How to Use CO2 to Increase Cannabis Yields

by Nebula Haze


Table of Contents

Introduction: Using CO2 For Growing Cannabis

Start Using CO2 Today!

6 Best Ways to Add CO2 to Your Grow Room


 

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, many people use CO2 in the wrong way and don’t get any of the benefits.

This cannabis grower uses CO2 injection to increase yields.

This cannabis grower uses CO2 injection to increase yields

Cannabis Plants Need CO2, or They Can’t “Eat”

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

CO2 in the air is essential to life on earth

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

Cannabis plants need CO2 to make energy from light via photosynthesis. Without enough CO2 in the air, plants will “starve” and die because they can’t make energy. Luckily, fresh air naturally contains more than enough CO2 to keep plants alive. However, the rate of photosynthesis in plants is limited by the resource that’s in the shortest supply. That means if you don’t have enough CO2 to use all the light available, the plant’s growth will be limited by the amount of CO2 in the air. The well-established principle of plants being limited by their scarcest resource is known as Liebig’s Law of the Minimum.

What does that mean to you as a cannabis grower? With low-powered grow lights (like fluorescent grow lights or small LEDs), your plant can already “digest” all the light at natural CO2 levels.

If your plant doesn’t need more CO2, adding more won’t help much.

But with powerful grow lights (especially HPS and bigger LED grow lights), regular CO2 levels may not be enough, and the lack of enough CO2 will limit photosynthesis. In other words, some of the light goes to waste. In that case, extra CO2 helps plants produce more energy with the same amount of light, resulting in faster growth and bigger buds. As an added bonus, this environment makes plants more resistant to heat, low humidity, and light stress.

The main downsides are that supplementing with CO2 can be expensive and inconvenient. So before you start adding CO2, it’s a good idea to figure out how much (if any) you should provide to get faster growth. That way, you can decide whether it’s worth it in your case.

CO2 supplementation is very effective with HPS grow lights, which produce a ton of heat and light. CO2 helps cannabis use high light levels and also makes plants more heat-resistant.

A sea of cannabis colas - improve growth with CO2!

Due to the same reasons, CO2 supplementation also increases yields with LEC / CMH grow lights.

A room full of big fat buds!

CO2 supplementation can increase yields with LED grow lights, especially with strong LEDs like the HLG Blackbird at temperatures around 85°F (30°C). Grown by cannabichiro.

CO2 supplementation can increase yields with LED grow lights, especially with strong LEDs like the HLG Blackbird at temperatures above 85°F (30°C).

Fun Fact: Instead of lungs or a mouth, 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. Thanks, plants, we love you 🙂

 

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 cannabis plants grow faster and enhance your yields.
  • Plants can stand higher temperatures – A CO2-rich environment makes plants more hardy against heat. Maintaining 1200-1500 PPM of CO2 in the air allows cannabis plants to handle up to 95°F (30°C). For growers with many hot, bright lights, this can make it easier to keep the temperature within a range that cannabis plants can take.
  • Security – CO2 enrichment involves sealing your grow room, which can be beneficial for security because you’re not venting out hot or smelly air. Certain methods of adding CO2, like using a CO2 generator, will also create smells that help cover up the odor of cannabis directly.
  • Extremely effective with HPS grow lights – Adding CO2 works best in a hot environment with powerful grow lights that produce a lot of infrared light. When adding CO2 with HPS, plant growth can increase by up to 20%. Other HIDs like LEC/CMH grow lights also get a big boost from extra CO2. Big LEDs also get an increase of growth, especially in a hot grow space. Small LEDs or fluorescent grow lights (CFLs or T5s) benefit the least from CO2 enrichment and may not see any benefits, as CO2 was not the plant’s limiting factor.

Disadvantages of Adding Extra CO2

  • Not effective with some grow lights – Adding CO2 is ineffective without high light levels. You need either HPS, LEC/CMH, or strong LED grow lights to produce bright enough light for your plant to gain much from extra CO2. Small LEDs and fluorescents like T5s typically aren’t powerful enough to get significant results with CO2.
  • Need heat – CO2 supplementation is much more effective when the temperature is above 85°F (27°C). Plants need heat in order to perform extra photosynthesis. Adding CO2 to a cold grow room won’t have dramatic results. If your grow space is cold, adding heat will likely make plants grow faster than adding CO2.
  • Sealed grow room – Adding just a little CO2 doesn’t require a sealed room, but if you’re trying to maintain high levels of CO2 (like the recommended 1200-1500 PPM) you should seal up grow area to prevent CO2 from leaking out.
  • Cost – It can be expensive to get started if you want to inject a whole lot of CO2 into your grow area. The cheapest ways to add CO2 are not cost-effective in the long run, but they can be a great way to “dip a toe” and try CO2 out. The best CO2 setups are a bit more pricey to start with, though they become more cost-effective once you buy the initial supplies. That being said, big grow operations should consider all their options to increase yields before investing in CO2 because other changes (like dialing in the grow environment) may make a bigger difference and cost less money.

Should you add extra CO2 to your cannabis grow room? Keep reading to find out!

Example of a room full of cannabis colas growing under an HPS grow light

Which cannabis growers should supplement CO2?

The best time to supplement CO2 for your marijuana plants is when:

  • Big grow lights – Grow lights are HPS, LEC/CMH, or powerful LEDs. You should be giving plants more light than they can use naturally.
  • Hot grow space – Temperature is around 85°F (30°C).
  • Sealed grow room – A sealed grow space prevents the CO2 from leaking out. Once the space is sealed, you will probably need to invest in an air conditioner and dehumidifier to control the heat (from the lights) and humidity (from the plants transpiring). Otherwise, they build up as the hot, humid air in the grow space never gets replaced with fresh air.
  • CO2 is the limiting factor – If you’re considering adding CO2, it’s important to make sure CO2 is your current limiting factor. Adding CO2 will not do anything if something else is limiting plant growth. For example, if you’ve got environmental problems like low light levels, cold, high humidity, or lack of air circulation, addressing those problems may help plants more than adding CO2.

Adding CO2 is most effective when you can seal the grow space to prevent CO2 from leaking out. The most common example is a room with all the windows closed and the door shut. You’ll likely also need to set up an AC and strong dehumidifier to control the heat and humidity.

A "sea" of cannabis colas in this commercial grow room under an HPS grow light

How Much CO2 Do I Need?

You’ve decided you want to add CO2 for your cannabis plants, but how much should you add?

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

When plants evolved millions of years ago, CO2 levels in the air were much higher than today. As a result, plants evolved with the ability to use high 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 can still use CO2 levels at up to 1500 PPM, allowing them to produce more energy from the same amount of light. Growers can take advantage of this increased growth by providing extra CO2 when lack of CO2 is the current limiting factor.

For CO2 enrichment to be the most effective, you should maintain levels up to 1500 ppm of CO2 in your grow space with very bright light.

Cannabis 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 bigger returns on yields than adding CO2.

  • If you’re using smaller grow lights with lower light levels, you will need less CO2 (fresh air will likely have plenty for small LEDs, CFLs, or T5s)
  • Plants should be growing fast & healthy – No nutrient problems and no pest problems, if possible. It will also maximize your yields to use plant training. Healthy and vibrant cannabis plants respond best to extra CO2.

Now let’s learn how to use CO2 enrichment right because I’ve seen a lot of misinformation out there. Too many cannabis growers are tricked by fancy marketing and waste money on ineffective CO2 methods. I want to help you set it up correctly 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.

This grower was able to produce wine bottle-sized cannabis buds with CO2 injection plus a 1000W HPS grow light in a 10’x10′ (3m x 3m) grow room.

Today I will share everything I wish I’d known about CO2 when I started growing, so you’ll know exactly how to 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 cannabis 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 (which is dangerous and should never be used) or slowly releasing CO2 from a refillable tank (the only recommended effective method). You then control how much CO2 is released with a compatible CO2 regulator or timer. This lets you automate everything. Don’t worry; we’re going to walk you through everything below.

 

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, LEC/CMH, 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 get as big a growth increase as if you were using stronger lights.

To determine if you have enough light to supplement up to 1200-1500 ppm of CO2, determine how many lumens your bulbs give off. Then find the square footage of your space (length x width). Lumens/square footage should equal 7,500-10,000 (note: LEDs are not typically measured in lumens, so it’s better to look at the wattage).

Examples of setups with enough light for CO2 injection up to 1500 PPM with HPS, LEC, or LED. These amounts consider the amount of electricity used from the wall, not any “equivalent” light calculation. For example, with a “600W equivalent” LED you should look at the true power draw (usually listed in the product details).

These are general guidelines, but they should help give you an idea of what you’re looking for. More light than this likely won’t increase yields, and this may be more light than your plants can stand, especially if they’re a light-sensitive strain. It can be difficult to control heat at these high power levels, and you may need 7-8 feet of height to keep lights far enough from plants.

Max light (CO2 won’t be able to help plants “digest” more light than this):

  • 4′ x 4′ space
  • 6′ x 6′ space
    • 1200-1800W
    • 270,000-360,000 lumens
    • Examples: 2-3 x 600W HPS
  • 8′ x 8′ space
    • 3000-4500W (depends on whether you can control heat)
    • Up to 640,000 lumens
    • Examples: 3-4 x 1000W HPS or 6 x 600W HPS
  • 10′ x 10′ room
    • Up to 5000W (it’s challenging to control heat above this)
    • Up to 750,000 lumens
    • Example: 4-5 x 1000W HPS or 8 x 600W HPS

Note: The 600W size is the most efficient HPS (it uses less electricity and produces less heat per watt than other sizes), so the recommended HPS lights don’t match up watt-for-watt.

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 may not be 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% RH to prevent mold and other problems. I mention this because plants give off water vapor through their leaves, which means controlling humidity low can be difficult in a sealed room. For bigger operations, you will likely need a dehumidifier.

This means you need to eliminate 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 must cool their lights to keep temperatures in the right range. When choosing a reflector for your grow light, you must decide whether you want one that can be cooled via ducting without letting any of that air enter the grow room and bring down your CO2 levels. Your other option is to use an air conditioner to cool the room.

Winged Reflectors (“Bat Wings”)

Batwing reflectors, also known as a “wing” or winged hood, is basically 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. As a bonus, they are the least expensive. However, wings can’t be used with ducting to control heat. If you plan to use ducting, go to the next choice.

With a winged reflector, the heat from the bulbs radiates downward from the bulbs onto your plants, with nothing in between to shield your plants from the heat. That means you must take other steps to control heat (typically a combination of fans and an air conditioner) in a sealed room.

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 from the same bulb vs being 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.

Bat wing reflectors are a great choice for CO2 injection if you are cooling the room (for example, with an air conditioner). A wing reflector can be used with any size HPS.

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

Cool Tubes

When it comes to your grow lights, a “Cool Tube” style hood is an effective reflector when you want to use ducting. Since you’re venting heat from the grow light, you’re less likely to need an air conditioner. 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.

However, you need to keep the air cooling the grow lights separate from the air in the grow room to prevent CO2 loss. 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.

Ducting needs to come in from outside the grow room (for example, through a hole in the wall), connect to all of your lights, and then vent the heat out of the grow room (for example, through a window) with no leaks along the way!

CO2 Sealed Room & Venting Diagram. Ducting needs to come in from outside the grow room (for example, through a hole in the wall), connect to all of your lights, and then vent the heat out of the grow room (for example, through a window) with no leaks along the way!

Cooltubes can keep your plants cooler by trapping air around the grow light and then exhausting it directly out of the grow space. Some cooltubes even come with an extra large reflector, which directs even more light down to your plants.

Only get a Cooltube reflector if you plan to cool your cannabis grow lights via ducting as opposed to an air conditioner.

Cooltube reflectors can be one way to combat heat in the grow room. Only get a Cooltube reflector if you plan to cool your cannabis grow lights via ducting as opposed to an air conditioner.

Air-cooled hoods

Air-cooled hoods have a wider reflector than most Cooltubes and use a piece of glass or plastic to keep hot air contained near the bulb (and away from your plants). These would be used in the same situation as the cool tubes, though these often 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.

An air-cooled hood is best when you are using ducting to control heat in the grow space. They usually reflect more light downward than Cooltubes because their reflectors are typically bigger.

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

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).

Some cannabis growers recommend keeping temperatures 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 may see less 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 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. Compressed CO2 <– Recommended
  2. CO2 Generator <– Dangerous (don’t put one of these in your home!)
  3. Fermentation
  4. CO2 Bag
  5. Compost
  6. Dry ice

CO2 Generators and Compressed CO2 are the most effective ways to add CO2 to your grow area, but since generators are dangerous I only recommend using compressed CO2. The other options are not dangerous, but also not very effective.

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 should still 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.

Avoid breathing CO2-enriched air as much as possible

The nose knows!

4.) 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.

When growing marijuana, turn off CO2 enrichment at night, marijuana plants don't use CO2 after lights out

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

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 tests show this doesn’t seem to 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.

Vegetative Stage 

CO2 is extremely 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.

CO2 Speeds of Vegetative Growth

Flowering Stage

You also get increased growth and bud production by running CO2, with the most dramatic results during the first month of flowering.

After flowering is fully underway, some growers believe that CO2 is less effective, while other growers feel that running CO2 does increase bud production even in the second half of the flowering stage, all the way until 2 weeks before harvest.

 


 

6 Popular Ways to Supplement CO2

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

  1. Compressed CO2 <– Recommended
  2. CO2 Generator <– Dangerous. Don’t use!
  3. Fermentation
  4. CO2 Bag
  5. Compost
  6. Dry ice


 

1.) Compressed CO2 – Highly Recommended!

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, and should be safe if you follow instructions and set everything up properly.

Pros:

  • Simple, effective way to get started
  • Ability to have fine control over PPM in a room using a regulator or controller
  • Relatively automatic once everything is set up

Cons:

 

  • 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

You will need a refillable CO2 tank (usually cheaper in person than online) which you can take to a welding supply store to get filled.

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

You will also need a regulator with a control valve to automatically add CO2 only as needed, and to maintain the desired level.

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

Learn more about getting set up with compressed CO2

 

2.) CO2 Generator – Don’t use! These are DANGEROUS and can kill or seriously injure people.

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. But even the more advanced CO2 generators that have been specifically built for gardening applications produce dangerous and potentially deadly carbon monoxide.

Summary: Never use a CO2 generator because they produce carbon monoxide that can kill or seriously harm you (including brain damage)! Not worth it.

 

3.) Fermentation

Fermentation uses natural processes to produce CO2.

Notes:

  • Produces relatively low levels of CO2 so not particularly effective
  • 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.

 

Notes:

  • 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)

CO2 bags don’t produce a whole lot of CO2

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

 

5.) Compost 

Some growers use the composting process, which produces a small amount of CO2.

 

Notes:

  • Often smelly and unsanitary
  • With home-made compost, it’s very difficult to know if you’re even adding a significant amount 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.

Pros:

  • 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 the temperature of grow room, in fact, dry ice will slightly cool your grow room

Cons:

  • 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 on plants is not an effective way to provide CO2.

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.

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

 

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?

Like nearly all plants, marijuana stops using much 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 its 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 to 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, especially 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 growth factors and eliminated major growing problems to see the biggest benefit from adding CO2.

I’d like to point out that there are many great ways to increase your marijuana yields, such as choosing a high-yielding strain, providing a good warm environment, and using plant training techniques. Mastering these first may be more effective in increasing your yields than adding CO2.

Before you consider CO2, you should also 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 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, 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…

  • 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 problemsbugs, 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 60% RH in my sealed room while running CO2?

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 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?

Tanks or Bottles of Compressed CO2

 

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

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.

You will need a refillable CO2 tank (usually cheaper in person than online) which you can take to a welding supply store to get filled.

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

You will also need a regulator with a control valve to automatically add CO2 only as needed, and to maintain the desired level.

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

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)

 

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!

 

 


 

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