want to supplement CO2 in an open room. Batwing reflectors are a common choice, and they’ll let you keep several grow lights in an open room that’s being supplemented with CO2.

A winged hood is basically just a reflector with a socket for your bulb and a plug to connect to your ballast. They are the simplest type of “hood” for HID grow lights and also tend to be the least expensive.

However, wings aren’t good for controlling heat because they do not contain the heat from the bulb (like the next options you’ll see listed here) and they also have no built-in cooling features. With a winged reflector, the heat from the bulbs will basically be radiating downward from the bulbs onto your plants with nothing in between to shield your plants from the heat.

One cool thing about batwings is that since they do not have glass between the bulb and the plants, they can deliver up to 10,000 lumens or more than the same bulb in an enclosed hood because the light doesn’t have to pass through the glass before it reaches your plants. But since they’re hard to cool you may have to keep them further away from your plants, which diminishes that benefit.

Cool Tubes

When it comes to your grow lights, a “Cool Tube” style hood is an effective reflector when a bigger hood reflector won’t work, but you need to keep the air cooling the grow lights separate from the air in the grow room.






Air-cooled hoods

Air-cooled hoods have a piece of glass or plastic which keeps hot air contained near the bulb (and away from your plants).









If the temperature is lower than 85°F (30°C), you won’t see as much benefit from adding CO2.

However, since you must seal your grow room to keep all the CO2 from escaping, it’ll likely be easy to keep temps that high when you’re running your grow lights.

For growers supplementing smaller amounts of CO2, it isn’t recommended that you specifically try to raise the temperature of your grow space, but the CO2 can help protect your plants from heat and light stress.


3.) Add CO2 By “Raining” It On Your Plants From Above

CO2 should “fall” onto plants from above if possible. CO2 is heavier than air and will sink to the bottom of your grow area, so you want your CO2 to float down onto your plants. That means any CO2 enrichment method should be located above your plants.



    CO2 Generator4.) Turn off CO2 at Night

Plants actually stop “breathing in” CO2 at night, so you can turn off your CO2 enrichment system when the lights go out!

Save money by having your CO2 enrichment turn on a half-hour after your lights do, and turn off a half hour before your lights turn off.


This will save you many hour’s worth of CO2 injection each day and tests has proven this will not affect the CO2 effectiveness.


In this section we’ll cover exactly how CO2 affects marijuana growth at different stages of life, and what you can do to maximize your growth and yields.

Vegetative Stage


In the vegetative stage, just keep CO2 going during daylight hours, raining down over your plants. There’s not much else to it!

Flowering Stage

Almost all growers seem to agree that you can get increased growth and bud production by running CO2 during the first 2-3 weeks of flowering.



6 Best Ways to Supplement CO2


1.) CO2 Generator

A CO2 generator burns propane, ethyl alcohol, or natural gas to produce CO2 for your grow space.

Highly Recommended!

  • The smell from combustion can help cover up odors

  • Increases humidity in a sealed grow room
  • Can produce heat
  • In order to burn enough fuel to reach the proper CO2 levels, you sometimes run into adverse side effects, such as producing an unhealthy amount of dangerous carbon monoxide. It’s important to only use safe ways of generating CO2.

Note: The cheaper methods of CO2 generation (like burning denatured alcohol in a small stove) make CO2 hard to regulate and can be very unsafe… Don’t use these methods! Only use a professional CO2 Generator!

Because these methods use an open flame and combustion to produce CO2 in a sealed area, there are many safety and fire concerns with this method. It’s highly recommended that you buy a CO2 generator that has safety features to help prevent fires.

2.) Compressed CO2


Highly Recommended!

  • Simple, effective way to get started
  • Ability to have fine control over PPM in a room using a regulator or controller

  • Tanks can explode if there’s a fire


3.) Fermentation

Fermentation uses natural processes to produce CO2.

  • Produces relatively low levels of CO2
  • Can cause an unpleasant odor during the fermentation process

4.) CO2 Bags



5.) Compost


  • Often smelly and unsanitary
  • With home-made compost, it’s very difficult to know if you’re even adding a significant amount of CO2.
  • The pre-made systems like CO2 Boost are better, but they’re still expensive and don’t produce a whole lot of CO2

6.) Dry ice


  • Does not raise the temperature of grow room, in fact, dry ice will slightly cool your grow room

  • Must manually keep adding dry ice at least once/day

Note: Breathing in the Grow Room Does Not Work!

Humans breathe out CO2 with every breath, and since that CO2 is free, it can be tempting to think you can add extra CO2 to your grow room, all-natural, with no equipment needed.

Unfortunately this likely won’t add enough extra CO2 to make a difference. It’s good to spend time with your plants, in fact, I love hanging out in the grow room, but breathing on your plants probably isn’t going to make them grow any faster.


What Does “PPM” Mean?


When CO2 concentrations get even higher, to 10,000 PPM (1% of air), it becomes poisonous to animals. Humans will suffocate at levels that high. In some cases, greenhouse growers will use this to their advantage by raising the CO2 concentration to 10,000 ppm or more to kill bugs like spider mites (but of course they’re careful to keep humans and animals far away!).

But since you’ll be using much lower concentrations of CO2, it is very unlikely you’ll ever expose yourself to negative effects. It’s still always a good idea to protect yourself by staying out of the grow space as much as you can and otherwise reducing how much you breathe CO2-enriched air.




Cannabis doesn’t use CO2 when there’s no light.

Like nearly all plants, marijuana stops using CO2 during the night (dark period). CO2 is primarily used in the day by the plant as part of photosynthesis (turning light into energy), so if there’s no light, there’s little need for CO2.



It’s common for growers to try to add CO2 to their grow area, without realizing that something else is limiting the growth of their plants.


Max out on almost all other growth factors and eliminated major growing problems to see the biggest benefit from adding CO2.




Yet if you have already perfected the other factors of your grow, then adding the right amount of CO2 has been shown to increase overall vegetative growth by up to 20%. If you’ve maxed out your limiting factors and sealed your grow room, then adding CO2 could be the final piece to take your grow to the next level, providing you with quicker harvests, bigger plants and enhanced yields.

If you’re considering CO2 injection, ask yourself…


If your answer is “Yes” to all those questions, then CO2 enrichment may be a great choice for you and your garden!

Use Only the Best CO2 Sources!

How To Get Started With a CO2 Generator or Compressed CO2

“The yeast or whatever they are methods are pretty pointless. I run at 1500 ppm. I’ve run CO2 for years. I’ve noticed larger yields, more heat tolerant plants, and sooner harvest times. I burn propane but I’ve used tanks for years prior. Highly recommend it.”
– Aquanaut38


Option 1: Tanks or Bottles of Compressed CO2

  • Simple, effective way to get started


The most expensive part about adding CO2 to your grow room with compressed CO2 is the initial investment in parts. After that it’s pretty cheap to refill your CO2 tanks.

Get Started with Compressed CO2


If you have an automatic CO2 PPM monitoring system, it’s simple to maintain the CO2 levels that you want.

If all you have is a compressed CO2 with a regulator and timer, you’ll want to inject the room with CO2 for small periods of time while the lights are on, using your timer. You may have to measure the PPM of CO2 over time and keep adjusting how much CO2 is released until you figure out how to maintain a CO2 PPM between 1200-1500 PPM.





2. Pressure regulator, Flow Meter, and Solenoid valve
4. Connecting tubing, fittings, and adapters (usually comes with your set)


Option 2: CO2 Generator

A CO2 generator burns propane, natural gas, or occasionally denatured alcohol. This creates a chemical reaction that produces CO2 + water vapor.

  • The smell from combustion can help cover up odors



However, more advanced CO2 generators have been specifically built for gardening applications, and these are a much better choice for a gardener as they’re built with many safety features. They may be water-cooled, have an automatic shut-off feature, include a valve to handle municipal gas, an overheating sensor, a tipping sensor, and more.



1. CO2 Generator
3. (Possibly) Dehumidifier


Complete Climate Controllers & Timers

Some CO2 controllers can be integrated with a complete climate controller (often sold for people growing with hydroponics). A climate controller can monitor and adjust your fans, CO2 injection, and other factors so you automatically maintain the right temperature, air movement, humidity, and CO2.





8.5 cu ft.


    A complete climate controller will make your life a lot easier!

    Will CO2 work for your space? How do you get set up? Learn everything you need to know about CO2 injection…

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