Indoor gardeners provide their plants with light energy and plant nutrition while mimicking the atmospheric conditions most conducive to plant growth. To maximize the garden’s yield and quality, growers are continually seeking methods to manipulate one or all of these factors.

Carbon dioxide is used by plants during photosynthesis. Professional growers have been adding it to their gardens’ atmospheres for years as a way to boost plant growth. When used correctly, supplemental CO2 is a great way to manipulate the atmospheric conditions in the growroom and increase the rate of photosynthesis.

This increased rate equates to faster growth and larger yields. To get the most out of supplementation, growers must understand how to most efficiently use CO2 in their gardens.

Whether or Not to Supplement Your CO2 Levels?

When considering using supplemental CO2, the first thing a grower needs to do is analyze the growing environment to see if this will be cost effective. Fully automated growrooms—growing environments where light energy, plant nutrition and the atmospheric conditions are all in check—are good candidates.

Growers should think of supplemental CO2 as the icing on the cake—one of the last additions to a growroom. For example, if a grower is debating whether to purchase an air conditioner to adequately cool the room or a CO2 system, they should purchase the air conditioner. It is far more important to provide the plants with the proper temperatures than additional CO2.

Most growers should only seriously consider CO2 systems after they have tackled the lighting, ventilation and nutrition for their gardens; otherwise, the garden will suffer and the CO2 system will not be cost effective.

Types of CO2 Supplemental Systems

There are several ways a grower can provide additional CO2 to a growing environment. A closer look at some of the available options can give a grower an idea of which system, if any, best suits their needs.

Mycelium-based Systems

Mycelium-based CO2 systems come in all shapes and sizes, including buckets, bags, boxes and mats. These systems rely on a fungus and a food source for the fungus (usually some sort of compost). Mycelium is the vegetative part of a fungus and as it grows it produces CO2 as a by-product.

Mycelium-based systems have a few advantages. They are relatively inexpensive, allowing a grower to try them out without making a large investment. Mycelium-based CO2 systems are usually lightweight, which means they can be placed or hung anywhere in the garden. They also do not produce any heat, which makes them perfect for small environments like grow cabinets or grow tents.

The disadvantages of mycelium-based systems are that they only cover a relatively small area, there is no way to control their outputs and they need to be replaced every grow cycle. Generally speaking, mycelium-based systems are best suited for hobby gardeners growing in confined areas.

Compressed Tanks and Regulators

Compressed CO2 in aluminum or steel tanks is another method of carbon dioxide supplementation. For this system to operate correctly, the grower needs to buy a regulator in addition to the actual tank. The regulator is a device that controls the rate at which the CO2 is emitted from the tank. Special regulators designed for horticultural purposes can be found at your local indoor garden retailer.

The regulator is electronically controlled and can be connected to a timer or a monitor/controller. There are a few advantages to compressed tanks in comparison with other supplementation devices. The tanks hold a lot, which means these systems work for larger garden environments than mycelium-based devices. Compressed CO2 will also not add any heat to the garden space.

These devices can be purchased for a reasonable price and, unlike mycelium-based devices, will not need to be replaced, just refilled. The refill costs associated with tanks are minimal.

On the other hand, the tanks can be cumbersome and have to be moved in and out of the garden each time they need to be refilled. In urban areas, finding an indoor garden retailer or gas supplier is fairly easy, but for more remote locations it may be difficult to locate a place to get the tanks refilled.


CO2 burners are devices that burn propane or natural gas and produce CO2 as a by-product of that combustion. Burners come in many shapes and sizes and are most commonly used in large indoor gardens or greenhouse applications. One key advantage is they can easily cover a large area.

Propane is readily available, making refills a snap, and natural gas CO2 burners can be even easier to maintain because the natural gas can be run directly from the home or main line, which means the grower does not need to refill anything. The biggest disadvantage of burners is the excess heat they create.

For most indoor gardeners, excess heat can be a problem as they are already operating extra hardware to cool lighting systems. The other disadvantage associated with burners is the initial cost. Carbon dioxide burners are the most expensive route a grower can take for supplementation, but for larger gardens, burners will quickly pay for themselves.

Optimizing Return with a Supplemental System

Regardless of the type of system a gardener chooses to use, he or she must use it correctly to optimize the return. There are a few factors that contribute to an effective supplemental CO2 system. Growers who understand these factors will not only obtain consistently large yields but will also quickly recoup their investment.


A grower with an automated CO2 device will gain the most return on the equipment, with the exception of mycelium-based systems, which cannot be controlled. Automation goes a long way in maximizing efficiency and maintaining consistency. Plants will respond much better over time to consistent levels of CO2 in the atmosphere. Carbon dioxide is only used by the plants for photosynthesis when the lights are on.

This is why most controllers are equipped with a photosensor that automatically turns off the device during the dark cycle, reducing wasted CO2. Controllers incorporated into an atmospheric controller or able to be connected to an atmospheric controller will take efficiency to the next level.

These devices will bypass the CO2 system while the exhaust fans in the ventilation system are running, stopping CO2 from being exhausted out of the room and eliminating waste. The high-end controllers contain special microprocessors with built-in algorithms for learning the atmospheric conditions of a growroom. These devices will intuitively make adjustments to maximize consistency.

For example, let’s say every day at 4 p.m. there is a drop in the level of CO2 within the room. Over time, these devices will automatically increase the CO2 level at 3:45 p.m. to combat the reduction in CO2 at 4 p.m.

Concentration in the Atmosphere

With an automated system, the grower is able to set the desired concentration of CO2 in the atmosphere. The concentration is usually measured in parts per million or PPM. In normal air, the concentration is around 300 to 400 ppm. This can be slightly higher in urban areas where there are higher levels of air pollution. Plants will respond positively to any amount above the ambient levels in the air.

Growers new to CO2 supplementation can begin with a concentration of 700 to 1,000 ppm. For more advanced growers, a level of 1,100 to 1,500 ppm is the norm. Concentrations above 1,500 ppm are rarely used in indoor horticulture as it becomes counterproductive once the concentration gets too high.


Another important factor in maximizing supplemental CO2 in an indoor garden is the temperature of the growing area. Think of photosynthesis as a chemical equation where each compound in that equation can affect the other. This is what happens with CO2 and temperature. As CO2 levels increase, the ideal temperature for plant growth increases as well.

This means a grower supplementing CO2 will have to increase the growroom’s operating temperature to best use the increased amounts. Growers who choose a concentration of 700 to 1,000 ppm should keep the lights-on temperature around 75 to 82°F. More advanced growers who choose a concentration of 1,100 to 1,500 ppm should keep the lights-on temperature around 82 to 89°F.

Growers with hydroponic systems who are supplementing the higher level need to take extra precautions to ensure the nutrient solution’s temperature is kept cool. Water chillers are essential for hydroponic growers looking to supplement the maximum amount of CO2.

Increasing CO2 levels within a growing environment is a great way for growers to increase growth rates and maximize a garden’s potential. There is no shame in starting out with a lower amount of it and then slowly increasing the concentration until you find what works best for your garden. For a well-functioning growroom, CO2 supplementation offers growers one more way to supercharge their gardens and enhance the growing experience.