Effects of different photoperiods on flowering.

LJB said:

I know one grower / scientist with a working theory about 32 hour photoperiod.... That is 18 on, 14 off during bloom. He swears by it.

I have nothing else to add.

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I changed from that 32 hour diurnal to a 28 diurnal last grow. Now I am using 16/12; not 18/14. I have done a lot of research into this (more lately) and it seems 18 hours is less ideal than 16 hours. I reduced the nightlegth from 14 hours to 12 hours to shorten the diurnal considering I reduced the daylength by 2 hours.

All the best.

I've heard of switching to 14 on 10 off during weeks 6-7 of flowering.
Saw it in a grow video somewhere.

Also, there is the 23.5/12 method making a week 5 days. Never tried that one...

Most of what people "hear" and are "told" is BS. Look at this thread for example, many people are talking about < 10 hours of nightlength to flower! There is no reason to use a 24 hour diurnal, thus if we increase the diurnal we can offer 14/12, 16/12, 16/16, whatever.

HTH (what I wrote above should be what people trust, not the other info in this thread or elsewhere...I can offer full references backing up all my claims)

secondtry said:

I changed from that 32 hour diurnal to a 28 diurnal last grow. Now I am using 16/12; not 18/14. I have done a lot of research into this

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Why is 16/12 superior to 12/12? Not doubting, just don't know what the advantage is.
Are we talking the same number of calendar days to finish for each? Or same amount of "on" time?
What type of timer is used to do this? I have interval timers that do minutes, so assume it's the same principal, only w/ hrs?
Thanks ----------- CB

Hello,

The main benefits are greater net photosynthesis, carbon assimilation, carbohydrate partitioning, etc, and in cannabis that seems to equate to increased growth and yield. Below I posted my references on the science. I am not sure what you mean by "on" time. Each day is 28 hours, not 24; so a week is 196 hours, not 168 hours. We can change the hours of one full day (daylength plus nightlength) because cannabis isn't dependent upon circadian rhythm, it is dependent upon hours of darkness for flowering and for not-flowering.

You could order special timers do to this digitally which is a real bonus, maybe $50-100. But you could also use a regular timer because we are only changing the daylength, not the nightlength, thus once the daylength pass the 4 hour mark you can turn the dial back 4 hours, but that means you need to be there each daylength.


Here is some references from my Zotero:

Oh yea,

I use an hour or darkness mid-daylength to give the plant a rest and lower leaf temp, which means I really give the plants 15 hours of light in a 16 hour daylength. For example you can put an hour of darkness starting at hour 4.5 of daylength so when you spin the timer back it basically hits half way through the day. Or you a digital timer.

secondtry said:

Hello,

The main benefits are greater net photosynthesis, carbon assimilation, carbohydrate partitioning, etc, and in cannabis that seems to equate to increased growth and yield. Below I posted my references on the science. I am not sure what you mean by "on" time. Each day is 28 hours, not 24; so a week is 196 hours, not 168 hours. We can change the hours of one full day (daylength plus nightlength) because cannabis isn't dependent upon circadian rhythm, it is dependent upon hours of darkness for flowering

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Sorry I wasn't clear. By "on" time I meant day (or lights ON).
Maybe an example would help. We know we have to have the 12 dark. Now we have 3 choices --- I know we have more, but bear w/ me ---- 8 or 12 or 16 hrs of light. W/ 12 as our base, would the lower input expense compensate for what the smaller 8hr schedule would yield? And conversely, would the extra 16 expense be justified by its increase? Really only increasing by 7% the total "on" time, so gains wouldn't have to be that great to justify. Be interesting to try w/ the right timer ----- can't see my inconsistent ass adjusting it everyday.
Thanks for all the references. Great to have them in one place. I'll try to wade thru them soon.
CB

LJB said:

Who rated my posted as not being helpful and didn't bother to respond it?

The grower asked about using more than 12 hours of light during the bloom cycle.

I explained why people attempt do this which also explains why it might not work and also mentioned someone else's working theory.

What is anti-helpful about this? The title of the thread is " Effects of different photoperiods on flowering"...

edit: I see it was Maj.PotHead.

So what's the problem with the information that was posted? Explain your actions for the rest of us.

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i thought your post was informative man....

Carboy said:

Sorry I wasn't clear. By "on" time I meant day (or lights ON).
Maybe an example would help. We know we have to have the 12 dark. Now we have 3 choices --- I know we have more, but bear w/ me ---- 8 or 12 or 16 hrs of light. W/ 12 as our base, would the lower input expense compensate for what the smaller 8hr schedule would yield? And conversely, would the extra 16 expense be justified by its increase? Really only increasing by 7% the total "on" time, so gains wouldn't have to be that great to justify. Be interesting to try w/ the right timer ----- can't see my inconsistent ass adjusting it everyday.
Thanks for all the references. Great to have them in one place. I'll try to wade thru them soon.
CB

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I tend to not care about cost of running lamps, I can't understand why people want to skimp on electricity to grow plants, and that seems to be a common thought around here. I try to grow the best plants, not just grow plants with the lest energy input.

HTH

I found this on another site. This is what I was talking about.


The only photoperiod manipulation from years of experiments that offered discernible improvements was the following photoperiod adjustment made for 1 or 2 calendar weeks at the point of maximum flowering rate: Daylength of 21 hours, 36 minutes with a dark period of 12 hours. To accomplish this, you need a 7 day, 24 hour digital timer. During a 7 day calendar week on Earth, the "sun" only cycles 5 times. This permits easily switching back to the regular 12/12 at your discretion. You may want to only alter during peak flower production to stimulate the plant's metabolism. Using this photoperiod throughout the flowering cycle will cause this:

A variety that takes 49 days of 12/12 to mature, won't see 49 - 12 hour dark periods under 21:36/12 until almost 10 calendar weeks have passed.

The total increase in light energy is almost 80%, which will produce larger yields, if all of your other enviromental conditions are kept optimal.

The total increase in flowering period is only 40%, half the potential room for improvement. This means you don't have to be perfect to win out.

Selective application of the 21:36/12 photperiod for only 1 or 2 weeks extends the wait only 2 to 4 Earth days, which makes up the missing 2 complete day and night cycles each week on Planet Ito. This permits the additional light energy to be provided without purchasing additional equipment or overloading existing circuits, which maximizes the existing system's capabilities. The main advantage is that matched with co2 and optimal nutrition, the plants metabolism will increase dramatically. I have only successfully tested this photoperiod for two weeks. The potential for a net increase of 40% over the entire cycle (80% increase in light energy vs. 40% longer wait) is worthwhile. Don't be afraid!

Day 1 - Sunday, 6:00am til Monday, 3:36am
Day 2 - Monday, 3:36pm til Tuesday, 1:12pm
Day 3 - Wednesday, 1:12am til Wednesday, 10:48pm
Day 4 - Thursday, 10:48am til Friday 8:24am
Day 5 - Friday, 8:24pm til Saturday 6:00pm

/bump
hey, just wondering how much different it would be the results from 6/12 to 7/12.
im currently considering between an w.c exhauster(getting 30-35ºC) and a digital timer(to put it 7/12)

Terramoto said:

hey, just wondering how much different it would be the results from 6/12 to 7/12.

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ah... The EXACT ANSWER is 1/6 better divided by 60 additional hours spent in flower (based on a 60 day strain). What the fuck kind of question is that?



Plants need photons; less input = less output.

I always wondered what it would be like to mimic the natural cycle of outdoors. Instead of using the typical 12/12 use a 14/10 cycle. I think plants would yield more due to more light hours, plus they would flower at the same rate as 12/12. Some Sativas may not flower under 10 hours but most Indicas and Indica hybrids should. I haven't tried it yet but one day I might do an experiment and see what cycle yields more. Say a plant takes 60 days to mature and you give it the 14/10 cycle. The plants are getting 120 more hours of light which in my opinion should increase yield.

Closet Funk said:

I always wondered what it would be like to mimic the natural cycle of outdoors. Instead of using the typical 12/12 use a 14/10 cycle. I think plants would yield more due to more light hours, plus they would flower at the same rate as 12/12. Some Sativas may not flower under 10 hours but most Indicas and Indica hybrids should. I haven't tried it yet but one day I might do an experiment and see what cycle yields more. Say a plant takes 60 days to mature and you give it the 14/10 cycle. The plants are getting 120 more hours of light which in my opinion should increase yield.

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I would think that each plant requires a slightly different "dark time" to initiate and to continue flowering.

I would also think that keeping the dark time right at that minimum and giving it as much light as possible, would give the best results. If the plant will flower/keep flowering at 15/9, that should (by my reasoning) give better results than 12/12. I'd guess 12/12 is used because it works on 99% of plants and it's easy to set/remember.

Blckbrd said:

I have been running this time period for about 7 or 8 grows of White Widow, bubblegum, blueberry, and now doing LSD, Lemon Skunk, and Master Kush. ChemDog/SourDiesel is on deck, and I hope to have Tom Hill's Haze right there with them on the next venture.

I don't do it for electricity - committed to the best grows I can do, I am more than willing to pay the bill. Not trying to skimp anywhere. I have always used 1000w mh for veg (24/7 - no sleep period at all) and 1000w Hps for flower. It's a dual ballast so i just switch bulbs. Just tried a 1000w dual spectrum that I am runnning now for the first time. Switched it about 20 days into flowering - just trying something new. So far so good, though I don't see any real difference in the development.

I have never really accurately compared/weighed yeilds, but from careful observation over the many months of tending, I am convinced that there is no less weight in the shorter cycle. I veg the plants to the size I want - usually pretty big. Then I flower them on the 7/12 and the product is as good quality and weight-wise as when running the 12/12.

I really do it to just speed up the harvest time. I like genetics that take 70+ days to flower and the 7/12 cycle is about 24% less time ( over two weeks less ) of flowering time. The finished product is huge, dense, and true to the genetic expectation. I have not observed any detriment at all. I suppose a theory could be that with more light energy, the flowers could be bigger, but that's hard to believe. I typically have to tie them to the ceiling to keep the bud-laden branches from breaking or tipping the resevoirs.

All in all, having grown both 12/12 and 7/12 exactly the same otherwise, it is my impression that 7/12 saves time without compromising anything. The plant is "tricked" into shorter day/night cycles.

I can't recall where the heck I was informed that 7 hrs is really as short as you should go, but it is a notion I have adhered to.

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What kind of yields were you averaging over those 7-8 harvestts with 7/12 off the 1000hps?

secondtry said:

The info about 6 hours of darkness has to do with far-red lighting and Pf/Pfr (ie. phytochrome). It's not proven for cannabis and IMO is not worth pursuing at all, 12-14 hours of darkness per night is good.

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Yes it is known that MJ flowers when it has a min of 10, preferably 12hrs of darkness, it is not the light period that stimulates flowering, but the night length, BUT it is possible to shorten the dark period where Pfr reverts to Pf by giving it a short burst of far-red (IR) light just after lights out, this will ruffly halfen the time it would naturaly take! im running this 12/6 cycle and will post results, i also plan on using this method after 28 days of 12/6 http://cannabis.com/growing/lighting-How_do_i_manipulate_the_photoperiod_for_larger_yields.html

blueberrydrumz said:

Yes it is known that MJ flowers when it has a min of 10, preferably 12hrs of darkness, it is not the light period that stimulates flowering, but the night length, BUT it is possible to shorten the dark period where Pfr reverts to Pf by giving it a short burst of far-red (IR) light just after lights out, this will ruffly halfen the time it would naturaly take! im running this 12/6 cycle and will post results, i also plan on using this method after 28 days of 12/6 http://cannabis.com/growing/lighting-How_do_i_manipulate_the_photoperiod_for_larger_yields.html

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I still havent gotten a reply from the manufactorer of the IR bulbs i purchased about exact nm readings, i suspect them not to be in the range of far red so ive decided after reading this & other threads to switch to 7/11 (Blckbrd got me thinking) Im not sure why Blckbrd isnt using 6/12, ive only flipped them 4 days ago so things should be ok... @ Blckbrd, PM me pls, be good to get some infos... i cant mssg you for some reason... thx

Hey blueberrydrumz, I'm interested to hear about your result with the 7/11 day/night cycle, can you tell us the conclusions? Thanks

Hello Blckbrd, I hope you are still around being this is such an old post. I am trying your system but I don't know what timer you are using. I can only find timers that are on 24 hr clock time which does'nt work because the on/off times are always changing. So if you could please tell me the name of the timer as its driving me crazy lol.
Thank you for your time
Str8shtr

Hello again, I am new on the site and dont know if i am sending this privately or not but if you could reply in any way private or not would be greatly appreciated. I am confused on the timer. Im using the 24hr digital set at 7am on 2pm off then 2:01am on and 6:59 off then it repeats. I have know ideal if this is right or not but I can't think of any thing else to do. I would REALLY appreciate your help especially if this is going to hurt me.

Thank You
STR8SHTR