Question about the grow...whats your ppfd?? Ive heard some people say stuff like "Dr bugbee recommends 1200/1200(ppfd/CO2 ppm)"
Is your ppfd that insanely high to demand CO2 in veg? I have no hands on experience FYI; just noticed something out of the norm to what I've read. If your ppfd is below 850, would the CO2 be a waste in veg? Save till your mid flower?? Just speculating growmie
No. You get an immediate increase in yield by adding CO2 even at any stage of growth other than germination and even at modest light levels.
Most inputs in the grow environment do not increase yield once they reach the "sufficiency" stage. Once a plant gets enough water, stop. Once a plant is in the sufficiency zone for nutrients, adding more nutrients is expensive and, eventually toxic.
Temperature has a direct impact photosynthesis which leads to an increase in yield. The best evidence based information is that yield increases up to 85±°, though secondary metabolite levels are seriously degraded once temperature exceed 78° in flower.
The two inputs that improve yield past the sufficiency level are CO2 and light. If you're in a grow environment where you can run CO2, add it. You'll get about a 30% increase in yield at 1200-1500 ppm of CO2.
Below is a graphic from the Chanrda paper (attached) that shows the change in net photosynthesis ("net P") at varying temperatures, light levels, and CO2 concentrations.
A lot of people in the cannabis world looked assumed that because net P started to roll off at about 500µmol, that the indicated that there was no sense in growing cannabis at light levels much higher than 500-600µmol.
That was an erroneous assumption.
Research clearly indicates that, as long as light is the limiting factor, yield increases in an almost linear manner as light levels increase. The highest levels of light that I've seen reported as being used was 2000µmol and the researcher, Mitch Westmoreland, discussed below, stated that, even at that level, yield continued to increase.
Going back to your issue — if you can add CO2, do so because it's cheap and will give about a 30% increase in yield at any light level. Interestingly, if CO2 levels drop by 20%, yield drops by 40% or somesuch. Too little CO2 is brutal. (At the current level of 420ppm for CO2, we are still not far from the dreaded 280ppm below many crops fail.)
Most personal growers can't add CO2 so the next best thing is to turn up the dimmer and get as much light on your grow as your plants can handle. The light saturation point for cannabis, which is the light level above which adding more light does not increase photosynthesis, is considered to be 800-1000 and it is strain dependent as well as being limited by how well a grow is set up.
If you look at the lighting recommendations from many light vendors, those values that are recommended in flower will result in light levels in the 1k range. Vendors recommendations are conservative in veg and there's no need to be. I routinely grow my plants at high light levels (600µmol by day 30 and increasing to 1k shortly as soon as possible thereafter) and have very good outcomes.
The most concise source for some of this information is in the You Tube videos that Mitch Westmoreland, PhD candidate under Bruce Bugbee, released in late 2023 in which he shares some of the results of the research that he's done for his thesis. It's chock full of good information and really is a "how to" do help ensure that you get the most from your cannabis grow. Highly recommended.
