PART 3 OF 3
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
Learn more about getting set up with compressed CO2
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
CO2 bags use mycelial mass (fungi) growing on organic matter to produce CO2.
CO2 bags like the “Exhale” system claim to naturally provide CO2 for your grow room
Even in a very small space, growers may need to hang 4-5 or more bags (or more!) 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)
Some growers use the composting process, which produces a small amount of CO2.
Compost methods to enrich CO2 for marijuana include “CO2 Boost”
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
Dry Ice is made of cold, solid CO2. As it warms up, it releases that CO2 into the air.
While this method can be effective in the short term, it can be incredibly expensive and
time-consuming to keep this method going for long.
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 dry ice will slightly cool grow room
Not recommended for long-term use because it 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
Can be very tough to regulate the CO2 levels in the air
Dry ice must be used immediately, so you’ll be constantly going back for more
Note: Breathing in the Grow Room Does Not Work!
You can breathe on marijuana plants to enrich with CO2, though it doesn’t work that great
compared to other methods…
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 be 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.
FAQs, Tips & Background Info to Get the Best Results from CO2 Injection
What Does “PPM” Mean?
When people are talking about how much CO2 is in the air, they generally measure in “PPM” or “parts
per million.” In regular air, the amount of CO2 is approximately 300-400 PPM (about 0.03-0.04%
of our air is CO2). But to get benefits from adding CO2 to your grow room, you need to add enough
extra CO2 to maintain 1200-1500 PPM (0.12-0.15%) of CO2 in the air.
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
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.
Why is CO2 enrichment only effective during the “day” period?
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.
Therefore, flooding your grow area with CO2 during your dark period can be a waste of time
and money. CO2 mainly provides benefits when the lights are on.
Why do you need powerful grow lights for CO2 enrichment to be most effective?
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.
Adding CO2 won’t help anything unless you’ve already maxed out other limiting factors,
such as light intensity. Without big powerful grow lights, most growers aren’t able to
achieve the right light intensity marijuana can naturally use at regular CO2 levels.
Max out on almost all other growing factors and eliminated major growing problems to see
the biggest benefit from adding CO2.
I’d like to point out that there are many free ways to increase your marijuana yields,
such as plant training techniques, and mastering these first may even be more effective
in increasing your yields than adding CO2.
Before you consider CO2, you should eliminate any 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.
Your plants can only grow as much as allowed by the lowest limiting factor, and often
that factor is something else besides CO2.
You want healthy cannabis plants and an optimized grow space before 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, 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.
If you’re considering CO2 injection, ask yourself…
Have I already maxed out the amount of light my cannabis plants can use with my current grow
lights? (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?
If I want to supply CO2 levels up to 1500 PPM, 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?
If your answer is “Yes” to all those questions, than 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.”
So you’re ready to add CO2 to your cannabis grow room? These are the two methods used by
commercial and pro growers who are serious about CO2 injection.
Option 1: Tanks or Bottles of Compressed CO2
Compressed CO2 tanks are one way to supplement CO2 in your marijuana grow room
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
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.
Compressed CO2 tank in a cannabis grow room
Get Started with Compressed CO2
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 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.
The nice CO2 tanks can be hooked up to a meter (a CO2 PPM meter) 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 at many hydroponic or welding stores. These can 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 some special equipment:
- Compressed CO2 (available at local welding supply stores, as well as some hydroponic stores)
- Pressure regulator, Flow Meter and Solenoid valve
- Either a CO2 PPM monitor / controller or a regulator with timer
- Connecting tubing, fittings and adapters (usually comes with your set)
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.
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
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 NOT 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:
- CO2 Generator
- Controller to regulate CO2 PPM in room and turn off CO2 injection at night
- (Possibly) Dehumidifier
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
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.
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!
A complete climate controller will make your life a lot easier!
Complete climate controller - available on Amazon.com!