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Does CO2 speed up flowering?

Tom Starley
December 12, 2023
8 min read
A close up of A CO2 regulator.
A close up of A CO2 regulator.
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In the world of indoor gardening, the quest for perfect growing conditions is a constant endeavour. Carbon dioxide (CO2) plays a pivotal role among the many factors influencing plant growth. This is especially the case in controlled environments like grow rooms or grow tents 

This becomes even more interesting when we delve into plants like cannabis. Cannabis is known for its specific flowering needs. It’s also well known that environmental conditions have a profound effect on the development of cannabis plants. 

So, this leads us to an essential question. Does boosting CO2 levels in indoor settings speed the flowering process of plants, particularly cannabis? 

This post will uncover the science behind CO2's role in plant development. We’ll also cover how manipulating its levels can potentially transform your indoor garden's flowering stage.

Disclaimer: Any information given on this site is for educational purposes only. Please ensure if you’re growing cannabis, you’re doing so in accordance with the law and subject to appropriate permissions and licenses of the applicable country.

What is the role of carbon dioxide in plants?

Carbon dioxide isn't just a component of the air we breathe. It's a cornerstone of plant life, especially when it comes to growing indoors. 

Let's break it down. Plants rely on a process known as photosynthesis. This natural process is how plants convert light, water, and CO2 into the energy they need to grow. 

Indoor environments, unlike outdoor settings, often have limited natural CO2 sources, which can restrict plant growing.

Now, why is CO2 so crucial for indoor plants? In confined spaces such as indoor gardens, air circulation is more controlled. This means that the levels of CO2 can be lower than what plants ideally require. 

For plants to thrive, particularly during the critical flowering stage, an optimal level of CO2 is essential. This is especially true for cannabis. It’s well known to respond positively to increased CO2 levels during its growth cycle. 

If you can understand and manage CO2 levels indoors, you can create a better environment for plants to flourish.

CO2 and flowering: the connection

The journey from a seedling to a flowering plant is fascinating. CO2 plays a significant role in this process, especially in indoor settings. 

When it comes to flowering, plants like cannabis are particularly sensitive to their environment. So, how does CO2 come into play here?

Research indicates that increased CO2 levels can lead to faster growth and flowering times. In the case of cannabis, which is often grown indoors, this can mean a shorter time to harvest. 

This is great for several reasons.

  • Shorter growing cycles mean improved profitability.
  • Less long grow cycles mean less electricity, water, nutrients etc are needed.

Faster flowing times are due to CO2's role in enhancing photosynthesis, the process that drives growth. More CO2 means plants can photosynthesise more efficiently, leading to quicker development and earlier flowering.

This effect of CO2 on flowering isn't just theoretical. Many growers note that their plants flower sooner and more abundantly when exposed to higher levels of CO2. 

This observation is backed by scientific studies, suggesting that elevated CO2 levels can speed up the flowering process. 

However, it's important to note that this is just one piece of the puzzle. Factors like light, water, and nutrients also play crucial roles in any plant's flowering stage.

A women inspects some cannabis plants in an indoor grow room.

Benefits of CO2 enrichment in indoor growing

The advantages of adding CO2 when growing indoors are particularly evident when cultivating flowering plants like cannabis. Here’s why:

Accelerated growth and flowering

Frontiers in Plant Science studies demonstrate higher levels of CO2 can speed up the growth and flowering stages of cannabis. This leads to a shorter overall growth cycle.

Enhanced yield and quality

Research referenced in Cannabis Business Times shows that CO2 enrichment improves plant growth and enhances the yield and quality of cannabis. This contributes to more robust and potent flowers.

Optimised plant health

As indicated in the Nature Sustainability paper, increased CO2 levels contribute to healthier plants by enhancing photosynthesis. This leads to stronger, more resilient plants.

Broader scientific understanding

The article from Oxford Academic helps us understand that CO2's role in plant physiology extends beyond simple growth enhancement. It impacts numerous aspects of a plant's development and flowering stage.

CO2 enrichment in indoor growing (especially for cannabis) offers a multitude of benefits. From quicker grow cycles and improved yields to enhanced overall plant health. Understanding and utilising this method can significantly optimise indoor cultivation practices.

Applying CO2 enrichment indoors

Successfully supplementing CO2 when growing indoors requires understanding and precision. Here are key points to consider:

Setting up the right equipment

Invest in CO2 generators or tanks. You’ll also need a reliable monitoring system to maintain optimal CO2 levels for your plants.

Maintaining optimal CO2 concentration

Aim for a CO2 concentration of around 1500 ppm during the first few weeks of flowering. This is economically viable, doesn't exceed plant-tolerable levels and is a safe level for humans.

Use our CO2 grow room calculator to help you determine the flow rate you’ll need for the size of your grow space. 

Balancing CO2 with other factors

Ensure other environmental conditions like temperature, humidity, and light are also optimised for your plants. Extra CO2 works best under ideal growing conditions. Check out our post about the ideal grow room temperature with CO2 if you need some tips.

Ventilation and safety

Proper ventilation is crucial to prevent CO2 buildup to harmful levels. Regularly monitor CO2 levels and ensure adequate air circulation.

Customising for cannabis

Cannabis plants, in particular, can greatly benefit from CO2 enrichment. Adjust the CO2 levels according to the plant's growth stage for optimal results. 

This post details appropriate CO2 levels for each phase of growth.

By carefully implementing these strategies, you can maximise the benefits of CO2 enrichment, leading to healthier, more productive plants.

A group of C02 tanks linked up to a regulator.

The downsides of CO2 enrichment

While CO2 enrichment offers numerous benefits, it also has downsides to consider.

Cost and complexity

Setting up and maintaining a CO2 enrichment system can be costly. It involves initial investment in equipment and ongoing expenses for CO2 refills and energy costs. However a good sealed grow room supplemented with CO2 will use less electricity and yield more product.  

Health and safety risks

Elevated CO2 levels, if not monitored properly, can pose health risks to people. Ensure your system has adequate safety measures to prevent CO2 buildup to dangerous levels.

Plant stress

Overexposure to CO2 can stress plants. This causes adverse effects on growth and development. Balancing CO2 levels with other environmental factors like light and humidity is important.

Legal considerations

In some regions, there are regulations regarding the use of CO2 enrichment, particularly for cannabis cultivation. Familiarise yourself with local laws to ensure compliance.

By understanding these considerations, you can make an informed decision about integrating CO2 enrichment into your indoor grow.

Case studies and real-life examples

Exploring real-life applications provides valuable insights into the practical aspects of CO2 enrichment when growing indoors:

Success stories in cannabis cultivation 

Numerous growers have reported significant improvements in cannabis yield and quality with CO2 enrichment. The University of Mississippi study, highlighting enhanced yields under elevated CO2 levels, reflects these successes.

Greenhouse implementations

Many commercial greenhouses utilise CO2 enrichment to boost plant growth and productivity. These setups offer a glimpse into effective strategies and the results achievable with proper CO2 management.

Challenges and lessons learned

Alongside successes, it’s important to consider the challenges faced by growers, such as managing CO2 levels and balancing them with other environmental factors. Learning from these experiences helps refine CO2 enrichment practices.

A man inspects some salad plants growing in an indoor grow room.


CO2 enrichment presents a promising avenue for enhancing plant growth and flowering. Especially in indoor environments like those used for cannabis cultivation. 

The evidence from scientific studies and real-life case studies highlights the potential benefits. These include accelerated growth cycles and increased yields and potency. 

However, it's important to consider the associated costs, environmental impacts, and safety concerns. 

The key lies in balancing CO2 enrichment with other vital environmental factors. Understanding CO2's role within the broader context of plant physiology and indoor growing is essential.

We'd love to hear from you! Have you experimented with CO2 enrichment in your grow room? What were your experiences? Share your stories, tips, and questions in the comments below. 


Does CO2 help during flowering?

Yes, CO2 can help during the flowering stage of plants. Elevated levels of CO2 have been shown to enhance photosynthesis, leading to more efficient energy production. 

This can result in faster growth, earlier flowering, and potentially larger yields. Especially in controlled environments like grow rooms. 

For plants like cannabis, increased CO2 can lead to denser flowers and higher-quality buds. 

Balancing CO2 levels with other factors such as light, temperature, and humidity is important to optimise plant growth and flowering.

Does CO2 shorten flowering time?

Yes, CO2 can shorten the flowering time of plants. By enhancing the rate of photosynthesis, elevated levels of CO2 allow plants to grow more efficiently. Plants can also transition to the flowering stage quicker. 

This accelerated growth and metabolic activity can lead to a reduced overall time to maturity, including a shorter flowering period. 

This effect is particularly useful in indoor growing and commercial cultivation where controlling the growth cycle is important, such as with cannabis plants. 

The effectiveness of CO2 in reducing flowering time also depends on other environmental conditions being optimal. 

Is CO2 good for flowering?

Yes. CO2 is beneficial for the flowering stage of plants. It enhances photosynthesis, which is the process plants use to convert light, water, and CO2 into energy. 

This increased efficiency in energy production can lead to more robust growth, earlier and potentially more abundant flowering, and overall better plant health. 

This can be especially advantageous in controlled environments where CO2 levels can be precisely managed. By carefully adjusting CO2 levels during the flowering stage, growers can often achieve better yield and quality of flowers. 

However, it's important to maintain a balanced environment, as other factors like light, temperature, and nutrients also play key roles in optimal plant development.

Does CO2 fatten buds?

Yes, CO2 can contribute to the development of larger, denser buds. By increasing CO2 levels, plants can photosynthesize more efficiently, leading to more vigorous growth. 

This enhanced growth can result in larger buds as the plant has more energy to allocate to bud development. 

Managing CO2 levels is a common technique for indoor growers to improve yield and bud size. 

Remember to balance CO2 with other growth factors like light, nutrients, and water to achieve the best results.

When should I stop using CO2 in flower?

In cannabis cultivation, it's generally advised to discontinue CO2 supplementation in the last two weeks of flowering. 

This allows plants to transition smoothly into the ripening phase, focusing on developing crucial qualities like aroma, flavour, and potency. 

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Tom Starley
December 12, 2023
8 min read

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