24 hours vs 18 for veg

Erb

Well-Known Member
Most green plants are classified as either C3 or C4 which represents how carbon(C) is used during photosynthesis.

C4 plants temporarily store carbon dioxide(CO2) over the dark period to use for photosynthesis during the day. C4 plants slow down photosynthesis once the stored CO2 is used up and they need to gather it from the air. Which is why trees slow down photosynthesis in the afternoon even though the sun is still bright. This does NOT apply to cannabis.

C3 plants(cannabis/veggies) gather CO2 only during the light period when they are photosynthesizing. During the dark period these plants only use oxygen for their metabolic life processes. They don't uptake CO2, nor do they use it. As soon and as long as the light is on, C3 plants gather and use CO2 for photosynthesis.

C3 plants also have the ability to use higher concentrations of CO2 than what is found in the air. If the light is bright enough and the plants have sufficient nutes, their growth rate will accelerate from it(2000ppm vs. 400ppm of CO2), which increases yield. They can do this continuously, wihtout a dark period throughout the vegetative stage.

The dark reaction is a process of photosynthesis that takes place in both darkness and light. It uses ATP and NADPH molecules that hold energy absorbed from light to break apart CO2 into it's base components. Because it's called a dark reaction and can occur in the dark, some people(Jorge) have said darkness is needed for this to occur. This Is Not So.

Again people get anthropomorphic with their plant needs. People need rest, so plants must too. This is false as well. Light means growth. Scientifically. Although 18/6 will shock your plants less when you switch to 12/12, it's a personal choice whether you would rather sacrifice a little growth for a quicker adjustment or less photo confusion. If you want to save money or energy that's
a personal choice too. Do what you need to do to make your growing scenario work.
 

Moon Shadow

Well-Known Member
whoo where did that come from and can I see more

I want to try it but don't know how

Love the avatar where could I get one like it

hemp makes more paper per acre than trees per all them other things in the leaves
 

joekikass

Well-Known Member
ive uesd both 18 and 24 h cycles with co2 and have found that 24 h's light take about a week off my veg times and reduce to 12/12 over a couple days to avoid to much shock .
 

HarvestMaster

Active Member
had to read that first one 3 times before I fully understood it. That is great to know. Personally I have used both and only cut lights for purposes of saving energy when needed. I always thought the 18/6 cycle was better for no known reason, but now have a better understanding on the true difference. Thanks for the info...
 

HarvestMaster

Active Member
only objection I would have is Looking at one strain that was currently growing I just switched the lights to 18/6 2 weeks before flowering and noticed no difference in the growing. CO2 is in this room. But this strain is a very slow grower so maybe on other strains this would be a factor.
 
i love this post, logical scientific information, with no "im experienced, I KNOW" bullshit, thanks, answered alot of questions, funny how alot of people are confused by such basic information once you know it
 
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