When To Stop Using CO2 During The Flowering Stage

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Similar to all plant life, CO2 is a vital component to the healthy growth of cannabis plants. Functioning in the same way oxygen is imperative for humans, CO2 is a necessary aspect to the survival of all plant matter, and especially important when looking to produce potent cannabis plants with large yields.

Additionally, not only is CO2 necessary for cannabis growth, but increased quantities over the naturally available levels through the environment can further boost the yield and potency of fully matured plants. Obviously, the levels will need adjusting throughout the growing cycle, as too much CO2 can also have its own list of drawbacks.

Below we’ll break down the importance of Co2 and how the levels should be adjusted throughout the cannabis growing process.

What is CO2 And Why is it Important?

Unlike animals and humans, plants derive their energy from the process of photosynthesis. Converting carbon dioxide, also known as CO2, into energy sources via the green chlorophyll filled leaves, this provides the plant the proper nutrition to flourish.

The ending result is glucose, which will act as the main source of energy throughout the growth cycle for the cannabis (or any other) plant. The conversion of CO2 through photosynthesis is broken down as:

  • 6 CO2 + 6 H2O > C6H12O6 + 6 O2

While the above may seem a little abstract, the main takeaway should be the creation of glucose, represented above as C6H12O6, which provides the plant the energy to grow. In addition, the 6O2 represents the six molecules of oxygen that is created throughout the process of photosynthesis.

Marijuana flower blooming medical cannabis plant

The opposite to humans, who take in oxygen and produce carbon dioxide, this ebb and flow creates a somewhat harmonious relationship between animal and plant life.

Because cannabis plants have the ability to make use of nearly six times the naturally occurring levels of CO2, this allows growers to supplement additional CO2 into their growing environments. Although additional CO2 is beneficial for enhanced growth, there is a fine line before it becomes harmful to your cannabis plants.

How To Supplement CO2

Similar to artificially adding extra light to your grow room, supplementing additional nutrients to the soil, or adjusting humidity or temperature levels, you can also artificially supplement additional CO2 to your cannabis plants. Although there will always be naturally occurring CO2 in any environment, strategically increasing the amount of CO2 to a safe level will aid in maximizing the bud development and overall yield of your plants.

There are a few main methods in increasing the CO2 levels for your cannabis plants:

Compressed CO2 Tanks

The most obvious solution, you can simply pump more CO2 into your growing environment via an external tank. Similar to oxygen tanks, CO2 tanks are compressed and widely available from a number of different sellers inside and outside of the cannabis world.

Flowering marijuana cannabis plant medical

In addition, there are quite a few all in one packages built specifically for cannabis growth. These will include tanks, CO2 readers, and the proper equipment to disperse the CO2.

CO2 Generators

Suitable for larger grow rooms, CO2 generators convert other natural gasses into CO2, which can then be monitored and adjusted depending on your plants needs. The conversion is done similarly to the above mentioned CO2 tanks, resorting to the conversion of gasses such as propane into CO2 instead of directly supplementing it.

Other Methods

In addition to the methods mentioned above, here are a few other methods to increase the CO2 levels in your grow room:

  • CO2 Bags – Acting as an artificial method of recreating photosynthesis, these will increase CO2 levels with access to direct lighting
  • CO2 Bottles – Similar to the above mentioned bags, these are another format of slow releasing CO2 without the need for tanks or generators

How Much CO2 Do Your Plants Need?

Measured in parts per million, or referenced as PPM, CO2 levels will be the key aspect of manipulating the successful growth of your cannabis plants. Once you have determined which method of supplementing CO2 is best for your grow room, monitoring the PPM throughout the growth cycle will make or break the health of your plant during the final stages of flowering.

The natural CO2 levels in our environment are around 400 PPM on average, with increased levels past this amount seeing improved photosynthesis within plants. With nearly a 50% increase in photosynthetic production when levels reach around 700 PPM, it is clear that increased CO2 levels will enhance the growth process.

Growing sativa and indica strains indoor

However, this is not a linear progression above this number, as there will be diminishing returns as the CO2 levels increase past that level.

Be aware, once CO2 levels reach above 3,000 PPM it becomes medically dangerous, reaching near fatal levels above this number for humans. It is recommended to adjust your CO2 levels depending on the power of your lights, as lighting and CO2 levels will directly correlate in terms of photosynthesis.

Below is a loose guideline for lighting and CO2 levels:

  • 1000 Lumens – 500 CO2 PPM
  • 2000 Lumens – 750 CO2 PPM
  • 3000 Lumens – 1000 CO2 PPM
  • 4000 Lumens – 1250 CO2 PPM
  • 5000 Lumens – 1500 CO2 PPM

How Should You Adjust CO2 Levels Throughout the Growth Process?

While the optimal methods for supplementing CO2 are widely debated, there are some rules of thumb when it comes to adjusting your CO2 levels throughout the various stages of growth. Because direct lighting and CO2 go hand in hand during the process of photosynthesis, CO2 supplementation will only be necessary during the times of light exposure.

Vegetative Stage

Because the vegetative stage is fairly intensive when it comes to the majority of your plants fundamental growth, CO2 will play a vital role increasing the speed, size, and health of this portion of the growth cycle. CO2 supplementation can occur throughout the entirety of this stage.

Flowering Stage

Supplementing CO2 for the first two or three weeks during the flowering process becomes one of the more crucial time periods for supplementation, as this can boost the initial stages of flowering. This will not only speed up the process, but also improve flower size.

Growing sativa and indica strains indoor

It is debatable whether CO2 supplementation is beneficial after the 3-4 week time period, so your mileage may vary after this stage.

Pros and Cons of Supplementing Co2


  • Faster and healthier rooting during the vegetative state
  • Increased flowering
  • Larger yields


  • Expensive to implement high end CO2 systems
  • Risk of damaging the plant if exposed to excessive levels of CO2

Final Tips

Supplementing carbon dioxide to your growth cycle is obviously a proven method of improving the overall efficiency and success of your plants growth. Due to the fact it is one of the more expensive enhancements to add into your process, remaining vigilant about monitoring CO2 levels while also experimenting with cycling the CO2 throughout the most intensive growth periods will retain the health of both your plant and wallet.