CO2 for Cannabis: Why Do Your Plants need CO2 to increase yields?

Indoor Cannabis Plants
March 19, 2021

CO2 cannabis enrichment is a popular method for expert cultivators looking to boost their harvests. This compound is present in the atmosphere by default. If you want to introduce supplements and see increased fertility, you’ll need to approach it with a plan.

Carbon dioxide is a necessary element for photosynthesis, feeding your marijuana plants and letting them grow big and strong. The more there is, the heavier your crops get, right? Technically, yes, but there’s more nuance to this argument.

Are you ready to take your gardening knowledge and techniques one step further? Let’s explore the relationship between CO2 and cannabis and the best ways to enrich your space for increased yields. 

How cannabis uses CO2

This colorless, odorless gas with no taste naturally occurs in the Earth’s atmosphere in small concentrations. Marijuana plants can’t survive without it in any of their various stages of development. 

Mammals breathe oxygen and release carbon dioxide, which the flora uses for subsistence. They take in CO2 through tiny pores called stomata, combining it with light to produce sugar and flourish.

CO2 for cannabis seedlings kickstarts cotyledon and baby leaf development. Light-based nutrition is critical in that period, as their root systems are still too underdeveloped to take in food from the soil. Large green leaves of mature herbs thrive on photosynthesis, too. 

This compound does wonders, but you shouldn’t add more of it at all costs.

Skip this technique during the seedling stage. The little sprouts are too fragile to extreme environments to make supplementation worthwhile.

You’ll mostly focus on the growth-intensive vegetative phase. CO2 for cannabis plants in vegging plays a vital role in enhancing their health, size, and development speed. 

Cannabis plants in vegetative stage

When it comes to flowering, supplementation can kickstart and boost its initial steps. Stop supplementing around three weeks after your crops start producing buds. 

Carefully managed cannabis CO2 enhancement kicks growth up a few notches, but it can be a tricky, pricy process. Ideally, you’ll start only when you’ve gained a clear understanding of your weed garden’s needs and the benefits such systems can provide.

Transpiration, photosynthesis, and respiration

These three processes all play their part in turning your weed seed into a tall plant rich in buds for you to collect when the time comes. 

Some amounts of CO2 for cannabis are necessary for them to happen, and more is sometimes better. ‘Sometimes’ is the keyword here. Let’s examine each mechanism in a bit more depth.


Transpiration is vital for all living things with roots, and weed plants are no different. 

In simple terms, transpiration is the water flow throughout the stem. It starts when the roots absorb it and ends when the foliage releases it as vapor. The flow transports and delivers all the essential nutrients right where they need to be.

Marijuana releases almost 100% of the moisture it takes in, making sufficient cannabis CO2 amounts imperative.

The element affects how much the stomata open and close. Bigger root systems absorb more fluids, and these pores need to open so leaves can let go of the excess. Otherwise, you face stunted development and poor functioning.

Airtight grow room
Airthight grow room


Photosynthesis is a fundamental process for all live greenery. It’s essentially feeding, letting plants produce sugars vital for growth and health maintenance. 

In this case, cannabis CO2 intake combines with the energy your crops receive from the sun or indoor lamps. The mechanism generates glucose and discharges oxygen into the atmosphere.


Respiration means breathing, and it’s a complementary system to photosynthesis that further promotes development. There are two kinds of respiration:

  • Photorespiration, similar to photosynthesis. The leaves take in CO2 and release oxygen.
  • Dark respiration, outside of photosynthesis. Green things need to inhale and exhale when there’s no light involved, too.

As such, respiration tags along for the ride, aiding the production of the sugars we discussed earlier.

Pros and cons of CO2 for cannabis

Your weed plants need carbon dioxide and a light source to generate sugars. Increase both, and they grow taller and bloom into bigger, stickier buds to award you for the effort. 

All aspects need to increase to see a higher net yield. Otherwise, you’ll be wasting precious time and money.

Cannabis CO2 deficiency is rare and only happens in low-air situations. If it does, you see stunted development and sickly-looking crops.

You can get too much of a good thing, too. Overdoing it can cause nutrient deficiencies of other kinds

Growing marijuana is a balancing act already, even more so if you choose to supplement. We’ll dive into the best methods and techniques soon. For now, let’s talk about the pros and cons of supplementing CO2 for cannabis cultivation.


Create high-light situations and don’t provide more CO2 for cannabis than it needs or can use to reap the following benefits:

  • Faster growth
  • Bigger yields
  • Higher temperature support
  • Smell reduction
  • Natural ventilation


Enrichment without thinking things through first can bring more harm than good. The most common pitfalls for growers are:

  • The expensive setup
  • The requirement for strong lights
  • The need to seal the space

Should you use CO2?

Cannabis CO2 supplementation is a niche technique for a good reason. Think about it this way.

  1. On the one hand, it’s a fantastic way to expand your harvest. Heightened conditions make every seed bloom into an admirable marijuana plant in the least possible amount of time.
  2. On the other hand, it can get expensive and complicated. Plus, there are usually other, more pressing matters to attend to and environmental aspects to amend.

CO2 cannabis enrichment works best when you’ve already optimized everything else. Before you introduce a system, ask yourself the following:

  • Is my garden healthy?
  • Are all products I’m using high-quality? 
  • Is the growing medium good? What about the nutrients?
  • Am I facing mold issues?
  • Are there any pests that could be harming my crops?
  • Is my light system conducive to growth?

If everything’s airtight and your budget can accommodate extra changes, it’s time to take things to the next level with a cannabis CO2 system.

How to add CO2 to your cannabis plants?

When considering the best way to add CO2 to your grow tent, multiple options exist. It is however important to note that most methods do not guarantee controlled ppm (parts per million, used to measure CO2 levels in the atmosphere). For this reason, it’s important to invest in a quality CO2 marijuana setup.

You can’t add CO2 to cannabis outdoors. If you have a room, these tools can be of massive assistance. Some are more suited for bigger gardens, while others are more wallet and beginner-friendly. 

CO2 generators

These tools produce carbon dioxide by burning natural gas or propane. They’re easy to use, as they power on and off automatically when your CO2 levels for cannabis reach a certain ppm. 

It’s also easy to acquire the liquid to charge the generator, but an issue arises with heat. Burning could make the situation stifling in a small space. It’s okay for large rooms, but otherwise, you’ll need temperature control equipment.

Compressed CO2 tanks

These are also pretty accessible. A tank lets you manually introduce controlled quantities of CO2 to cannabis without a generator. You won’t struggle with heat-related issues, but some arm strength is a must.

CO2 compressed tank

Bottled CO2

Don’t feel like working with any heavier equipment? Get pre-packaged pressurized bottles of CO2 for cannabis that slowly release the element. You can’t seal it once it goes off, making it a good one-time solution but a pricey permanent option.

bottled co2 for cannabis
Bottled CO2

The truth is, you can’t avoid spending money on your CO2 cannabis solution. If you’re still iffy about the idea, try these alternatives before committing to a longer-term option: 

  • Composting and fermentation. This method can get a bit smelly, but it works well for a few weed plants. Be careful about bugs and mold, though!
  • CO2 bags. These come with fungi growing in organic matter, which naturally produces CO2. The bags aren’t that beginner-friendly or suitable for bigger tents. 
  • Homemade CO2 for cannabis. A baking soda and vinegar mix is another small-scale solution, but it’s the most affordable option on the list. It’ll slightly increase the CO2 levels for cannabis plants.

1) How much CO2 do your cannabis plants need?

When cannabis plants started evolving, the atmosphere featured much more carbon dioxide than we get nowadays. As a result, our green amigos can use high CO2 amounts for photosynthesis – up to 1500 parts per million (ppm). 

Today, we usually see around 400 ppm. Those CO2 levels for cannabis are okay, but they could do with higher concentrations, which would lead to them producing more food. 

For you as a cultivator, this means that you get more flowers by providing extra CO2. Keep these two points in mind:

  1. You don’t want to go over 1500 ppm. It’s pricey, ineffective, and potentially dangerous.
  2. Extra CO2 for cannabis only works if there’s more light to go around. Switch your regular fixtures for something strong and warm. 

Increase the temperature, light, and CO2 for cannabis plants in a balanced manner for the best results. Overdoing it with one while skimping on the others is a net loss. Nothing bad will happen, but it’s a waste of resources. 

The short answer lies in this graph. It outlines the ideal CO2 levels for cannabis in relationship with light.

co2 cannabis chart

If your marijuana plants turn yellow or begin drooping, cut the enhancement and give them some breathing room. 

Indoor weed gardeners should invest in a quality ventilation system to let out the excess oxygen. If the smell isn’t an issue, keeping the windows open does the trick.

Also, those of you using a carbon filter for grow room shouldn’t worry too much. CO2 for cannabis comes in molecules that are too small to get trapped in one.

2) Seal Your Grow Space

To avoid your precious CO2 (that you are trying to maintain at 1200-15 PPM) from leaking out, ensure your grow area is tightly sealed. Regular air only contains CO2 of about 400 PPM. This means that if it’s allowed to mingle with the air in your grow area, it will dilute the CO2 and render your efforts moot.

When sealing your grow tent space, consider the following:

  • Temperature – When supplementing the CO2 content in your cannabis grow room at the highest possible level, ideal temperatures for effectiveness are between 85°F (30°C) – 95°F (35°C). That said, different cannabis plants tolerate heat differently, and you should therefore watch closely for heat stress.
  • Humidity – Maintain the humidity for growing weed in your grow space at below 60-70%. This prevents mold, as well as other problems. If you notice that the humidity in your grow room keeps getting too high, it might be time to invest in a dehumidifier.

It is important to note that a good hood, or reflector, is important when you’re planning on sealing your grow room.

Most growers use reflectors to intensify the light produced by their bulbs, while at the same time, reducing the heat by built-in cooling mechanisms available in most options. Reflectors with air-cooled tubes will ensure that your sealed grow area has the best environment for your cannabis plants in terms of increased light and reduced temperature.

 3) Add CO2 From Above

The concept of CO2 “raining” on your cannabis plants is effective because C02 is heavier than air, and it tends to immediately sink to the bottom. So, for it to effectively get to the leaves, which you are targeting, locate your CO2 cannabis enrichment method above your plants.  

Also, to optimize the increased CO2, and get the best results, a small fan placed on the floor pointing upwards can ensure the CO2 keeps circulating throughout the room and floating above your plants. You’ll get the best results when you make sure CO2 is evenly dispersed over your plants.

When applying your CO2 take measures to ensure that you do not breathe it in. CO2 is dangerous and even lethal to humans in high doses, As such, ensure that your grow space is sealed off from any living space as well.

 4) Turn off CO2 at Night

Unlike animals, plants actually stop “breathing in” at night! Do you know what this means for you? Savings!

Turn off your C02 enhancement system half an hour before you turn off your lights, and turn them on another half hour after you turn on your lights. This means your CO2 will be on-off one hour longer than your lights. Imagine the savings on an hours’ worth of CO2 each day! It has been proven that this adjustment does not affect the benefits of added CO2.

5) Using CO2 in veg

The increase of CO2 is most effective in the vegetative stage. This is because it increases the speed of vegetative growth resulting in bigger plants in a shorter span of time in the weed’s vegetative stage of growth. Cannabis plants which receive supplemented CO2 in the vegetative stage grow stronger, faster, and healthier, and are able to support plenty of flower without support.

And what’s more, it is very easy to apply in this stage. Just keep the CO2 raining, that’s all! CO2 enrichment in veg is absolutely key!

6) Adding CO2 in Flowering Stage

It is agreed by almost all cannabis growers that running CO2 weed in the first 2-3 weeks of flowering is extremely beneficial in increasing both growth, and the production of healthy buds.

As flowering gets fully underway, the popular opinion is that an increase in CO2 in the flowering stage becomes less effective, and indeed there is little evidence to support employing increased CO2 beyond the first few weeks.

When to stop CO2 during flowering stage?

Stopping CO2 anywhere after the first three weeks is ideal. That said, many growers still choose to continue running CO2 up to 2 weeks prior to harvest.

Cannabis CO2 needs in a nutshell

Overall, adding CO2 to cannabis isn’t everybody’s cup of tea. After all, there are other, more straightforward steps to take that pay off in the long run. It’s still a great way to boost yields and help each seed reach its full potential.

If you decide to give it a shot, don’t go full-blown until you’ve checked everything else. Once you do, sit back and enjoy the speedy growth before you.

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