Refresh Checked Unchecked Menu Search Shopping bag Geolocation Person Facebook Instagram Twitter YouTube Info Icon CBC Icon CBC Shape CBD Icon CBD Shape CBG Icon CBG Shape THC Icon THC Shape THCV Icon THCV Shape Loading…

How to Use CO2 to Increase Yields in Your Marijuana Grow

February 21, 2017
Carbon dioxide (CO2) is a gas that fills our atmosphere, and it’s essential for plants to complete the process of photosynthesis wherein plants convert CO2 into energy. High levels of CO2 in a cannabis garden can result in stronger plants with increased yields – if introduced correctly. So how do you control and add CO2 to your cannabis grow room for the best possible end product?

How Does CO2 Work for Plants?

Indoor marijuana garden

Plants extract CO2 from the atmosphere via the plant’s stomates, which are the pores that plants “breathe” through. Photosynthesis begins as the plant uses CO2 in combination with light bulbs or light from the sun to produce both sugar and oxygen. The sugar is used by the plant to grow while the oxygen is released back into the atmosphere.

Increasing CO2 levels in your cannabis garden will allow your plants to create more energy – if you provide adequate lighting as well. Again, light is the second requirement to create energy for your plants, meaning you must match your CO2 levels with your lighting. However, before we dive into how this is done, there are a number of other considerations to make before investing in a CO2 system.

Who Should Use CO2 Systems for Cannabis?

Analog indicator

The benefits of introducing CO2 into a grow space are well known and widely accepted. However, if you’re a novice grower and/or under a tight budget, there might be a number of ways for you to initially increase your yields before investing in a costly CO2 system. Make sure you first know how to:

  • Grow a healthy garden with a quality product
  • Prevent and/or treat mold and pest infestations
  • Set up a secure, sealed grow space
  • Use an adequate high-powered light system
  • Utilize quality strain genetics
  • Use quality nutrients and growing mediums

If you have a handle on the above points, you should be ready to try increasing your yields using added CO2.

How to Introduce Additional CO2 to a Garden

There are multiple ways to introduce CO2 to your garden, but most methods do not guarantee controlled ppm (parts per million, used to measure CO2 levels in atmosphere). For this reason, it’s important to invest in a quality CO2 setup. If the systems below are too costly or demanding for your space, you may consider holding off on CO2 supplemented grows until you’re ready to make the jump.

CO2 Generators

CO2 generators, which look something like patio heaters, produce carbon dioxide by burning propane or natural gases. They can be set up to automatically power on or off when CO2 levels reach a specific ppm. Natural gas or liquid propane are very easy to acquire, but the burning of these gases produces heat which can be difficult to regulate in small grow spaces. Because of this, CO2 generators are better suited for large grow spaces with equipment for climate control.

Compressed CO2

Compressed CO2 tanks can be acquired at hydroponic stores, compressed gas facilities, or even home brewing stores. In this case, the CO2 is produced by the manufacturers and is collected and compressed into tanks that can be then made available for purchase. This allows you to introduce controlled quantities of CO2 into your garden via emitters without having to own a CO2 generator. The benefit of this setup is that without a CO2 generator, you’re no longer producing heat when releasing CO2 into your garden. For this reason, compressed CO2 is ideal for smaller grow spaces.

How to Use CO2 in Your Cannabis Garden

Marijuana flower buds.

CO2 levels in our atmosphere are around 400 ppm. Interestingly, studies show CO2 levels can continually increase plant growth as ppm reach upwards of 10,000. Note that once CO2 is above 3,000 ppm it starts to become dangerous for humans to breathe, and at 5,000 ppm it is considered lethal.

Most gardeners have found that when you are producing high-quality light in your garden, a CO2 level of 1,200 to 2,000 ppm will increase the growth of your plant significantly. Additionally, when using CO2 your plants can handle a higher average temperature – around 85-90 degrees Fahrenheit. Be aware that if your CO2 levels are too high for the amount of light or heat generated in the garden, you will see your plants become damaged from excess CO2.

The CO2 emitted should ideally fall from above the garden, as CO2 is heavy and will sink to the ground. Using fans will help keep the CO2 moving around the room and make it available for more plants to absorb. CO2 should only be emitted during the time that the lights are on; plants photosynthesize while it is dark out.

Growing cannabis is an ever-changing practice. Taking on a challenge such as introducing CO2 could evolve your garden, taking it to the next level. Have you spent any time with CO2 in your garden? Take the opportunity to share your experiences in the comments section below.

Trevor Hennings's Bio Image

Trevor Hennings

Trevor is a freelance writer and photographer. He has spent years in California working in the cannabis industry.

View Trevor Hennings's articles

  • Hey Trevor,

    Great info, Did you find any negatives from using CO2? Such as the bud being harsher on the lungs?

    For some reason some growers I used to know always debated wether the CO2 actually made the bud more carcinogenic and less ‘natural’.. Did you find any evidence to suggest that while researching this piece?


    • Mark Lemon

      Old wive’s tales. Supplementing CO2 only increases yields, not potency, quality or taste.

      • Ok thank you.

        • Richard Crownover

          Anyone know if a room is at 1200 PPM CO2, how long does it take for the CO2 to degrade to a point of needing to replentish?

  • Sturge

    if light has to be balanced with the co2, what should be the ppm for a 600 watt bulb? 8×8 room with light mover?

  • Mark Lemon

    Having worked closely with cannabis growers for several years at CO2Meter dot com, here are some additional tips first-time cannabis growers may find useful:

    1. Experts agree that supplementing CO2 is not a quick fix for improve plant yields. Proper soil/medium, nutrients, watering, light, temperature and cleanliness must be achieved first. Only then will you see the 10-25% yield improvements enhanced CO2 can provide.

    2. Different plant species react differently to increased CO2 levels. CO2 levels below 400ppm (fresh air) or above 1,500ppm will reduce cannabis plant growth. If your grow room is sealed, over the course of a day the CO2 level will drop below 400ppm. If you’re not supplementing CO2 to start, you must have a constant flow of fresh air into the grow room.

    3. Temperatures above 27°C (80°F) over time results in elongated stems and lower yields of mature plants. Buy a thermometer. If your lights are too hot, use a fan to dump the hot air and fix this problem before you worry about CO2.

    4. Gas CO2 generators are dangerous. Start with a CO2 boost bucket, then as you get better at growing, move up to compressed CO2 tanks and electronic regulators.

    5. Expert cannabis growers disagree about the optimum level of CO2 for cannabis growth. You can find arguments for 800ppm, 1,000ppm, 1,200ppm and 1,500ppm online. We recommend starting at 800-1,000ppm, then adjusting your CO2 levels over time with experience.

    6. If you’re using compressed CO2, point a fan directly at the end of the tubing from the regulator to mix the CO2 into the air. For larger grow rooms, connect the regulator to tubing with pin-holes strung around the ceiling so that the CO2 will “drop” on the plants (CO2 is heavier than air).

    7. If you’re using compressed CO2, purchase a plug-in timer or a day/night CO2 controller to control your CO2 regulator. Never run CO2 during the dark period. It’s a waste of money.

    As a final note, the article got its decimal points mixed up on dangerous levels of CO2. 1,000ppm of CO2 in your grow room is 0.1%. You’ll never notice it. 10,000ppm is 1% CO2, and at the worst it will make you drowsy, like driving a car with the vents closed. At 30,000ppm (3%) you’ll notice physical effects like reduced hearing or shortness of breath, and at 80,000ppm (8%) CO2 is deadly.

    • Could you generally describe what the CBD output of just one healthy plant (cloned from good stock) might be after a 12 week pampered grow indoors? We are high altitude (over 6,500 ft) and our CO2 normal levels are in the low 300’s.

    • Kris Kline

      I use a propane heater at night to keep my greenhouse from dropping below 40°F. In the morning my CO2 ppm is 8,000 and drops throughout the day down to 800. I’m thinking I should be purging my greenhouse in the morning with outside air, down to possibly 1,800 ppm?

      • Mark Lemon

        Unless it is hurting your crops, I wouldn’t recommend it. Since you’re ending the day at 800 ppm and aren’t adding additional CO2, you can’t afford to “throw away” the 6,000 ppm you’ve paid for in energy costs every morning.

  • Jesse Beau Angelia


  • Greg Simøn

    “Plants photosynthesise while it is dark out”

    Wrong, other way around. Typo, I assume. Leafly should edit this as to not mislead new-timers.

  • WhodaThunkit

    Fact or Fiction?
    I was told “using too much CO2 will make a dangerous product”
    Aside from quality, my concern is health