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has anyone tried an 18/12 light cycle?

  • Thread starter Thread starter lvstealth
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has anyone tried an 18/12 light cycle?

lvstealth 64 Replies 14,099 Views
Page 3 of 4 · Replies 41–60 of 65
#41
I am indoor 12/12. Reg seeds.
I actually do 11.5hr on an 12.5hr off till two weeks before cut. Last two weeks I do 13hrs on 11hr off a bulking effect. Hope yer grow goes well!!
 
#43
Coconutz said:
To give it 18hrs you must exceed 12hrs, 12hrs ± can't be broken while maintaining flowering.
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You can go 8h dark and still flower.but its all about the rythm you can still flower if your timer breaks and you give it 2 days 24h light soo as long as it hits its 8h to start leaching flower hormones....
The hormon is allways produced but after 8h its "overflowing" that gives the flowering reaction
 
#44
This subject seems to come up from time to time. The general consensus seems to be it makes no noticeable difference.
 
#45
I just posted this on my own thread on my 18/12 hour grow I'm currently doing. I thought y'all should read this.

Thread '18/12 Light schedule in Flower especially during stretch' https://www.thcfarmer.com/threads/18-12-light-schedule-in-flower-especially-during-stretch.173191/

I wrote
"Originally I was only going to use this during the stretch. So looking at 10 days as a length of time. The math shows the following.

10 * 24 = 240 hours

In 12/12 that is 120 hours of light and 120 hours of dark.

In 18/12 the cycle is 30 hours.
240÷30=8 cycles

8×18=144 hours of light
8×12=96 hours of darkness.
144-120=24 hours more light during the same period.
That is 2 full extra lights on periods of 12 hours than the 12/12 during the same 10 days.
That's huge.
That's 20% more light. More photosynthesis more sugar production more growth of leaves, stems and BUDS. I would imagine it would affect the roots also."
 
#46
Yamon said:
I just posted this on my own thread on my 18/12 hour grow I'm currently doing. I thought y'all should read this.

Thread '18/12 Light schedule in Flower especially during stretch' https://www.thcfarmer.com/threads/18-12-light-schedule-in-flower-especially-during-stretch.173191/

I wrote
"Originally I was only going to use this during the stretch. So looking at 10 days as a length of time. The math shows the following.

10 * 24 = 240 hours

In 12/12 that is 120 hours of light and 120 hours of dark.

In 18/12 the cycle is 30 hours.
240÷30=8 cycles

8×18=144 hours of light
8×12=96 hours of darkness.
144-120=24 hours more light during the same period.
That is 2 full extra lights on periods of 12 hours than the 12/12 during the same 10 days.
That's huge.
That's 20% more light. More photosynthesis more sugar production more growth of leaves, stems and BUDS. I would imagine it would affect the roots also."
Click to expand...
Soo it worked? You could flower
 
#47
amneziaHaze said:
Soo it worked? You could flower
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I had already used the 12/12 putting my plant into flower. This seems to be the best way to initiate flowering. Stay with 12/12 until pre flowers indicate you are in flower.
I myself was already midway through the stretch when I conceived of the idea to do this 18/ 12 schedule.
This thread was mostly all I found on Google re: something as extreme as 18/12. I saw things like 13/11.
But nobody talking about a different cycle length than 24 hours.
So that's what I'm doing. I'm trying it and talking about it while learning.

My plant is still growing vigorously in flower after switching to 18/ 12.
 
#48
Okej soo still testing.growing vigorosly can still be reveg
 
#49
amneziaHaze said:
Okej soo still testing.growing vigorosly can still be reveg
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It won't reveg. Theoretically lol.
During the dark cycle after the conversion of Pfr to Pr Florigen is created. That's what initiates and keeps the plant in flower. Once the original signal (florigen) happens you are in flower. The signal will eventually need to be renewed but it's not on a 24-hour schedule.
It's like the gunshot starting a race. Once you do the gunshot it doesn't matter how long the race is. The signal has been given and the processes are all started.

I'm putting most of my thoughts and research and of course how it's unfolding on my thread about this grow at 18/12. There's a link to an article by a Professor Lee. Reveg does not seem to be an issue. I have reveged a massive plant after HARVESTING it before.
That is a very cool process to watch
 
#50
Are you guys seriously saying switching to a 18/6 mid flower will not make a plant reveg

Lmfao

Yamon said:
Hi Y'all.
I have started an 18/12 schedule starting around day 17 of flower. I would have started at day 10 but hadn't thought of it yet.
Some thoughts to consider.

Extra Light in Flowering Doesn’t Revert Cannabis to Veg — Here’s Why​

Physiology-based explanation to debunk the “extra light = reversion to veg” myth:​


1. The real trigger: darkness, not light
Cannabis is a short-day (photoperiod) plant. Flowering is triggered and maintained by uninterrupted periods of darkness, not by the number of hours of light. As long as the plant receives the minimum dark window (usually ~12 hours for photoperiod strains), it will remain in flower.

2. Why people get it wrong
A common myth is that any light longer than 12 hours will force the plant back to veg. This misunderstanding comes from oversimplifying the 12‑12 schedule taught in textbooks. While 12‑12 is standard for flowering, extra light does not erase the dark signal. The plant senses darkness cues through phytochrome pathways, not by tallying light hours.

3. Natural variability
Plants evolved under variable conditions: cloudy days, shading, storms, or even volcanic dust can drastically change light intensity and duration. Cannabis has survived and flowered for millions of years under these conditions, which demonstrates that it is highly resilient and flexible in its light usage. What matters is the continuity of darkness.

4. Effects of extended light

More light hours = more energy for photosynthesis, allowing faster node stacking, taller stretch, and more biomass.

As long as dark periods are maintained, flowering continues normally.

Resin, trichome, and bud development are generally not negatively affected; in fact, extra energy may enhance overall growth.


5. Bottom line

Flowering depends on darkness continuity, not on capping light at 12 hours.

Extra light during flowering does not revert the plant to veg, it simply provides more energy to build bigger, stronger colas.

Reversion occurs only if the plant’s dark period is interrupted or shortened below the flowering threshold.


Conclusion: Growers can safely experiment with slightly longer light periods during flowering (e.g., 18‑12) to maximize stretch and energy capture, as long as the dark period remains uninterrupted.
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What a load of ai slop & bollox

I’m outa here this place has become home for ai bro science
 
#51
Gmix said:
Are you guys seriously saying switching to a 18/6 mid flower will not make a plant reveg

Lmfao


What a load of ai slop & bollox

I’m outa here this place has become home for ai bro science
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Doesn't say 18/6 man before you go off perhaps just read what it says it says 18/12 that's completely different
 
#53
Yamon said:
Doesn't say 18/6 man before you go off perhaps just read what it says it says 18/12 that's completely different
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Ok I get what your saying now

Must admit ai posts makes me angry that aside sry I think I need a few more hrs sleep sry
 
#54
Gmix said:
Ok I get what your saying now

Must admit ai posts makes me angry that aside sry I think I need a few more hrs sleep sry
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Admittedly some of that is generated by AI but after lengthy conversations and diving into a topic. I will often create for my own use to put in a notes file. I contribute by asking further pointed questions.
I then request a summary and have that edited to my satisfaction
It's one thing to just go hey ChatGPT can I grow cannabis with 18 hours of light and 12 hours of darkness and then post the response vs having a conversation for 5 hours and then putting something together as a summary.
In case you didn't notice I'm actually growing a plant day 21 of flower that has been on the 18/12 schedule since day 10 of flower. It's growing perfectly.
 
#55
@Yamon

Pretty embarrassed making the mistake I did

Thanks for being the bigger man & not going off on one

Have fun
 
#56
Day 26 of flower. Been running 18 hours of light and 12 hours of darkness for 9 days now.

My plant is loving the schedule change. It had no stress reaction. In fact it seemed happier. 4 days after changing to 18 hours of light. On day 21 I did a schwazing removing all the fan leaves. Again no stressful reaction even though I'm growing in soil. Nutrition and water uptake are great.
The cola's are stacking incredibly fast.
I have about 40 really big colas and 20 or more smaller ones.
All of them are getting tons of light now.

I've already posted the link to the thread for my current grow under 18/12.
 

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#57
I have changed my light cycle to 20 hours of light and 12 hours of darkness.
Everything is working fantastic.
I did a major Schwazzing on day 21 of flower. I am now on day 29. My plant didn't didn't stress in fact it indicated it loved being defoliated. Now all light goes directly to the sugar leaves and therefore directly to the buds themselves.
I did leave about 20 large fan leaves that are down low on the perimeter.
They will never be in the way of any of the colas
 
#59
I've increased the light time by 1hr after vegging on 12-12, some plants went to shit and some didn't mind, the transformation to partial veg was slow it taken me ages to actually see what was happening to them, it ruined 3 of 5 seeds, 3 clones and 2 seeds didn't mind the increase.

It'll certainly be interesting to watch the progress I hope it does work out good luck 👍
 
#60
Coconutz said:
I've increased the light time by 1hr after vegging on 12-12, some plants went to shit and some didn't mind, the transformation to partial veg was slow it taken me ages to actually see what was happening to them, it ruined 3 of 5 seeds, 3 clones and 2 seeds didn't mind the increase.

It'll certainly be interesting to watch the progress I hope it does work out good luck 👍
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Well that's some different strategy that's for sure. I'm not quite sure why you were vegging on 12/12. When you're in veg you want to grow your architecture. And you want to grow that as much as you can so you do 18 hours of light. My seedlings and young veg plants are under 24 hours of light. What I'm doing is making lighting changes in flower.
After flowers already started. That tells you you plant is fully committed to being in flower. Then I increase the light from 12/ 12 to 18/ 12 and now I'm at 20/12.
The extended light drives more photosynthesis for all parts of the plant. I believe that the momentum gained throughout that long light cycle is another element that adds to the synergy.
But like all more advanced techniques you want to make sure you have a healthy plant.
Thanks for the well wishing dude.
 
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