TL;DR?
-IF IT WORKS FOR YOU FINE. MANY GROW IN 24/0 AND IF YOU'RE HAPPY WITH YOUR YIELD THEN KUDOS.
-A plant takes light for food. When it's "full," it takes excess unused light and expends the energy as heat.
-If a plant is full, and is unable to expend incoming photons as heat, bad things happen.
-Plant goes from growth mode to defense mode, PSII inactivates, harmful photo-oxidation occurs, wasteful Calvin Cycle reactions/photorespiration take place
-Photo-respiration results in a NET LOSS of carbon and nitrogen, which can limit growth
-Plants with high nitrogen (aka veg phase) tolerate excess light
-Plants with low nitrogen (24/0 in the flowering phase? *SLAP*) tolerate excess light poorly
-MYTH: A plant "grows" when the lights are on.
-MYTH: Photosynthesis is good, it happens when light is on, so nonstop light must be good.
-MYTH: Plants grow in 18/6 because they are reaching for light.
-MYTH: Plants grow faster, shorter, bushier in excess light because they like it
-FACT: A plant "makes food," when the lights are on. It then USES this food to grow.
-FACT: Plants grow shorter and bushier because they are possibly stunted by metabolic changes due to excess light
-WHAT IS EXCESS LIGHT FOR CANNABIS? Unknown. Anecdotal evidence suggests 20/4, but surely varies between strains.
-Based on my research (as a Biochemistry/Microbiology double major *flex*) I HYPOTHESIZE that even 23/1 is superior to 24/0.
-When researching 24/0 vs 18/6, every CANNABIS-RELATED site was mixed 50/50, and typically was non-researched opinion based on personal experience or word of mouth.
every NON-CANNABIS RELATED site was OVERWHELMINGLY AGAINST 24/0, regardless of species.
For the record, it's 24/0, not 24/7. Saying 24/7 is like saying I give my plants 18 hours of light 6 days a week. 24 hours of light, 0 hours of dark. (Yes, I get that you mean light 24 hours, 7 days a week aka constant
) ANYWAY. First some science, then my opinion.
"Low light intensity can be compensated by increasing the time (duration) the plant is exposed to light, as long as the plant is not sensitive to day-length in its flowering response. Increased hours of lighting allow the plant to make sufficient food to survive and/or grow. However, plants require some period of darkness to develop properly and thus should be illuminated for no more than 16 hours. Excessive light is as harmful as too little light. When a plant gets too much direct light, the leaves become pale, sometimes sunburn, turn brown, and die. Therefore, during the summer months, protect plants from too much direct sunlight. "
---[SIZE=+1]
An excerpt from the Texas Master Gardener Handbook
Compiled at Texas A&M University by
Douglas F. Welsh, Extension Horticulturist
Samuel D. Cotner, Extension Horticulturist
Texas A&M University
"[/SIZE]Other short-term responses to increases in light intensities include increases in cyclic electron transfer rates, activation of the Calvin cycle, and photorespiration. Long-term responses include reductions in effective light intensities by thickening and tilting of leaves, accumulation of anthocyanins, and movements of the chloroplasts [reviewed by: [
4]]. A reduction in light harvesting can be achieved by reducing the size of the effective light-harvesting antenna, while energy utilization can be increased by up-regulation of the "dark" reactions. In addition, plants have scavenging systems that neutralize light-induced reactive oxygen species (ROS). ROS are generated, to some degree, at all light intensities, but especially when the intensity exceeds the capacity of the plant's photon utilization mechanisms."
In layman terms, a plant has built in mechanisms to compensate for excess light, to a certain extent.
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Improper excess light energy dissipation in Arabidopsis results in a metabolic reprogramming
http://www.biomedcentral.com/1471-2229/9/12
First, to clear the record just because they're called "dark reactions," doesn't mean they only take place during the dark, or at night. They're called dark reactions because they are "light-independent," aka they convert carbon into glucose and other compounds through reactions that don't require light. Some of these reactions are enzymatic-ally controlled via electron flow, which doesn't happen in the dark.
Second, photosynthesis is the process of converting CO2 + H2O -> Glucose (food) + O2. So logically, how can you feed a plant infinitely? Eventually it is going to reach it's metabolic equivalency where it doesn't want any more damn food, just like you don't want to constantly be eating cheeseburgers until you explode. Once that happens the plant's metabolism has to shift away from normal. If it's got all it's food and it can't give any more excess off as heat, it doesn't have a choice but to undergo metabolic change.
I'm having a hard time finding the post that made me switch from 24/0 to 18/6. Basically, when the lights are off you gain root mass, and the plant's metabolism is chuggin along normally, as it would in the wild. Better roots = more pot essentially. It included a table of some experimentation that showed root growth peaks between 16/8 and 20/4. From my own experience, the roots in my DWC didn't really grow until I gave them some dark time. From then my roots doubled in length in 3 days, but without a control group it's worthless data.
There are other factors for my personal choice though. First, I have small cabinets so heat is an issue; any time the plants get a break from the 82 degree temps is fine by me. Second, I have small cabinets
So I'm more focused on getting a nice root mass than actual plant growth. That way once it hits 12/12 the plant will already have well developed roots to suck up all those nutes when it's making my buds and really starting to stretch out.
I smoked a J before writing this so it appears to have turned into a rant. I hope some of you find it useful
i don't have a ph meter as of yet. (still trying to find one) don't really know where to look that would be half decent on price & we don't really have much for garden centers where im at especially at this time of year. i also need a rh meter, hard trying to guestimate everything.
