How to Use CO2 to Increase Yields in Your Medicinal Plants Grow

December 15, 2021

Benefits of Adding Extra CO2

  • Bigger yields, faster growth – If you’ve maxed out the other limiting factors (especially light), CO2 can make your plants grow faster and enhance your yields.
  • Plants can stand higher temperatures – A CO2-rich environment makes plants more hardy against heat. Maintaining 1200-1500 PPM of CO2 in the air allows medicinal plants to handle up to 95°F (30°C). For growers with a lot of hot bright lights, this can make it easier to keep the temperature within a range that plants can take.
  • Security – CO2 enrichment involves sealing your grow room, which can be beneficial for security because you’re not venting out hot or smelly air. Certain methods of adding CO2 like using a CO2 generator will also create smells that help cover up the odor of medicinal plants directly.
  • Extremely effective with HPS grow lights – Adding CO2 works best in a hot environment with powerful grow lights that produce a lot of infrared light. When adding CO2 with HPS, plant growth can increase by up to 20%. Other HIDs like LEC/CMH grow lights also get a big boost from extra CO2. Big LEDs get a moderate increase of growth, especially in a hot grow space. Small LEDs or fluorescent grow lights (CFLs or T5s) benefit the least from CO2 enrichment.

How to Inject Extra CO2 Into Your Grow Room

1.) Use the Right Grow Light for Your Space

In order for Co2 injection to be effective, you should use powerful grow lights like HPS or LED. A good rule of thumb is you should have 7,500-10,000 lumens per sq foot in your grow area to get the full benefits of enriching with CO2 when supplementing with 1200-1500 PPM. You need high-powered grow lights like HPS bulbs, LEC/CMH, or bigger LEDs for this rule to hold true.

If you’re using less light, you’ll need less CO2 to be effective, though you won’t get as big a growth increase as if you were using stronger lights.

To figure out if you have enough light to supplement up to 1200-1500 ppm of CO2, determine out how many lumens your bulbs gives off. Then find the square footage of your space (length x width). Lumens/square footage should equal 7,500-10,000 (note: LEDs are not typically measured in lumens so it’s better to look at the wattage).

Examples of setups with enough light for CO2 injection up to 1500 PPM with HPS, LEC, or LED. These amounts are considering the amount of electricity used from the wall, not any kind of “equivalent” light. For example, with a “600W equivalent” LED you should look at the true power draw (usually listed in the product details).

2.) Seal Your Grow Space (optional)

Regular air only has about 400 PPM of CO2 so if you don’t seal your grow area, any CO2 you add will slowly leak out. While this may not be important if you only plan on adding relatively small amounts of CO2, if you want to maintain high levels of CO2 up to 1200-1500 ppm of CO2 in the air, you should seal your grow space in order to prevent yourself from wasting lots of CO2.

You should seal your grow room to keep all the extra CO2 inside if you’re adding a lot of CO2

Some things to keep in mind when sealing your grow space:

  • Temperature – If you’re supplementing at the highest levels, many growers recommend maintaining temperatures between 85°F (30°C) and 95°F (35°C) in your grow space for extra CO2 to be most effective, though it’s important to watch plants closely for signs of heat stress as some plants can handle heat better than others.
  • Humidity – You should keep humidity below 60% RH to prevent mold and other problems. I mention this because plants give off water  through their leaves, which means controlling humidity low can be difficult in a sealed room. For bigger operations, you will likely need a dehumidifier.

If You Do Want to Seal Your Room, Get the Right Hood/Reflector!

Most growers need to cool their lights to keep temperatures in the right range. When choosing a reflector for your grow light, it’s important to decide whether you want one that can be cooled via ducting without letting any of that air get inside the grow room and bring down your CO2 levels. Your other option is to use an air conditioner to cool the room.

3.) Add CO2 By “Raining” It On Your Plants From Above

CO2 should “fall” onto plants from above if possible. CO2 is heavier than air and will sink to the bottom of your grow area, so you want your CO2 to float down onto your plants. That means any CO2 enrichment method should be located above your plants.

You’ll get the best results when you make sure CO2 is evenly dispersed over your plants. A small fan on the floor pointed upwards can help keep the CO2 circulating through the room and floating over your plants.

There are 6 popular ways of adding CO2 to the air of your grow area…

  • Compressed CO2 <– Recommended
  • CO2 Generator <– Dangerous (don’t put one of these in your home!)
  • Fermentation
  • CO2 Bag
  • Compost
  • Dry ice

CO2 Generators and Compressed CO2 are the most effective ways to add CO2 to your grow area, but since generators are dangerous I only recommend using compressed CO2. The other options are not dangerous, but also not very effective.

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