Questions about pH

A question of a fellow grower:
I started following the PH levels and wanted to understand the ‘why’ better. I work in soil for starters. In the past, we’ve always had PH at 6.4-6.5 throughout veg and flowering. We used to have long, healthy roots, but after some time it stopped happening and now the roots are not looking too good, maybe even burned?! I’ve read a lot and I feel our area of opportunity is with the PH. (We have adjusted our nutes to half of manufacturer recommendation, so that was a major change). I am 5 weeks into my flower with the new 6.2 PH and 2 weeks into my veg at 6.0-6.2. I just started checking the runoff after each feeding and I noticed the PH levels were at 7.1, 7.2, so I’ll lower my incoming PH to 6.0 for a few feedings and now my last reading ranged 6.3-6.5, which seems like an ideal range. Is this the reason for you putting in a lower PH because it naturally goes up? And I think during flower you raise the PH in weeks 4-6?? Why exactly is that? Because at a higher PH because phosphorus can absorb best??

I have another question. We use a CO2 tank and in all other rounds, we have to change it every 2-3 days and this round, have needed to change it literally every 7 or 8 days. What does this say about my plants?? Why are they not taking in more CO2?? There is nothing wrong with the readings.

Well, thank you in advance for your advice and knowledge!

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What is the ideal soil ph level for growing marijuana?

pH is the level of anion and cation uptake by a plant through its root.
This ensures the proper nutrient uptake. Soil pH is one of the important
factors that must be controlled with in an ideal range to give the best
marijuana crop. The range of ideal pH for cannabis plant cultivation varies
slightly due to the technique being used. For example, if you are using
hydroponic cultivation for marijuana you must ensure that your nutrient
solution has a pH in the range of 5.5 to 6.8. This is the ideal pH range
for hydroponic planting. But if you are cultivating organic cannabis you
must maintain a pH within the range of 6.5 to 7 for the best growth of weed crop.
If pH is maintained within the ideal range, the pot plant will absorb all the
necessary nutrients for its growth. If pH is outside this ideal range, your
crop might suffer from deficiencies.

What is the ideal soil ph level for growing marijuana?

For hydroponic technique, it is essential for you to check pH of water at
least once every week and measure pH after adding any chemical or nutrient
to solution. For organic weed farming, pH must be checked once in one or
two week’s time. We must ensure the pH is in the optimal range as if the
soil or solution becomes alkaline that is above pH 7.5, certain nutrients
like iron, copper and manganese will not be absorbed by cannabis plant and
if the pH becomes acidic that is below pH 6 the nutrients like magnesium and
phosphoric acid will become less soluble. The pH can be checked through soil
test kit. We combine sample of soil with a chemical solution. The result of
mixing these two will give us a specific color that can be compared to a give
chart that has color associated with a pH value. This is an easy and reliable
procedure to judge pH of marijuana crop.

Why is soil ph important?
Soil pH is an extremely important factor to control for marijuana as it affects
the nutrient availability to weed plant thereby affecting growth and quality
of crop. If your soil is solution pH is not optimal for cannabis plant it will
show plant disorders like yellow and shriveled leaves.

How can I determine the ph level of my soil used in growing?
There are various methods of checking pH of the solution or soil. The most
popular pH testing methods for Pot is the use of soil testing kits and
electronic pH meter as both are cheap, easily accessible and easy to use
by any lay man. Another method that can be used is litmus test.




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!

This cannabis grower uses CO2 injection to increase yields

Cannabis Plants “Breathe” CO2 instead of Oxygen

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

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!

As an added bonus, supplementing with CO2 in this way makes your plants more resistant
to heat and light stress!

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.

CO2 Supplementation Works Best With MH/HPS and LED Grow Lights!

A sea of cannabis colas - improve growth with CO2!

Powerful LED grow lights are a great choice to use with CO2 injection

Fun Fact: Instead of lungs, plants use hundreds of tiny pores in the leaves
(known as stomata) to get CO2 out of the air. As a byproduct of photosynthesis,
plants release oxygen back into the air. The photosynthesis process generates
most of the oxygen in our atmosphere. Without plants using CO2 for photosynthesis,
we would have no oxygen to breathe!

Pros and Cons of Using CO2 for Growing Cannabis

Benefits of Adding Extra CO2

Bigger Yields, Faster Growth – If you’ve maxed out the other limiting factors
(especially light), CO2 can make your plants grow up to 20% faster, produce
bigger plants, and enhance your yields.

Higher Temperature is Okay – Maintaining 1200-1500 PPM of CO2 in the grow area
allows growers to keep temperatures much higher than normal, up to 95°F (30°C).
For growers with hot bright lights, this can make it easier to keep temps at a
range their plants will like.

Security – CO2 enrichment can be beneficial for security if you seal your grow
room since you’re not venting out smelly air. Certain methods of adding CO2 like
using a CO2 generator will also create natural smells that help cover up the smell
of cannabis directly.

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?

Maintain 1200-1500 PPM of CO2 in grow room for best results when growing marijuana

Millions of years ago when plants were evolving there were much higher levels of CO2
in the air than there is now. As a result, plants evolved to be able to use higher
amounts of CO2 as part of the photosynthesis process, up to about 1500 PPM (parts per million).

Even though CO2 levels in the air are much lower today at around 400 PPM, plants are
still able to use CO2 levels at the higher concentrations, allowing them to produce
more energy from the same amount of light. Growers can take advantage of this increased
growth by providing extra CO2.

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

CO2 supplementation works best when everything else in the grow space has already
been optimized, and for most growers, a little optimization may result in even
bigger returns on yields than adding CO2!

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

Plants should have fast & healthy growth – No nutrient problems and no pest problems
if possible. It will also maximize your yields by using plant training. Healthy and
vibrant plants respond really well to extra 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

2.Seal Your Grow Space (optional)

3.Add CO2 So It’s “Raining” On Plants From Above

4.Turn off CO2 at Night

5.How to Use CO2 in the Vegetative and Flowering Stage

1.) Use the Right Grow Light for Your Space

In order for Co2 injection to be effective, you should use powerful grow lights
like HPS or LEDA good rule of thumb is you should have 7,500-10,000 lumens per
sq foot in your grow area to get the full benefits of enriching with CO2 when
supplementing with 1200-1500 PPM. You need high-powered grow lights like HPS
bulbs or bigger LEDs for this rule to hold true.

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.

Examples of Setups with Enough Light for CO2 Injection up to 1500 PPM

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

If you’re using smaller lights with lower light levels, you will need less CO2! ?
Learn more about HPS grow lights and LED grow lights

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.

This means that you need to get rid of any possible air leaks when the grow space is closed.

If You Do Want to Seal Your Room, Get the Right Hood/Reflector!

Most growers need to cool their lights to keep temperatures in the right range. When
chosing 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”)

A wing reflector will get the job done, but it isn’t the best type of hood you can
get for your MH/HPS grow lights

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 supplment CO2 in an open room. Bat wing 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 controling 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

Cooltube reflectors can be one way to combat heat in the grow room

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.

With a Cooltube, you can use ducting to bring cool air over your light from outside
the grow space, then vent the hot air out without even touching the air in your grow space.

This means that you need to get rid of any possible air leaks when the grow space is closed.
The only air getting in or out should be the air moving over your grow lights. You will
keep this air segregated from your grow space by using ducting hooked up to the right
type of reflector.

In some cases, instead of an open room with batwings, growers will keep the air blowing
over the lights completely separate

CO2 Sealed Room & Venting Diagram

Cooltubes can keep your plants and grow lights cooler by trapping air and allowing it
to be easily exhausted. They are suitable for CO2 enrichment because they let you
exhaust heat from your grow lights without letting outside air touch your grow space.

Some cooltubes even come with an extra large reflector, which directs even more light
down to your plants.



Air-cooled hoods

An air-cooled hood is one of the best types of reflective hoods for growing cannabis
with MH/HPS grow lights

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

These would be used in the same situation as the cooltubes, though these usually are
more effective at reflecting light downwards.

Many air-cooled hoods (like the one pictured here to the right) have the ability to be
hooked up to ducting on both ends, which allows these hoods to be used for CO2 enrichment.

In other words, after you’ve sealed your grow room away from your lights, 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.

Learn more about the different parts of an HID grow light

Once you get your reflector, use ducting to allow air in and out of the sealed grow
space, with the grow light & hood in the middle to rain light down over your plants.

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

When you’re adding CO2, especially higher amounts, you will get the best results at
higher temperatures.

With CO2 enrichment when growing marijuana, you should keep temperatures much higher
than normal

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

Many growers recommend you keep temps as high as 95°F (35°C) when maintaining CO2
levels around 1200-1500 PPM.

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

No matter what, watch plants closely for signs of heat stress and react accordingly!

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 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.

There are 6 popular ways of adding CO2 to the air of your grow area…

1.CO2 Generator <– Recommended

2.Compressed CO2 <– Recommended


4.CO2 Bag


6.Dry ice

CO2 Generators and Compressed CO2 are the most effective ways to add CO2 to your grow area.
I do not really recommend any of the other methods except as a way to try out CO2 for the
first time without having to make a big investment.

Important: Avoid breathing the CO2!

Concentrated CO2 is bad for humans and can kill when it reaches 1% of the air. Although
you should be using safe amounts of CO2 in your cannabis grow room (which should be more
like 0.15% of the air), you might as well make sure you’re safe. I recommend planning your
setup so you can avoid breathing in the air in your sealed grow space for any length of time.
Keep living areas well-sealed from the grow space.

4.) Turn off CO2 at Night

When growing marijuana, turn off CO2 enrichment at night, marijuana plants don’t use CO2
after lights outPlants 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.

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

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

Learn More About CO2 Regulators & Timers

5.) How to Use CO2 in the Vegetative Stage & Flowering Stage

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.

CO2 Speeds of Vegetative Growth

Vegetative Stage

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

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

After flowering is fully underway, some growers believe that CO2 is less effective, and it’s
true that so far no one has been able to prove that CO2 can 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.

6 Best Ways to Supplement CO2

There are a variety of ways to add CO2, some of which are better than others!

1.CO2 Generator <– Recommended

2.Compressed CO2 <– Recommended


4.CO2 Bag


6.Dry ice

1.) CO2 Generator

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

Highly Recommended!
(as long as you use a CO2 generator with safety features)

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 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.

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).

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.

Learn more about getting set up with a CO2 generator

2.) Compressed CO2

Compressed CO2 usually come in bottles or tanks. Compressed CO2 can be one of the most
controlled ways of injecting CO2 to your grow space.

Highly Recommended!

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

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

Learn more about getting set up with compressed CO2

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

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)

5.) Compost

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
CO2-enriched air.

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.”
– Aquanaut38

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.

Compressed CO2

CO2 Generator

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:

  1. Compressed CO2 (available at local welding supply stores, as well as some hydroponic stores)
  2. Pressure regulator, Flow Meter and Solenoid valve
  3. Either a CO2 PPM monitor / controller or a regulator with timer
  4. 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:

  1. CO2 Generator
  2. Controller to regulate CO2 PPM in room and turn off CO2 injection at night
  3. (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!