When to Stop CO2 During Flowering: The Art of Right Timing

role of CO2 during flowering stage of marijuana

A seemingly ordinary gas, carbon dioxide (CO2) assumes a critical role in the growth of cannabis plants. Proper supplementation is crucial, especially during the flowering stage. This can help improve growth, health, and yield, among others. 


Excessive supplementation can be risky. It can minimize bud density and hurt the overall quality, among other things. Therefore, it’s important that you learn when to stop CO2 during flowering. 

Read on and let’s talk about the ins and outs of maintaining the right CO2 levels for healthier plant growth. 

The Role of CO2 in Growing Marijuana

Using CO2 in the grow room can bring many benefits. This is true not only in the case of cannabis but also with other green plants. 

Enhancing Photosynthesis

CO2 is like fuel for plants. It helps them do something called photosynthesis. This is when plants use sunlight, water, and CO2 to make food. It is when light energy becomes chemical energy. 

During the flowering stage of marijuana plants, this process becomes even more important. 

CO2 is a key ingredient that allows plants to create the energy they need to grow and bloom.

Boosting Growth and Yield

Photo from Deposit Photos 

CO2 isn’t just any fuel—it’s like a supercharger for plants. When there’s more CO2 around, plants can grow bigger and faster. This is especially true for flowering cannabis. 

With enough CO2, these plants can produce more buds, which can become larger and more resinous. It’s like giving your plants a growth spurt that leads to a bigger harvest.

Read Also: Best Cannabis Bud Boosters

Improving Plant Health

Think of CO2 as a plant vitamin. When cannabis plants get enough of it, they become stronger and healthier. 

The right amount of CO2 during flowering helps plants resist diseases and stress. 

This means your cannabis garden is less likely to suffer from problems, and your plants will stand tall and proud, showing off their vibrant buds.

Enhancing Terpene Production

Terpenes are like spices that give cannabis its unique flavors and scents. CO2 plays a role in producing these terpenes. 

During the flowering phase, having the right amount of CO2 can influence the amount and type of terpenes your plants produce. 

This means you have a say in the final taste and aroma of your harvested buds.

When to Stop CO2 Supplementation

Photo from Deposit Photos 

The journey through the best potential to the most potent marijuana seed’s  flowering stage of cultivation is a delicate one, and the role of CO2 in this phase raises a pivotal question: 

Should the steady stream of CO2 be maintained throughout the entirety of the flowering stage? Or is it time to stop once you reach the late flowering stage? 

While CO2 is undoubtedly a growth catalyst, there comes a point where its continuous provision can have unforeseen consequences.

As marijuana plants move deeper into the flowering stage, their metabolic priorities shift. The focus moves from rapid vegetative growth to the intricate art of bud formation. Prolonged CO2 supplementation at this stage can upset this natural balance. 

While it’s tempting to think that more CO2 supplementation means more growth, the reality is more nuanced. Too much CO2, especially during the later stages of flowering, can disrupt the delicate equilibrium of nutrient uptake and utilization. 

The general recommendation is to stop supplementing CO2 during the last two weeks of the plant’s flowering stage. 

By stopping CO2 supplementation before reaching the late flowering stage of cannabis plants, you are allowing them to focus on transitioning to the ripening stage. Further, this will also contribute to the development of essential compounds that affect the quality of the buds. 

What Happens if You Continue CO2 Supplementation

The allure of rapid growth and denser buds can sometimes tempt indoor growers to keep the CO2 levels flowing without pause. However, this approach can lead to unintended consequences that may ultimately compromise the quality of your cannabis harvest.

  • Nutrient Imbalances: Too much CO2 can disrupt plant nutrients, leading to deficiencies despite apparent growth.
  • Terpene Loss: Continued CO2 may reduce aromatic terpene production, affecting flavor and scent.
  • Cannabinoid Changes: Excessive CO2 might alter cannabinoids, impacting the desired effects of the strain.
  • Environmental Impact: Elevated CO2 can disturb humidity, encourage mold growth, and increase energy use.

Best Practices for CO2 Supplementation in a Grow Room

Photo from Deposit Photos 

Using carbon dioxide in cannabis cultivation can increase yield and improve health, but that’s the case only if you do it right. Below, let’s talk about some of the best practices. 

Monitoring and Measurement for Precision

Regularly employ a trustworthy CO2 monitor to keep a close eye on the levels in your grow room. 

Consistent monitoring allows you to ensure that CO2 levels stay within the recommended ranges for optimal growth and avoid nutrient imbalances.

Experts recommend that grow rooms should have 1,000 to 1,500 PPM of CO2 during the flowering stage. 

Investing in a CO2 controller in your grow room can also be a good thing. This will automate adjustments, ensuring that your plants receive the right levels all the time. 

Tailoring to Growth Stages

Adopt a stage-specific approach to CO2 supplementation. Install a CO2 meter so you can easily monitor CO2 levels and make sure it is right for the specific growth stage. 

During the vegetative stage, increase CO2 levels to enhance plant growth. 

As the flowering stage progresses, gradually reduce CO2 supplementation to align with the changing metabolic demands of the plants.

Timing for Maximum Effect

Time your CO2 supplementation during the daylight hours when photosynthesis is most active. 

This strategic approach ensures that the plants can efficiently utilize the provided CO2 to fuel their growth and development.

Transitioning with Care

If you plan to discontinue using CO2 in the grow room, it’s wise to transition slowly. 

Gradually reducing CO2 levels during the late flowering stage prevents abrupt changes that could stress the plants and impact their final yield and quality.

Knowing when to transition is essential. Doing it too early or being too late will negatively impact your cannabis plants. 

Healthy Air Circulation and Ventilation

Ensuring proper air circulation and ventilation is essential for an even distribution of CO2 throughout the grow room. 

This prevents stagnant pockets of CO2 and promotes uniform plant growth and development.

Nonetheless, it’s also crucial to ensure proper sealing of your grow space to keep the CO2 levels in check. Otherwise, it will be more difficult to control the external environment, making it more difficult to achieve the desired results. 


Photo from Grow Weed Easy 

Knowing when to stop CO2 during flowering is critical knowledge for indoor marijuana growers. As noted above, it’s best to stop supplementation in your grow space during the last two weeks of flowering. 

The continued use of CO2 can hurt plant health. It will not only minimize yield but can also harm the overall bud quality. Hence, it can result in marijuana with an inferior appearance, aroma, and flavor. 

Overall, CO2 supplementation is important, but overdoing it has its risks. 

Frequently Asked Questions 

What is the recommended CO2 level during the flowering stage of marijuana? 

Ideally, the CO2 level should be between 1,000 to 1,500 ppm during the plant’s flowering stage. 

Does CO2 help during the plant’s vegetative stage? 

Yes, CO2 helps during the vegging stage of cannabis plants. This can help stimulate healthier growth. 

Is too much CO2 bad? 

CO2 levels higher than 1,500 ppm are bad for marijuana plants. It can lead to nutrient imbalance and terpene loss, among other problems. 

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