How to use CO2 in cannabis grows is one of the many questions that we’re frequently asked. CO2 is essential for cannabis plants and every other plant, as to them CO2 is like oxygen and they need it to survive. Cannabis plants can deal with CO2 levels of up to 600% the amount that there naturally is in the air around us. Basically, it makes their cells multiply much faster, so if you use extra CO2 during the flowering period you’ll get buds that are much thicker than usual which, if done correctly, makes for a much bigger yield.
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Here’s a guide on what you should do and the strength of the CO2 in your grow room from the 21 st day of flowering onwards. EC levels apply if you’re growing in hydro or aeroponics. If you want to measure them in soil you’ll need to measure the water that comes out from the bottom of the flowerpot once you’ve watered; if more is needed you can add it in the next watering, and if it’s too high then the next watering should just be water on its own.
CO2 needs to be introduced into your room through a silicone tube, with one outlet per plant near the bottom of the trunk. You can also use a 2m tube to go around the grow area with holes facing the center, towards the plants.
If you don’t use CO2 in the right way you could end up with yellowing plants, or long stretched out plants with hardly any buds. You’re going to need to know what you’re doing to implement CO2 correctly. There are many systems that can be used to get more CO2 into your crop; beginner systems that are used as a little extra boost and don’t require much care, and then professional systems that measure the PPM of CO2 that there is in the atmosphere. Professional systems are obviously much more effective and efficient than beginner ones, but they also require more work and attention.
Once everything’s installed and ready to go, you’ll need to know exactly how to use CO2. Well, it’s used in the flowering period from the 21 st day onwards, once the buds start to take shape and are slowly popping up at the tips of all of the branches. You’ll need to change your air filtration so that the extractor only works for around 15 minutes an hour because if it’s left on it will get rid of all of the CO2 and all of the effort will have been for nothing. You can use another timer to program the CO2 controller so that it doesn’t turn on when the extractor is on. CO2 should only be administered when the lights are on, as the extraction should be on constantly when the lights are off.
- Day 21 of flowering: Begin with 800 PPM, and keep it at that when the extractor isn’t on. When watering, you’ll need to raise the EC every time to raise the CO2 levels. For this first week you’ll need about 1.7 EC using normal irrigation water.
- Day 24 of flowering: Raise the CO2 to 850 PPM, and the EC to 1.8.
- Day 27 of flowering: CO2 to 900 PPM and EC to 1.9
- Day 29 of flowering: From this day onwards you’ll need to increase both CO2 and EC every two days. 950 PPM and 2.0 EC.
- Day 31 of flowering: 1000 PPM and 2.1 EC.
- Day 33 of flowering: 1050 PPM and 2.2 EC
- Day 35 of flowering: 1100 PPM and 2.3 EC
- Day 37 of flowering: 1150 PPM and 2.4 EC
- Day 39 of flowering: 1200 PPM and 2.5 EC. From this day onwards, increase levels every day.
- Day 40 of flowering: 1250 PPM and 2.6 EC
- Day 41 of flowering: 1300 PPM and 2.7 EC
- Day 42 of flowering: 1350 PPM and 2.8 EC
- Day 43 of flowering: 1400 PPM and 2.9 EC
- Day 44 of flowering: 1450 PPM and 3.0 EC (this is the max EC level)
- Day 45 of flowering: 1500 PPM and 3.0 EC
- Day 46 of flowering: 1550 PPM and 3.0 EC
- Day 47 of flowering: 1600 PPM and 3.0 EC
- Day 48 of flowering: 1650 PPM and 3.0 EC
- Day 49 of flowering: 1700 PPM and 3.0 EC
- Day 50 of flowering: 1750 PPM and 3.0 EC
- Day 51 of flowering: 1800 PPM and 3.0 EC – This is the max CO2 level you can have in your grow room. Continue the rest of the flowering period without raising anything, and make sure to do that root wash 10 days before harvesting.
CO2 increases your plants cell walls and multiplies them rapidly, but make sure that you fertilize them also as they’ll end up light and pretty down looking if they get a lot of CO2 but not any nutrition. They’ll also need a slightly higher heat than usual, around 28-32ºC so that the water in the leaves can evaporate slightly faster and the plants can absorb the nutrients straight away. Basically, we want the plants to absorb the nutrients but get rid of the water fast. You’ll need a dehumidifier to lower the ambient humidity to normal levels, because once the temp is raised and your plants begin evaporating water, humidity levels will raise a lot.
How to Use CO2 in Cannabis Grows; here's a step by step guide on how to correctly use CO2 to get the most out of your plants.
The amount of CO2 in the air has a profound effect on the rate of photosynthesis and plant growth. Photosynthesis speeds up as the amount of CO2 in the air increases, as long as there is enough light to power it (to an upper limit). Photosynthesis slows to a crawl and virtually stops at a CO2 concentration of around 200 ppm. Lacking CO2, plants continue respiration and growth for a short time, until their sugars are used up; then they slow down their metabolism to conserve energy. Only when more CO2 is available can the plant processes continue.
At 100 ppm CO2 respiration and photosynthesis are equal so there is no net loss or gain.
The easiest way to supply carbon dioxide is to use a CO2 tank kit.
Cannabis uses CO2 in the presence of light. Photosynthesis occurs when the plant receives light. The marijuana plant draws in CO2 from the air by tiny openings on the undersides of leaves called stomata. They function much like pores in the skin, but have guard cells that can open and close. They regulate the absorption of water, gas, oxygen, (O2), and CO2 into the plant, as well as the evacuation of water and O2 from the plant.
Outside of the grow tent, the air conditioner and CO2 tank are installed.
The increase is moderate, but significant between 800 and 1200 ppm.
In this garden, air is enriched as it passes through the tubes.
CO2 tanks are a common way to raise CO2 levels in a garden, but there are other ways:
Instead of using a tank, you can use a meter that regulates a CO2 generator that burns propane or natural gas.
Learn why the amount of CO2 in the air has a profound effect on the rate of photosynthesis and marijuana plant growth.