co2 ppm for cannabis

How to Use CO2 in Cannabis Grows

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How to use CO2 in cannabis grows is one of the many questions that we’re frequently asked. CO2 is essential for cannabis plants and every other plant, as to them CO2 is like oxygen and they need it to survive. Cannabis plants can deal with CO2 levels of up to 600% the amount that there naturally is in the air around us. Basically, it makes their cells multiply much faster, so if you use extra CO2 during the flowering period you’ll get buds that are much thicker than usual which, if done correctly, makes for a much bigger yield.

If you don’t use CO2 in the right way you could end up with yellowing plants, or long stretched out plants with hardly any buds. You’re going to need to know what you’re doing to implement CO2 correctly. There are many systems that can be used to get more CO2 into your crop; beginner systems that are used as a little extra boost and don’t require much care, and then professional systems that measure the PPM of CO2 that there is in the atmosphere. Professional systems are obviously much more effective and efficient than beginner ones, but they also require more work and attention.

You can use any way of dispensing CO2, connected to a CO2 controller that will shut off the flow of CO2 once it reaches a certain level, and open it again once it gets too low. If all you have is a normal CO2 meter, you can still control the CO2 levels by opening and closing a solenoid valve using a timer. (Solenoid valves are valves that are opened and closed with an electromagnetic charge). Whichever kind of system you use, you must know the exact PPM (parts per million) of CO2 in your grow room.

CO2 needs to be introduced into your room through a silicone tube, with one outlet per plant near the bottom of the trunk. You can also use a 2m tube to go around the grow area with holes facing the center, towards the plants.

Once everything’s installed and ready to go, you’ll need to know exactly how to use CO2. Well, it’s used in the flowering period from the 21 st day onwards, once the buds start to take shape and are slowly popping up at the tips of all of the branches. You’ll need to change your air filtration so that the extractor only works for around 15 minutes an hour because if it’s left on it will get rid of all of the CO2 and all of the effort will have been for nothing. You can use another timer to program the CO2 controller so that it doesn’t turn on when the extractor is on. CO2 should only be administered when the lights are on, as the extraction should be on constantly when the lights are off.

CO2 increases your plants cell walls and multiplies them rapidly, but make sure that you fertilize them also as they’ll end up light and pretty down looking if they get a lot of CO2 but not any nutrition. They’ll also need a slightly higher heat than usual, around 28-32ºC so that the water in the leaves can evaporate slightly faster and the plants can absorb the nutrients straight away. Basically, we want the plants to absorb the nutrients but get rid of the water fast. You’ll need a dehumidifier to lower the ambient humidity to normal levels, because once the temp is raised and your plants begin evaporating water, humidity levels will raise a lot.

Here’s a guide on what you should do and the strength of the CO2 in your grow room from the 21 st day of flowering onwards. EC levels apply if you’re growing in hydro or aeroponics. If you want to measure them in soil you’ll need to measure the water that comes out from the bottom of the flowerpot once you’ve watered; if more is needed you can add it in the next watering, and if it’s too high then the next watering should just be water on its own.

  • Day 21 of flowering: Begin with 800 PPM, and keep it at that when the extractor isn’t on. When watering, you’ll need to raise the EC every time to raise the CO2 levels. For this first week you’ll need about 1.7 EC using normal irrigation water.
  • Day 24 of flowering: Raise the CO2 to 850 PPM, and the EC to 1.8.
  • Day 27 of flowering: CO2 to 900 PPM and EC to 1.9
  • Day 29 of flowering: From this day onwards you’ll need to increase both CO2 and EC every two days. 950 PPM and 2.0 EC.
  • Day 31 of flowering: 1000 PPM and 2.1 EC.
  • Day 33 of flowering: 1050 PPM and 2.2 EC
  • Day 35 of flowering: 1100 PPM and 2.3 EC
  • Day 37 of flowering: 1150 PPM and 2.4 EC
  • Day 39 of flowering: 1200 PPM and 2.5 EC. From this day onwards, increase levels every day.
  • Day 40 of flowering: 1250 PPM and 2.6 EC
  • Day 41 of flowering: 1300 PPM and 2.7 EC
  • Day 42 of flowering: 1350 PPM and 2.8 EC
  • Day 43 of flowering: 1400 PPM and 2.9 EC
  • Day 44 of flowering: 1450 PPM and 3.0 EC (this is the max EC level)
  • Day 45 of flowering: 1500 PPM and 3.0 EC
  • Day 46 of flowering: 1550 PPM and 3.0 EC
  • Day 47 of flowering: 1600 PPM and 3.0 EC
  • Day 48 of flowering: 1650 PPM and 3.0 EC
  • Day 49 of flowering: 1700 PPM and 3.0 EC
  • Day 50 of flowering: 1750 PPM and 3.0 EC
  • Day 51 of flowering: 1800 PPM and 3.0 EC – This is the max CO2 level you can have in your grow room. Continue the rest of the flowering period without raising anything, and make sure to do that root wash 10 days before harvesting.

If you notice your plants get weak or yellowish at any moment, or worse, then stop using CO2 immediately and try and find out what’s going wrong. Either too much CO2 is accumulating or we’re giving them too little and it’s too warm. Make sure you follow the parameters exactly or using it can actually do more harm than good. If done properly, your harvest will be ready a few days earlier and you’ll get a higher yield.

If you have any questions feel free to leave a comment.

Author: Javier Chinesta
Translation: Ciara Murphy

How to Use CO2 in Cannabis Grows; here's a step by step guide on how to correctly use CO2 to get the most out of your plants.

How To Increase Cannabis Yields With CO2

CO2 is commonly found in the air at 400ppm and plants need it as much as they need NPK. Carbon dioxide (CO2) is essential for photosynthesis and when we increase the levels (along with the appropriate environment) it will help our plant grow faster, tougher and produce more buds.

1. How Do Plants Use CO2?

Plants “breathe” CO2 through small holes called stomata, this breathing process along with the appropriate light (light fixture or sunlight) will allow your plant to produce more sugars and oxygen; the sugars being used in plant growth and oxygen the oxygen released back in the air.

Just like all plants, cannabis plants “breathe”, if provided the right way, it can make their cells multiply faster and result in bigger yields. Just make sure that you do it correctly because CO2 can be harmful, resulting in stretched plants with yellow leaves and no buds at all.

An increased amount of CO2 will allow your plant to perform photosynthesis faster, absorbing more light and nutrients, resulting in faster growth and in bigger yield because the buds develop denser.

2. When should you use CO2?

Carbon dioxide can be used in the vegetative and flowering stage but plants only need CO2 when performing photosynthesis so you should only inject it when the lights are turned on.

Also, you shouldn’t increase the CO2 levels always, carbon dioxide should be used in combination with a number of factors, without these elements you may be able to see improvement but won’t be what you expect.

Vegetative stage

When using CO2 during the vegetative stage, your plants will grow faster, stronger and healthier, and when done correctly you will benefit from the bigger yields and in other things like not having to worry with giving support to the branches.

Flowering stage

Some growers say you should only inject carbon dioxide during the first 2-3 weeks of flowering, although others say that an increased CO2 level up to 2 weeks before harvest can result in denser buds, there’s no proof and it’s basically up to you and what you find works in your case.

To properly use CO2, you need to use high-intensity and good quality lights, and according to the type of light you will have to adjust the carbon dioxide levels, temperature and amount of nutrients because cannabis uses CO2 in the presence of light, so the higher the intensity, the more carbon dioxide it will need.

3. Pros and cons of CO2

Despite the benefits, adding CO2 can be expensive. You should think if the benefits are worth it before starting injecting CO2 into your growing space.


  • Faster growth and bigger yields

If you’re an experienced grower and have a top notch growing space, injecting CO2 can help you grow bigger plants that produce better quality and bigger buds.

  • Grow in higher temperatures

Because cannabis plants use CO2 to “ breathe”, a high concentration (1200-1500PPM) of carbon dioxide allows you to have higher temperatures in the growing room, being able to reach up to 30°C.

  • Safety

CO2 can help you mask the smell because some methods of injecting carbon dioxide will create a natural smell that helps cover up the cannabis smell.


  • Not very effective if you don’t have good lights

Most common lights aren’t strong enough to use CO2 appropriately, you will need a very strong LED or Light bulb to benefit from this.

  • Needs an airtight growing space

When trying to maintain an elevated CO2 PPM, you will need an airtight growing space so it doesn’t dissipate.

  • Cost

Depending on the size of your growing room, it can be quite expensive to inject CO2 because the cheapest methods aren’t very good unless you have a small number of plants so you will have to invest a bit.

4. How much CO2 should I use?

Plants are used to high carbon dioxide levels and even though we don’t see it, there is actually CO2 in the air, found at approximately 400PPM.

When injecting CO2 we need to first know our light intensity to then know the limit on how much CO2 our plants can take but have in mind that the maximum is around 1500PPM, the following table gives you an idea of how it should be used.

CO2 and Light intensity

Lumens CO2 (PPM) Temperature (recommended) Nutrients (approximate PPM)
1000 500 20 °C 700
2000 750 20 °C 850
3000 1000 30 °C 1050
4000 1250 30 °C 1300
5000 1500 30°C 1500

If you see your plants getting weak or yellow stop using CO2 and try to find out what’s wrong, when this happens it’s usually too much CO2 accumulated or it’s too hot.

Remember that CO2 doesn’t do magic and increasing the CO2 without the appropriate environment will damage your plants.

When growing indoors it is crucial to have a ventilation system for air exchange, under good lights plants can use CO2 very fast and when the levels fall to around 200PPM the growing rate will be slowed down.

If you don’t want to invest in an exhaust fan or CO2, you can easily increase it by opening your window and letting CO2 in and oxygen out.

5. Recommendations

  • Always make sure you can benefit from CO2, using carbon dioxide inappropriately can damage your plants.
  • To know if you need to inject CO2 read the specifications, most manufacturers will indicate if you need to increase the levels and how much.
  • Have a good CO2 meter in your growing space because if the levels go over 2000PPM it will be toxic for your plants.
  • You can stop injecting CO2 when the lights are off because plants can’t perform photosynthesis without light.

6. How to add CO2 to your grow room

There are several ways to inject carbon dioxide to your growing room, some are more suited for bigger grows than others and can be more expensive but there are ways to increase the CO2 levels in all types of grows.

CO2 generator

Carbon dioxide generators are easy to use and can have an integrated timer that will turn on or off automatically when needed, the downside is they work by burning natural gas or propane and will produce heat so it’s better suited for big growing spaces in which the climate is controlled.

Compressed CO2 tanks

This is the ideal choice for smaller growing spaces, depending on when you live, it can be fairly easy to find CO2 tanks.

CO2 tanks contain saturated carbon dioxide so they don’t produce heat but you will need to buy equipment to automate it if you wish to.

Bottled CO2

Some brands sell bottled CO2 for those who don’t want to deal with expensive or heavy equipment, this easy-to-work with pre-packaged carbon dioxide bottles content pressurized CO2 that will slowly release it into your growing room but because you cannot seal it after, you will have to buy a bottle after every 5-7 days and it can get expensive.

It really doesn’t matter how you do it as long as you do it correctly and with the appropriate equipment, if you do it properly you’ll definitely see a big difference.

7. In conclusion

CO2 is better suited for growers who already maxed out their growing equipment and are looking for alternatives to improve their harvests, if you’re a new grower you indeed can try it but it’s better to invest in good growing equipment before trying carbon dioxide.

If you use CO2 in your grow, please feel free to share your experience, leave a comment below!

Carbon dioxide can really improve the quantity and quality of your harvest if used the right way but you have to use it in a combination with the right elements