What Are CO2 Bags?

CO2 bags are a simple and cost-effective method for increasing carbon dioxide (CO2) levels in indoor grow spaces, particularly for small-scale growers or hobbyists. These bags contain a mix of natural ingredients, such as fungi, organic matter, or microorganisms, which release CO2 into a space. That’s it. They are just bags or bottles filled with something that produces CO2. 

When it comes to CO2 Bags, and CO2 products generally, there are a few different products on the market. The most popular brand in the CO2 bag space are Exhale bags, but there are other options that are just as effective.

Here we will look at the main types of CO2 products for hobby home growers and small-scale cannabis cultivation set ups.

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What Is Inside A CO2 Bag?

CO2 Bags are usually filled with a combination of organic matter and microorganisms. The organic matter is the substrate. This provides a food source for the microorganisms to consume during the respiration process, producing CO2 through metabolic activity.

Depending on the type of CO2 product, the substrate could be wood based material or some sort of sugar solution. It just needs to be tailored to the biological part. We know from our research that the Exhale bags use mycelium from Turkey Tail mushrooms and they need a woody substrate with plenty of moisture. 

There are also CO2 Bags on the market that do not have a biological component, for example Smart CO2 bags use calcium carbonate which reacts with moisture in the air to produce CO2 (amongst other things).

How Do CO2 Bags Work?

CO2 bags usually contain a mix of some organic matter that acts as a food source for natural biological organisms, such as fungi or bacteria. These fungi or bacteria consume the organic material and respire to produce carbon dioxide as a result. This is much like humans breathing. In very simple terms CO2 bags breathe in oxygen and breathe out CO2. 

Here’s a slightly more in-depth explanation of how CO2 Bags produce carbon dioxide:

Most CO2 bags are filled with a combination of organic matter and microorganisms. The organic matter may be referred to as the substrate, which basically provides a food source for the microorganisms to consume and respire in the process. 

These microorganisms naturally produce CO2 through their metabolic activity. As the microorganisms in the bag grow, respire, and decompose the substrate, they release CO2. This process can gradually increase the CO2 concentration in the grow space, making more CO2 available to the plants.

How To Use CO2 Bags?

There is some debate about how best to use CO2 bags in your grow space. Most people tend to make sure it is above the plants because CO2 is heavier than air and will sink to the lower areas. However, CO2 would be very well distributed regardless of where the CO2 bag is placed because there is usually a lot of air mixing in grow spaces.

The plants in your grow space absorb the increased CO2 levels through tiny pores on their leaves called stomata. This additional CO2 can enhance the rate of photosynthesis, potentially leading to faster growth and increased yields.

How Long Do CO2 Bags Last?

CO2 bags have a limited lifespan, usually around a few months, depending on the specific product and environmental conditions. The bag will stop producing CO2 once these organisms have consumed or decomposed the substrate. People experience a steady decline in the CO2 output over time.

That being said, we know that some CO2 Bags can last well over 6 months, or even longer. They will just produce slightly less CO2 as the months go on.


How Do CO2 Bags Affect Cannabis Plants?

All plants – including cannabis plants – photosynthesise to fuel growth. Photosynthesis is basically the process by which plants convert carbon dioxide (CO2), water, and sunlight into glucose and oxygen. 

In most controlled environments and greenhouse growing spaces, plants are given optimal growing conditions in terms of temperatures, light intensity, as well as water and nutrient availability. When plants are given such great biotic and abiotic conditions it is usually CO2 that becomes a limiting factor for plant growth

Below is a brief overview of how plants use carbon dioxide for photosynthesis:

Light Absorption

Chlorophyl in the plant chloroplasts needs to absorb light for photosynthesis to take place. The wavelengths of light that plants use to drive photosynthesis are between 400nm-700nm. This is Photosynthetically Active Radiation (PAR). There are also accessory photopigments like carotenoids which can extend the wavelength range used for photosynthetic activity, as well as photoprotective pigments like anthocyanins which protect photosynthetic apparatus from light damage (e.g. UV-B: 280-320nm).  

Note: Red and Blue wavelengths are generally considered to be most relevant for photosynthesis. Other wavelengths are also relevant to photosynthesis, as well as plant photomorphogenesis, phototropism and photoperiodism.

Conversion of CO2 and water

During the light-dependent reactions, the absorbed PAR energy is used to split water molecules into oxygen and hydrogen. This process produces energy-rich molecules like ATP (adenosine triphosphate – also used by human cells) and NADPH (nicotinamide adenine dinucleotide phosphate). The oxygen produced is released into the atmosphere, while ATP and NADPH are used in the Calvin cycle.

The Calvin cycle

In simple terms, the Calvin Cycle is a series of chemical reactions that plants use to capture CO2 from the air and turn it into sugar. This sugar provides the energy plants need to grow. These light-independent reactions use the energy stored in ATP and NADPH to convert CO2 into glucose. The glucose is then used by the plant for various purposes, including growth, reproduction, and other metabolic processes.

Why Are CO2 Bags Good For Cannabis Plants?

CO2 bags can have a significant impact on cannabis plants when used in the right conditions. Elevated CO2 levels can enhance photosynthetic processes. Basically, when cannabis plants have access to more CO2, they can potentially grow faster and produce higher yields because the rate of photosynthesis can also increase, which creates more efficient energy production. The extra energy can be used by the plants for faster growth, stronger stems, and larger leaves.

Faster Plant Growth With CO2 Bags

With more energy available, cannabis plants can grow at an accelerated pace. This faster growth can translate into shorter vegetative periods and a quicker transition to the flowering stage.

Bigger Yields With CO2 Bags

When provided with optimal growing conditions and higher CO2 levels, cannabis plants can also produce more buds and potentially give growers larger harvests. This is particularly beneficial for growers looking to maximise their yield.

Enhanced Stress Tolerance With CO2 Bags

Elevated CO2 levels can also help cannabis plants better tolerate environmental stresses, such as heat or water stress. This can be particularly useful in grow spaces with High-Pressure Sodium (HPS) lights or less-than-ideal temperature control (such as loft space in summer).


General Advice for Cannabis Growers Considering Adding CO2 Bags To Their Setup:

It’s important to note that simply increasing CO2 levels is not enough to maximise growth. For best results you should try to optimise the following environmental conditions:

Light Intensity and Quality Spectrum

Adequate light intensity and an appropriate spectrum are crucial for photosynthesis. Cannabis plants usually require full-spectrum light with a higher concentration of blue and red wavelengths.

Photosynthetic Photon Flux Density (PPFD): Ensure your plants receive adequate light intensity, as this is crucial for photosynthesis. Cannabis plants require a PPFD of 800-1,000 µmol/m²/s during the flowering stage for optimal growth. Investing in a high-quality full-spectrum LED grow light can help you achieve the desired PPFD.

Optimum Temperatures

Cannabis plants have an optimal temperature range for photosynthesis, which is generally between 70-85°F (21-29°C). Temperatures outside of this range may reduce the efficiency of photosynthesis and negatively impact plant growth. However, with elevated CO2 it is possible to run slightly higher temperatures without impacting plant growth (but it may affect your terps).

Ideal Humidity

The optimum relative humidity (RH) to aim for is typically between 40-60%. Higher humidity levels can promote the growth of mould and other pathogens, while lower humidity levels can lead to poor nutrient uptake and slow growth.

Ample Nutrients and Water Availability

Cannabis plants require the right balance of water and essential nutrients, including nitrogen, phosphorus, potassium, calcium, magnesium, and sulphur, as well as various micronutrients. These nutrients must be provided in the correct ratios to support optimal growth.

Monitor the EC of your nutrient solution to ensure optimal nutrient availability. An EC of 1.2-2.0 mS/cm is typically recommended for cannabis plants, but this may vary depending on the growth stage and specific strain. It’s generally best to follow the nutrient regime that the nutrient manufacturer recommends.

Vapour Pressure Deficit 

Vapour Pressure Deficit (VPD): VPD is a measure of the difference between the amount of moisture in the air and the amount the air can hold when saturated. Maintaining an ideal VPD with elevated CO2 can improve stomatal conductance, plant transpiration rates, and overall plant health. A VPD of 0.8-1.2 kPa is generally recommended for the vegetative stage, while a VPD of 1.2-1.5 kPa is ideal for the flowering stage.

Ideal leaf temperatures 

Leaf temperature plays a critical role in stomatal conductance and plant transpiration rates. An optimal leaf temperature range for cannabis plants is 68-77°F (20-25°C). Stomatal conductance is essential for efficient CO2 uptake during photosynthesis. Maintaining ideal leaf temperatures helps keep stomatal conductance optimal and ensures that the plant can take full advantage of elevated CO2 levels.

You can easily measure leaf temperatures with a laser heat gun (infrared thermometre).

General Advice for Growers Considering Buying CO2 Bags:

Assess Your Growing Environment

Before investing in CO2 enrichment products. It is best to try and make sure your grow environment meets the basic requirements for healthy cannabis growth. This includes proper lighting, temperature, humidity, and nutrient management.

Choose The Right CO2 Enrichment Product

There are several CO2 enrichment products available, such as CO2 exhale bags, CO2 generators, Smart CO2 Bags, Small Canisters and Enhancer CO2 Dispersal bottles. Each product has its advantages and disadvantages, so select the one that best suits your needs, budget, and growing space.

Monitor CO2 levels

Invest in a CO2 monitor to measure and maintain the desired CO2 concentration in your grow space. Cannabis plants can benefit from CO2 levels between 1,200-1,500 ppm (parts per million), but higher concentrations can be detrimental.

Ventilation and air circulation

Make sure you have got good ventilation and air circulation in your grow space to prevent CO2 buildup and maintain a healthy environment for your plants. This will also help control humidity and temperature. 

Be careful to try and balance intake and exhaust fans because you do not want to vent all of the CO2 before plants get a chance to use it. This is a fine balance, but with a good CO2 monitor you will get the hang of managing air flow and air replacement.

Should I Add CO2 Bags To My Cannabis Grow? 

Ambient CO2 levels are around 350-500 PPM  and this is not ideal for cannabis plant growth. Elevated CO2 levels can enhance cannabis plant growth and produce bigger yields. However, it is vital that environmental conditions are managed properly. So make sure things like light intensity, temperature, humidity, and nutrient management are also optimised is crucial to get the best results.

If you have your space dialled in then including a CO2 Bag will undoubtedly improve your growing experience, so give it a go and see the results for yourself.