Adding carbon dioxide to your grow room is a powerful way to get faster growth and bigger yields. But this isn't a simple trick for beginners. Using CO2 grow techniques is an advanced strategy that only works when other conditions—like your lighting and environment—are already dialed in. It’s not the right move for every grower or every setup. Before you start, it's crucial to understand if this method is a good fit for your space and what it takes to get it right.

What is CO2?

Carbon dioxide is used by plants in photosynthesis. In high concentration, it can be harmful for humans, but it is absolutely essential for plant growth. This article is going to cover everything you need to know about how you can use carbon dioxide for your grow space, and help in deciding whether it will actually be beneficial for you.

How does CO2 boost growth in a grow tent?

As elaborated above, carbon dioxide is essential to all plants. The natural concentration of CO2 in the environment is approximately 400 ppm. If you’re growing in an outdoor space, you cannot increase the concentration beyond this. If you’re growing indoors though, the limitation disappears and you can introduce more carbon dioxide in your grow tent. When you increase the concentration of carbon dioxide to a range of 1,200-2,000 ppm, your plant yield will shoot up and the growth of your plants will accelerate significantly. The heat resistance of your plants will also receive a boost.

Grow Lights and Carbon Dioxide

The lighting in your grow tent is the crucial factor in determining whether your plants can benefit from introducing extra carbon dioxide. Using high intensity grow lights like CMHs, LEDs and HIDs will allow you to reap the benefits of using carbon dioxide. If your grow lights do not have enough power, carbon dioxide supplementation will not help. CFLs and T5s are excellent grow lights for supplemental purposes, or propagation. But they’re not enough for creating the conditions in which carbon dioxide supplementation can benefit your plants.

Introducing CO2 into your grow room

Setting up a system for introducing carbon dioxide into your grow space is simple enough, and will probably take an hour at most. There are different ways in which you can do this:

CO2 Tank & Regulator Kit

Using a standard tank and regulator kit, is the method most growers use for carbon dioxide supplementation.CO2 tanks usually weigh 25-50 pounds and are made of aluminum. The tank contains compressed CO2 and can be placed outside your grow tent to conserve space. The tank is connected to a regulator that you can plug into a CO2 controller or the wall. This subsequently connects to tubing that is placed above the plants through out the roof of the tent. This way the carbon dioxide can be directly emitted onto the plants to maximize absorption. As the name suggests, the regulator enables you to adjust the amount of CO2 that’s flowing into your grow tent. A CO2 tank is an optimal solution if you’re growing your crop in a tent.

Why Use CO2 in Your Grow Room?

Think of CO2 as a supercharger for photosynthesis. Plants naturally pull carbon dioxide from the air to create the energy they need to grow. The air around us typically contains about 400 parts per million (PPM) of CO2. While that’s enough for plants to survive outdoors, an indoor grow space gives you a unique advantage: you can control the environment. By increasing the CO2 concentration, you give your plants a key ingredient to work with, allowing them to process light and nutrients more efficiently. This can lead to significantly faster growth and more robust plants, but only if you have the right setup to support it.

The Benefits of CO2 Supplementation

The primary reason growers add CO2 is to get more out of their plants, faster. When you supplement CO2 in a well-managed environment, you can see some pretty impressive results. According to research from CANNA Gardening, enriching the air with CO2 can increase plant growth by over 30%. This translates directly into shorter growing cycles and bigger, heavier harvests. It’s not just about quantity, either. Plants grown in an optimized, CO2-rich environment often show improved overall quality and resilience. They can become stronger and better equipped to handle environmental stressors, giving you healthier plants from start to finish.

Understanding the Risks of Low CO2

Just as high levels of CO2 can accelerate growth, low levels can bring it to a screeching halt. In a sealed grow room or tent, your plants can quickly use up the available carbon dioxide. Without proper ventilation or supplementation, CO2 levels can plummet. This starves your plants of a crucial element for photosynthesis. In fact, if CO2 levels drop by just 25% from the ambient level, your plant's growth can slow down by more than 50%. This is why managing CO2 isn't just about adding more; it's also about ensuring your plants never run out of this essential gas.

Key Considerations Before Adding CO2

Before you invest in a CO2 system, it’s important to understand that it’s an advanced technique, not a quick fix. CO2 supplementation is most effective when every other aspect of your grow room is already dialed in. Think of your setup as a chain; it's only as strong as its weakest link. If your lighting, temperature, humidity, or nutrient regimen isn't optimal, adding CO2 won't produce the results you're looking for. It works in synergy with other environmental factors, so you need a solid foundation before you can truly benefit from enrichment.

CO2 Is Not a Magic Fix

It's easy to get excited about the potential for massive yields, but CO2 only delivers on its promise when your plants have everything else they need. Your plants can only use the extra CO2 if they also have enough light to power photosynthesis and the right amount of water and nutrients to build new tissue. If your lighting is weak or your plants are stressed, they simply can't take advantage of the enriched atmosphere. Start by mastering the fundamentals of your grow, and then consider CO2 as the final piece to maximize your garden's potential.

The Need for a Sealed Environment

To effectively supplement with CO2, you need a sealed or "closed-loop" environment. If your exhaust fan is constantly running and pulling fresh air into your space, it will also pull out all the expensive CO2 you're pumping in. This makes high-quality grow tents an excellent choice because they are designed to be sealed, preventing leaks. By closing off intake and exhaust vents (at least while the CO2 is running), you can maintain the high concentrations needed for your plants to thrive, making your investment much more efficient and effective.

Understanding Diminishing Returns

More isn't always better, and that's certainly true with CO2. While increasing CO2 from 400 PPM to 1,200 PPM can have a dramatic effect, pushing it from 1,200 PPM to 1,500 PPM will have a smaller impact. This is the principle of diminishing returns. The first boost provides the most significant benefit. As you continue to add more, the gains become smaller and smaller. Finding the sweet spot for your specific plants and setup is key to getting the best return on your investment without wasting resources or potentially harming your plants.

Optimal CO2 Levels and Timing

Getting your CO2 levels right is a balancing act that changes as your plants grow. Different growth stages have different needs, and providing the correct concentration at the right time is crucial for success. You also need to know when to turn the CO2 on and off, as plants only use it when they are actively photosynthesizing. Running your CO2 system 24/7 is not only a waste of money but can also be harmful. Proper timing and precise levels will ensure your plants get exactly what they need, when they need it.

CO2 Levels by Growth Stage

Your plants' CO2 requirements will evolve throughout their lifecycle. Young plants need less, while mature, flowering plants can handle much higher concentrations. Tailoring the PPM levels to each specific phase will help you support your plants' development and maximize their growth potential at every step. Here’s a general guide to follow:

Seedling Phase

Seedlings and clones are delicate and don't require high levels of CO2. Their root systems are still developing, and they can't take full advantage of an enriched environment yet. For this early stage, aim for a modest concentration of around 600-800 PPM. This provides a gentle nudge without overwhelming the young plants.

Vegetative Stage

Once your plants enter the vegetative stage, they start growing rapidly and can handle more CO2. This is when you can begin to ramp up the concentration to fuel their vigorous foliage development. A range of 800-1,200 PPM is ideal for promoting strong, healthy stems and leaves, setting the stage for a productive flowering phase.

Flowering Stage

During the flowering stage, your plants' metabolic rate is at its peak, and their demand for CO2 is highest. This is where supplementation truly shines. You can increase the levels to 1,200-1,500 PPM to support robust flower and fruit production. Maintaining these levels, especially during the first few weeks of flowering, can lead to significant gains in final yield.

Final Weeks of Flowering

In the last one to two weeks before harvest, it's a good practice to taper off your CO2 supplementation. The plants' growth is slowing down as they focus their energy on ripening. Reducing the CO2 levels back down to ambient (around 400 PPM) can help signal the end of the growth cycle and save you money on CO2 refills.

When to Start and Stop Supplementation

Plants only use CO2 during photosynthesis, which means they only need it when the lights are on. You should set your CO2 system to turn on shortly after your grow lights switch on and turn off just before they go out. There's no benefit to running CO2 during the dark cycle. Most growers begin supplementation once the plants have a well-established root system and are a few weeks into the vegetative stage, continuing through the peak of the flowering phase for maximum impact.

Harmful CO2 Levels to Avoid

While CO2 is essential for growth, too much of a good thing can be harmful. If concentrations get too high, they can become toxic to your plants. Levels above 2,000 PPM can cause damage to the leaves and stunt growth, completely negating the benefits. It's crucial to use a reliable CO2 monitor and controller to keep levels within the optimal range and prevent accidental overdoses that could jeopardize your entire crop.

The Importance of Consistency

Plants thrive on stability. Wild fluctuations in CO2 levels can cause stress and hinder their growth. Aim to keep the concentration as consistent as possible during the "lights on" period. Using an automated controller is the best way to achieve this. It will measure the PPM in the room and release CO2 as needed to maintain your target level, ensuring your plants have a steady supply to fuel their growth day after day.

Balancing CO2 with Key Environmental Factors

Successfully using CO2 is all about synergy. To unlock its full potential, you must balance it with the other critical elements in your grow room: light, temperature, and humidity. When you increase CO2, you're essentially giving your plants the fuel to go faster, but they also need a bigger engine (more light) and the right operating conditions (higher temperature and balanced humidity) to use that fuel effectively. Getting this balance right is the key to achieving the explosive growth that CO2 supplementation promises.

Matching CO2 to Light Intensity

Light is the energy that drives photosynthesis. The amount of CO2 your plants can use is directly tied to the amount of light they receive. If you add more CO2 without increasing light intensity, your plants won't be able to use it. This is why CO2 supplementation is typically reserved for grows using powerful LED grow lights or HIDs. As a rule of thumb, the more intense your lighting, the more CO2 your plants can process. You must ensure your lights are powerful enough to justify the expense and effort of CO2 enrichment.

Adjusting Temperature for CO2 Enrichment

With higher CO2 levels, plants can photosynthesize more efficiently at higher temperatures. Their stomata (the pores on their leaves) don't need to open as wide to take in CO2, which means they lose less water through transpiration. This allows them to thrive in warmer conditions that would normally stress them out. With CO2 levels above 1,000 PPM, many plants can perform well in temperatures up to 95°F (35°C). This gives you a wider operating window and can be especially helpful in managing heat from high-intensity lights.

A Note on Terpenes and Temperature

While plants can handle higher temperatures with CO2, it's important to consider the impact on your final product. For many aromatic plants, the volatile compounds responsible for scent and flavor (terpenes) can begin to evaporate at temperatures above 78°F (26°C). If preserving these delicate aromas is a priority, you may want to keep your temperatures in a more moderate range, even when supplementing with CO2.

Balancing Humidity and Vapor Pressure Deficit (VPD)

Vapor Pressure Deficit (VPD) is the difference between the amount of moisture in the air and how much moisture the air can hold when saturated. It's a critical metric that influences how your plants transpire, or "breathe." When you raise the temperature to match your CO2 levels, you also need to adjust the humidity to keep the VPD in the optimal range. Proper VPD ensures your plants can efficiently transport water and nutrients from their roots to their leaves. Using environmental controls like humidifiers or dehumidifiers is essential for maintaining this delicate balance.

Equipment, Setup, and Safety

Setting up a CO2 system correctly is just as important as understanding the science behind it. The right equipment will ensure accurate and consistent delivery, while proper placement and safety protocols will protect both you and your plants. From calculating your room's needs to calibrating your monitors, taking the time to get the details right will pay off in the long run. A safe and well-maintained system is the foundation of any successful CO2-enriched grow room.

Calculating Your Grow Room's CO2 Needs

Before you buy any equipment, you need to figure out how much CO2 your space requires. The calculation is straightforward: multiply the length, width, and height of your grow room in feet to find its cubic volume. Then, multiply that volume by your target CO2 concentration in decimal form (for example, 1,200 PPM = 0.0012). The result is the cubic feet of CO2 needed to reach your target level. This number will help you choose the right size tank or generator for your setup.

Proper Equipment Setup

A reliable CO2 system consists of a few key components: a CO2 source (like a tank or generator), a regulator to control the flow, tubing to deliver the gas, and a monitor/controller to automate the process. The controller is the brain of the operation; it constantly measures the CO2 level in the room and opens or closes the regulator to maintain your desired PPM. This automation is crucial for consistency and prevents dangerous over- or under-shooting of your target levels.

CO2 Monitor Placement

Where you place your CO2 monitor is critical for getting accurate readings. It should be positioned near the center of the room, at the same height as the top of your plant canopy. This ensures it's measuring the air that your plants are actually using. Avoid placing it too close to a fan, an exhaust vent, or the CO2 emitter itself, as this can lead to false readings and inefficient operation of your system.

How CO2 Behaves in a Grow Room

It's helpful to remember that CO2 is heavier than air. When you release it into your grow room, it will naturally sink downwards. For this reason, it's best to run your delivery tubing along the ceiling or high on the walls, allowing the CO2 to gently fall over your plants. A small oscillating fan placed on the floor and angled upwards can also help circulate the air and ensure an even distribution of CO2 throughout the entire canopy.

Safety and Maintenance Protocols

Working with CO2 requires a commitment to safety. High concentrations of CO2 can be dangerous for humans and pets, so you should never enter the grow room when the system is actively releasing large amounts of gas without proper ventilation first. Regular maintenance is also key. Check your equipment daily for any signs of malfunction, especially if you are using a propane or natural gas generator, to ensure it's burning cleanly and safely.

Regular Monitor Calibration

Your CO2 monitor is your most important tool, but its sensors can drift over time and become inaccurate. Most high-quality monitors need to be calibrated periodically to ensure they are providing correct readings. Follow the manufacturer's instructions for calibration, which often involves taking the sensor outdoors to a source of fresh air (which has a known CO2 level of about 400 PPM) to reset its baseline. Regular checks will keep your system running accurately.

Maintaining a Clean Environment

A sealed, CO2-enriched grow room creates a warm, humid environment that is not only great for plants but also for pests and diseases. Because there is little air exchange with the outside, any problems that arise can spread quickly. Therefore, extreme cleanliness is non-negotiable. Be diligent about cleaning your space, sterilizing equipment between cycles, and carefully inspecting your plants for any early signs of trouble. A proactive approach to hygiene is your best defense in a closed-loop system.

Is a CO2 Burner Right for Your Grow?

A CO2 burner is the next popular alternative if you’re growing in aproducts for making natural CO2grow room. Any natural gas and liquid propane when ignited, produce CO2. The burner itself is comprised of 2-10 burners. The burners are installed in a metal container which is placed at the ceiling of the room. It’s positioned right over your plants. The burner consists of as few as two, or as many as ten burners. This “burner” is a metal box that is hung from the ceiling of the grow room above the canopy of the plants. A tank that contains a natural gas or liquid propane is connected to a regulator which in turn is connected to a carbon dioxide controller. When the gas is released, the burners ignite it which produces the carbon dioxide. The caveat of this process is that it generates a lot of heat in your grow space. You have to take this into consideration, particularly if you’re growing in a small space or if you live in an area that has high temperatures. In this scenario, maintaining the optimum temperature would prove to be a challenge and hassle for you. You might consider in investing in an air conditioner for your grow room then.

Natural Methods

There are lots of ways in which you can produce supplemental carbon dioxide through natural means. We have a range of products for making natural CO2. These are far more convenient to use compared to purchasing tanks or burners and setting them up. There are bags and pads that contain CO2 producing fungi, which can be hung above your plants. They react to humidity levels in your room and produce CO2. Natural CO2 methods are markedly inexpensive and convenient. Most growers usually use them for backup in case your CO2 tank runs out or your burner stops functioning. We strongly suggest that you don’t use natural methods as the main method of producing CO2 for your garden. The main reason is that the output cannot be controlled or shut off by CO2 controllers.

CO2 Controllers

CO2 controllers are essential in this process. You need CO2 controllers to maintain a consistent concentration levels of CO2 in your grow space. CO2 controllers are connected to your CO2 producing devices for this reason. Once the ideal concentration level is reached, they shut off that device. Conversely when concentration levels drop, they turn your devices back on again. Their function is similar to that of a thermostat.

CO2 has to be introduced at the right time of the day as well. Photosynthesis only occurs during the day. Plants produce carbon dioxide during the night, just like humans, so introducing carbon dioxide at the point in time would be harmful. Therefore, CO2 controllers are equipped with photocells for determining whether it’s day or night. This allows you to keep your grow lights and CO2 devices in sync.

Additional information for using CO2 in your grow spaces

There are a couple of more things to take into consideration when introducing supplemental CO2 in your grow space

Closed loop grow spaces

You need to ensure that your grow tent or room is completely sealed. It is a common practice amongst growers to use an inline fan in the garden to regulate humidity and heat. If you plan on using supplemental CO2 for your plants, you will have to stop using it as it will remove the CO2 from the room before it has an effect. Your grow room has to be a closed loop. You can only use an exhaust fan for situations in which CO2, humidity and temperatures reach unsafe levels. Check out this article about grow room atmosphere and ventilation to better understand ventilation systems and open/closed loop rooms.

Safety and Precautions

Carbon dioxide in high concentrations can be extremely harmful. So be careful and ensure that your equipment is installed properly and your grow tent / room is sealed! It’s best to invest in a CO2 alarm or detector. Remember that carbon dioxide is colorless and odorless, so you won’t find out until you feel the effects!

Final Thoughts

If you want to grow sizeable plants that have a high yield, then CO2 supplementation is definitely for you. Coupled with the right lighting, you can significantly boost the growth of your plants. Still unsure about how to use CO2 for your grow space? We’re just a click away at Groindoor! Our team of experts can help you decide exactly what you need for your garden. Learn about the ideal growing environment for your crop here as well!

Safety Checks for CO2 Burners

While CO2 is great for your plants, high concentrations can be dangerous for people. This is a safety aspect you absolutely can't overlook. Because carbon dioxide is both colorless and odorless, you won't know if levels have become unsafe until you start feeling the physical effects. To prevent this, it's crucial to invest in reliable environmental controls, specifically a CO2 alarm or detector for your grow room. This device will alert you if CO2 levels reach a harmful threshold. Always double-check that your burner is installed correctly and that your grow space is properly sealed to prevent any leaks into your living areas. Taking these precautions ensures you can enrich your garden's environment without compromising your own safety.

Air Exchange Requirements for Burners

To get any benefit from a CO2 burner, you must create a "closed-loop" system. This means your grow room or tent needs to be completely sealed off from outside air during supplementation. Many growers use inline fans and ventilation to manage heat and humidity, but you'll need to turn those off while your CO2 burner is active. If you leave an exhaust fan running, it will simply pull all the CO2 you're adding right out of the room before your plants have a chance to use it. Think of it like trying to heat a room with all the windows open—it's just not effective. Your exhaust fan should only be used to vent the room when CO2 levels, heat, or humidity become too high, not for constant air exchange.