Inicio » Crop articles » How to Use CO2 in Cannabis Grows
If you notice your plants get weak or yellowish at any moment, or worse, then stop using CO2 immediately and try and find out what’s going wrong. Either too much CO2 is accumulating or we’re giving them too little and it’s too warm. Make sure you follow the parameters exactly or using it can actually do more harm than good. If done properly, your harvest will be ready a few days earlier and you’ll get a higher yield.
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.
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.
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.
- 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.
You can use any way of dispensing CO2, connected to a CO2 controller that will shut off the flow of CO2 once it reaches a certain level, and open it again once it gets too low. If all you have is a normal CO2 meter, you can still control the CO2 levels by opening and closing a solenoid valve using a timer. (Solenoid valves are valves that are opened and closed with an electromagnetic charge). Whichever kind of system you use, you must know the exact PPM (parts per million) of CO2 in your grow room.
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.
If you have any questions feel free to leave a comment.
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 answer to this need is the enzyme RuBisCO, which binds to CO2 molecules and transfers them to the photosynthetic machinery. Under ambient CO2 concentrations (about 400 ppm) and otherwise favorable conditions, the activity of RuBisCO is the limiting factor on photosynthetic productivity. This means that when temperature or light intensity rises above the cannabis plant’s tolerance level, RuBisCO is unable to keep up with the CO2 demands of the reaction sites and the excess energy becomes stressful. By adding additional CO2 to the equation, we boost the activity of RuBisCO. It encounters CO2 molecules more often and can transfer them more efficiently, allowing the plant to extend productivity beyond normal limits.
CO2 fertilization allows cannabis to thrive at higher temperatures and utilize higher light intensities, but these two factors need to be considered together. Light comes with more heat, especially in HID illuminated environments. Both parameters shift the photosynthetic machinery into higher gear and CO2 enrichment allows it to run faster and cleaner. However, even with CO2, pushing too hard with light and/or temperature can send your plants into stressful conditions.
CO2 molecules present within the leaf need to be channeled to provide a constant supply of fuel for photosynthesis.
One of the most hotly debated aspects of CO2 fertilization in cannabis cultivation is the proper concentration of CO2. The only cannabis-specific research done is this area is presented in Dr. Chandra’s publications, where he found that raising CO2 concentration to 700 ppm resulted in an instantaneous increase in photosynthetic productivity of 38-48 per cent, depending on strain. Unfortunately, his work doesn’t discuss the effects of CO2 fertilization at concentrations higher than 750 ppm.
As cannabis legalization continues to progress and the markets in legal states mature, the physiology of cannabis will hopefully be studied to the same degree as other crops. With these efforts will come a better understanding of how to best use CO2 fertilization in cannabis cultivation. Until that time, my advice is to enhance bloom in the 1,200-1,600 ppm range, with 1,400 ppm as a good rule of thumb.
Another consideration is that, over time, many C3 plants fail to maintain the productivity gains that they initially experience with CO2 fertilization. Understanding this goes back to RuBisCO activity.
The general recommendation for maximizing CO2 fertilization in greenhouse crops is to raise the growth temperature by five to 10 degrees Fahrenheit above the ideal temperature in the absence of CO2 enrichment. For cannabis, this means that the ideal bloom temperature is shifted into the mid to high 80s. It is important to note that ambient grow temperature does not usually represent the temperature that the plant canopy is experiencing.
The concentration at which CO2 becomes detrimental to plant health varies widely between species. Tomatoes, for example, have an upper threshold of about 2,000 ppm, while chrysanthemums experience stress at concentrations greater than 1,200 ppm. In the absence of research to clarify the issue, my view is that our favorite plant likely falls on the higher side of the continuum, as cannabis is a highly productive annual capable of explosive growth.
In addition to facilitating the passage of CO2, stomata also regulate water loss through transpiration. Leaves close stomata to reduce water loss, but doing so reduces CO2 uptake. It’s a dry world out there, and C3 plants constantly regulate stomatal openings to balance CO2 uptake against water loss. Due to the large moisture gradient between leaves and the surrounding air, taking in CO2 is costly in terms of water.