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Marijuana Yields & CO2

by Nebula Haze

How I Wasted $747.23 on Ineffective CO2 Methods
For My Marijuana Garden

Our newsletter subscribers have recently been writing in with lots of questions about how to increase marijuana yields, and many of you have specifically been asking about how to use CO2 (carbon dioxide) to increase yields.

I want you to know that I've personally wasted a lot of money on ineffective CO2 supplementation methods ($747.23 to be exact) before I understood exactly how CO2 enrichment works.

There are good ways to add CO2... and there are ineffective ways.

Some methods of adding CO2 work great for a small space, but terrible for a larger one, and vice versa.

When I first got started with CO2, I managed to use pretty much all the ineffective ways for my grow space before I found out how to use CO2 the right way.

Today I will share everything I wish I’d known about CO2 when I got started, so that you don’t end up wasting money chasing dreams. 

In this article, you’ll learn exactly how you can use CO2 for faster growth and increased marijuana yields.

What is CO2?

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

CO2 (carbon dioxide) can be used to increase marijuana yields... when you know what to do

While humans and mammals need oxygen to breathe all the time, plants “breathe” in CO2 (though marijuana and most plants only use CO2 during the day, they actually “breathe” out CO2 at night!).

Plants need CO2 to grow, and in certain cases, you can inject extra CO2 into your grow room during the day to increase the speed of plant growth.

When people are talking about how much CO2 is in the air, they generally measure in “PPM” or “parts per million.” The amount of CO2 is approximately 300-400 PPM in regular air (0.03-0.04% of the air is CO2).

How can plants use more CO2 than what’s found naturally in the air?

A long time ago, there was a lot more CO2 in the air than there is now. Some scientists believe that this is why many plants can take advantage of more CO2 than what’s naturally found in the air.

CO2 enrichment is only effective during the “day” period.

Like all plants, marijuana stops using CO2 during the night (dark period). CO2 is primarily used by the plant as part of photosynthesis (turning light into energy).

Therefore, flooding your grow area with CO2 only provides benefits when the lights are on.

How does CO2 affect marijuana growth?

CO2 Speeds of Vegetative Growth

CO2 in Vegetative Stage 

CO2 is most effective at increasing the speed of vegetative growth, so adding extra CO2 is one way to grow bigger plants in less time during marijuana’s vegetative stage of growth.

CO2 in Flowering Stage

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

After flowering is fully underway, many growers believe that CO2 isn’t as effective, and it’s true that CO2 has not been proven to directly improve bud production beyond the first few weeks of the flowering stage.

However, a lot of growers feel from personal experience that running CO2 does increase bud production. Some growers recommend that you keep running CO2 all the way until 2 weeks before harvest.

Benefits of Adding Extra CO2

  • If you’ve maxed out the other limiting factors (especially light), CO2 can make your plants grow faster, produce bigger plants, and enhance your yields.

  • Maintaining 1200-1500 PPM of CO2 in the grow area allows growers to keep temperatures much higher than normal

  • It can be beneficial for security since you’re not venting out hot, potentially smelly air (you must seal off the grow area for CO2 supplementation to be effective)

Disadvantages of Adding Extra CO2

  • As far as light intensity is concerned, plants must be receiving about 7500-10000 lumens of light per sq foot for CO2 enrichment to be effective

  • Adding extra CO2 won’t help if your plants are already suffering from nutrient deficiencies or other plant problems

  • In order to keep CO2 near the plants, you must seal up grow area so it’s airtight, which can make it harder to manage temperature and humidity

  • Can be expensive to inject enough CO2 into your grow area to be effective

  • You must keep temperatures between 85°F (30°C) and 95°F (35°C) in order for CO2 enrichment to be effective

  • Every time you check on your plants, you’ll be letting out all the CO2

  • CO2 is bad for you at high levels, so you need to take precautions to

How Can I Add More CO2 To My Grow Room?

There are 7 popular ways of adding CO2 to the air of your grow area...

  1. CO2 Generator
  2. Compressed CO2
  3. Dry ice
  4. Fermentation
  5. CO2 Bag
  6. Compost
  7. Breathing in Grow Area

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

Learn more about whether CO2 Enrichment Is Right For Your Garden...

Some Considerations When Deciding If CO2 Is Right For You...

You must maintain 1200-1500 PPM of CO2 in the air of your grow area for CO2 enrichment to be most effective.

Maintain 1200-1500 PPM of CO2 in grow room for best results when growing marijuanaGrowers seem to agree that optimal CO2 is 1200-1500 PPM in your grow room. If there’s less CO2 than that (especially under 1000 PPM), you won’t get good results with CO2 supplementation. When the CO2 drops under 300 PPM, plant growth will slow down or even stop completely.

If you have a very small grow space (like the inside of a cupboard), then you may be able to maintain 1200-1500 PPM of CO2 in the area with one of the cheaper methods of CO2 enrichment (dry ice, fermentation, CO2 bags, or even breathing).

If you’ve got a larger grow space (such as a closet, a grow tent, or a room) it will be hard to maintain enough CO2 in the air without investing in one of the more expensive options like a CO2 generator or compressed CO2. Scroll down to the “Check It Out” section below to learn exactly what you need.

You must maintain very high temperatures, between 85°F (30°C) and 95°F (35°C).

With CO2 enrichment when growing marijuana, you should keep temperatures much higher than normalWhen you’re adding CO2, you will get the best results at higher temperatures. 

Normally you want your garden to be a comfortable room temperature, but when adding CO2, you want to keep temps above 85°F (30°C).

Many growers recommend you keep temps as high as 95°F (35°C).

If the temperature is lower than 85°F (30°C), you won’t see 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.

Which brings me to the next point...

You must seal your grow room to keep all the extra CO2 inside.

If you don’t enrich the area with CO2 and have bad ventilation in your grow area, all the CO2 will very quickly get used up by the plants and plants will stop growing and eventually die.

Yet if you add extra CO2, it’s like adding more “fresh air” that your plants can use, only at higher levels than what is naturally found in the air.

So, if you want to add extra CO2 at levels above what’s found in the air, you need to seal up your grow area. If you can’t seal your grow area so it’s airtight, then any CO2 you are adding will leak out and CO2 will return to normal levels. For the best results, you want the entire grow area to be sealed so the CO2 stays near your plants.

Luckily, with CO2 you must keep the temperature much hotter than normal, which helps you deal with the heat from lights in a sealed area without ventilation. However, if your sealed grow area still gets too hot from your lights, one option is to seal your hood and hook it up to the exhaust. In other words, after you’ve sealed your light, you can set up an intake and exhaust fan to blow air cool over the lights and have an exhaust fan vent out the hot air without also venting out all your CO2. Another option is to invest in an air conditioner.

CO2 should “fall” onto plants.

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

You’ll get the best results when you make sure CO2 is evenly dispersed over your plants. A small fan on the floor pointed upwards can help keep the CO2 circulating through the room and floating over your plants.

Avoid breathing the CO2

CO2 is bad for humans at the levels you want to achieve for your plants. Therefore it’s important to plan your setup so you can avoid breathing in the air from your grow room for any length of time.

You can save money by turning off CO2 enrichment at night.

When growing marijuana, turn off CO2 enrichment at night, marijuana plants don't use CO2 after lights outBecause plants actually stop breathing in CO2 and start giving off CO2 at night, you should make sure that your CO2 enrichment system is turned off when the lights go out!

In fact, you can 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.

In other words, have your CO2 off for about an hour longer than your dark period. 

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

You must have already maxed out on your grow lights (light intensity) for CO2 enrichment to be effective.

Adding CO2 won’t help anything unless you’ve already maxed out other limiting factors, such as light intensity. Without big powerful lights, like an 1000W HID or a few 600W HIDs, most growers aren’t able to max out the light intensity marijuana can naturally use at regular CO2 levels.

A good rule of thumb is you should have at least 7500-10000 lumens per sq foot in your grow area to get the full benefits of enriching with CO2.

You need to have maxed out on almost all other growing factors and eliminate major growing problems in order to see the biggest benefit from adding CO2.

I’d like to point out that there are many cheap/free ways to increase your marijuana yields, and many of these are going to be more effective in increasing your yields than adding CO2.

Before you consider CO2, you must have eliminated plant problems from your grow. I’d say that the number one way to increase your yields is to prevent plant problems. If you’re suffering from plant problems like too much nitrogen or nutrient deficiencies, you should start here when considering how to increase yields, since these will negatively affect your yields much more than any benefit you get from CO2.

If you’ve already mastered the basics of growing and have healthy plants in your garden, then training your plants properly in the vegetative stage and choosing the best grow lights you can afford are the next steps you should take to majorly improve your yields.

Mastering these factors will often be more effective for increasing your yields than adding CO2.

Your plants can only grow as much as allowed by the lowest limiting factor, and usually that factor is something else besides CO2.

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

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, than 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.


When Should I Use CO2?

If you’re considering CO2, ask yourself...

  • Have I maxed out on the amount of light my plants are able to use? (at least 7500-10000 lumens per sq foot, usually only possible with a 600W or 1000W HID light, or a few 400W HID lights close together)

  • Have I already eliminated all problems from my grow such as nutrient problems, bugs, etc?

  • Have I already mastered (easy and free) growth control methods to increase my  yields?

  • Am I willing to seal up my grow area so it’s airtight?

  • Can I maintain temperatures between 85°F (30°C) and 95°F (35°C) in my grow area?

  • Can I keep humidity below 70% in vegetative and 60% in flowering in my sealed room while running CO2? (Remember, if you use a CO2 generator, it will increase the humidity of the air dramatically so you may need to get a dehumidifier)

If your answer is “Yes” to all those questions, than CO2 enrichment may be right for you and your garden.

Supplementing CO2 is a great choice for those who have maxed out their other options and are willing to spend the money to do CO2 right. For these growers, supplementing with CO2 can increase the number of crops grown per year and allow them to grow bigger plants. If you’ve got a big grow operation, the bigger yields you get each year will pay for the CO2 investment many times over in the long run.

Unless you’ve got a very tiny grow area, the most effective CO2 enrichment method is to either invest in a CO2 generator or to buy tanked or bottled CO2, and then combine your enrichment method with a CO2 regulator.

But you don’t need to figure this all out on your own! Scroll down to our “Check It Out” section to be guided through the process of buying the right CO2 method for your grow.

Now you don’t have to waste $747.23 on ineffective CO2 methods like I did. You are armed with the information to pick the right CO2 enrichment method for your space.

And now, learn about the different ways to supplement CO2...

1. CO2 Generator (burns propane, ethyl alcohol or natural gas)
CO2 generator actually makes CO2 by burning natural gas or propane

  • Many of these can be hooked up to a monitor for no-worries, automatic CO2 enrichment

  • Generates CO2 by burning propane, denatured alcohol, or natural gas

  • The smell from combustion can help cover up odors


A monitor will help you regulate the CO2 PPM levels from a CO2 generator in your grow room

  • Increases humidity in a sealed grow room

  • Can produce a bit of heat

  • Output can be hard to regulate and very unsafe when using the cheaper methods of CO2 generation (like burning denatured alcohol in a small stove)

  • Because this method uses and open flame and combustion to produce CO2 in a sealed area, there are many safety and fire concerns with this method unless you buy a CO2 generator that has safety features to help prevent a fire

  • 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 dangerous to store your bottled fuels indoors (some people are able to use their municipal natural gas, and don’t need to store fuel, which makes this point moot for them).

2. Compressed CO2 (bottled CO2 or CO2 tanks)

Compressed CO2 tanks are one way to supplement CO2 in your marijuana grow room Pros:

  • Simple, effective way to get started

  • Ability to have fine control over PPM in room using a regulator or controller

  • Can be automated with a controller, so relatively automatic once everything is set up


If you get compressed CO2, you'll need a CO2 regulator & valve

  • The equipment you need to get started is expensive, this is one of the most expensive ways to get started with enriching CO2

  • You must lug tanks of CO2 to and from your grow area, which is a possible security concern depending on your grow area and where you get your CO2

  • Tanks can explode if there’s a fire

  • You can enrich the air with CO2 beyond what’s safe for plants or people, so you must use great care to keep the PPM in the right range, and to avoid breathing air in your sealed grow area.

  • In some places, you may need a permit or license to get tanked or bottled CO2 

Note: It’s usually cheaper to get tanked CO2 from a welding supply store as opposed to a hydroponics store

3. Dry ice


  • Very small cost to get started, since dry ice is relatively cheap and easy to obtain

  • The biggest safety hazard is burning your skin from touching the dry ice without protection

  • Does not raise temperature of grow room, in fact will slightly cool grow room


  • Can be a huge pain and expense in the long run since dry ice doesn’t last long

  • Must manually keep adding dry ice at least once/day, which can be tough considering you need to keep an airtight seal in your grow room

  • Can be very tough to regulate the CO2 levels in the air

  • Dry ice must be used almost immediately, so you’ll be constantly going back for me

4. Fermentation


  • Cheap and easy to get started

  • Safe (no dangerous components)


  • Can be hard to produce enough CO2 to be effective

  • You can’t easily regulate the CO2 PPM levels

  • Can cause an unpleasant odor during the fermentation process

  • Impossible to automate, you will need to manually check CO2 levels, and take steps on a regular basisto keep the fermentation process going

5. CO2 Bags
CO2 bags like the "Exhale" system claim to naturally provide CO2 for your grow room

  • Very Cheap

  • Uses mycelial mass (fungi) growing on organic matter to produce CO2, so this method is all-natural and doesn’t have dangerous components

  • Can be effective for a very small grow space


  • Hard to produce enough CO2 to be effective, some growers need to hang 3-4 or more bags over their plants in order to achieve the right PPM in their grow area,

  • Some growers have trouble getting the fungus to grow properly (although you’re not supposed to need to do anything for these bags to work)

  • Tough to regulate the CO2 PPM in your grow area and keep CO2 at optimal levels

6. Compost
Compost methods to enrich CO2 for marijuana include "CO2 Boost"


  • Can be cheap to get started if you do it yourself


  • Often smelly and unsanitary

  • With home-made compost, it's difficult to produce enough CO2 to acheive 1200-1500 PPM

  • The pre-made systems like CO2 Boost are expensive and still don't produce enough CO2


6. Breathing in Grow Room 


  • Free since humans breathe in oxygen and breath out CO2

  • No equipment needed

You can breathe on marijuana plants to enrich with CO2, though it doesn't work that great compared to other methods...

  • Must spend a significant amount of time in the sealed grow area

  • Hard to exit the grow area without letting out all the CO2

  • It’s not healthy or safe for a human to spend time in an area with CO2 levels that are high enough to enrich plants


Check it Out!

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

So you’re ready to add CO2 to your grow room?

Option 1: Tanks or Bottles of Compressed CO2

Compressed CO2 usually comes in metal containers that are under high pressure. It’s often cheaper to buy compressed CO2 from a welding supply store as opposed to a gardening or hydroponic store.

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. You need a tank, valve, timer and ppm meter. While it is expensive to get everything up front, a single tank of compressed CO2 could last several grows by itself, and refills are cheap when you find the right place.

If all you have is a compressed CO2 with a regulator and timer (no automatic CO2 PPM monitoring system), you'll want to inject the room with CO2 for small periods of time while the lights are on. 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

The nice CO2 tanks can be hooked up to a meter (a CO2 PPM monitor) that measures how much CO2 is in the air and adjusts your CO2 output as needed.

For plant growth, you want your CO2 to be between 1200-1500 PPM. The meter is attached to your CO2 tank, and it will start injecting more CO2 into the air above your plants when CO2 levels drop below the optimum. This effectively automates the whole system.

Bottled CO2 can be purchased online, at most hydroponic or at welding stores. These come with a regulator/flow meter which you will need to adjust in order to output the correct amount of CO2.

To use this method of enriching CO2, you will need the following equipment:

1. Compressed CO2
2. Pressure regulator, Flow Meter and Solenoid valve
3. Either a CO2 PPM monitor / controller or a regulator with timer
4. Any Connecting tubing, fittings and adapters

Watch a Youtube video showing the right way to use compressed CO2:

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 cheaper methods of producing CO2 this way (such as a bunsen burner) use an open flame, which is a terrible fire hazard, especially considering you are keeping temperatures above 85°F (30°C) when flooding your grow area with extra CO2.

Because of the hot temperature and the electrical equipment and water that are already in your grow area, I highly recommend against adding a cheap CO2 burner into your grow room and risking a fire.

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.

Please note: As you’re burning propane or natural gas to get CO2, this chemical reaction also adds water vapor into the air and increases your humidity. The increase in humidity is even greater when you generate a lot of CO2 or have a very small grow area. This extra humidity can become problematic in some cases, especially since you must seal your grow area to keep the CO2 inside. If you’re not carefully monitoring the humidity, you may put your plants at increased risk for mold (remember, humidity should always be below 70% in vegetative, and below 60% in flowering). A strong dehumidifier may be what you’re looking for in this scenario.

To use this method of enriching CO2, you will need the following equipment:

1. CO2 Generator
2. Controller to regulate CO2 PPM in room and turn off CO2 injection at night
3. (Possibly) Dehumidifier
4. (Possibly) Air conditioner

Keep in mind: How will you find propane or natural gas on a regular basis? Some homes get municipal natural gas, and this can sometimes be hooked up directly to a CO2 generator

(Optional) Complete Climate Controller

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

If you’re not going to get a CO2 controller and need to use a timer...

If you’re not going to use a controller (which is what you want to do if you can afford it,) you will need to calculate how much CO2 to add to your grow area and use a timer to control how much CO2 gets added.

To calculate the amount of CO2 needed to enrich the air of a room to 1200-1500 ppm of CO2, this is what you do:

  1. Calculate the volume of the growing area by multiplying width x length x height.

    Example: If you had a closet that was 5 ft x 4 ft, and the ceiling is 8 feet high, you would multiple 5 x 4 x 8 = 160 cubic feet of space in your grow area.


  2. Determine the CO2 needed to enrich room to 1200 or 1500 ppm by multiplying the volume of space by 0.0012 or 0.0015 respectively.

    Example: So to get 1200 PPM of CO2 in my 160 cubic feet closet, I’d multiple  160 x .0012 = 0.768 Thus, 0.192 cubic feet (or you can round up to 0.2 cu ft) of CO2 will be needed to bring the CO2 in this room up to 1200 ppm. When you’re buying tanks, 1 lb of CO2 is equivalent to ~8.5 cu ft.


  3.  If you have a sealed room, then you will need to keep adding CO2 based on how much your plants are using. If the room is not sealed, you will need to replace CO2 at a rate equal to the amount plants use plus what’s being vented out. It’s recommended that you regularly test and monitor that CO2 levels are staying where you want them to be.

Because this is tough for most growers to calculate accurately, it’s highly recommended you get a controller that measures and regulates the amount of CO2, and adjust the CO2 injection based on the current readings.