What is the least amount of dark hours to keep 99% of plants in flower?

ShroomDr · Sep 26, 2010

Most growers read 12/12 and assume plants need 12 hours of darkness, and this simply is not the case. 12/12 is a convenience. Some people grow 21:30 on / 12 off, (I think thats right. Its suppose to mimic 5 dark periods per 7 earth days) or 9:30 on / 12 off (9 dark periods). Both of these exploit the day period, im interested in the dark period.

At one time, I was growing 13 hours on, 11 off, thinking the extra hour of light would give the plants more energy (1/12 more). Now i am forced to flip flop this particular circuit. I have two tents with vertical cool tubes, each one on a timer set for 11:45 of HID lighting, to make sure both lighting systems wont be on at the same time.

Due to the vertical lighting, i am forced to do the garden maintenance when the lights are off. Rather than losing out on valuable photosynthesis time and falling back on my knowledge of 11 hours of darkness being perfectly acceptable, after the light goes out, i open the tent (basically right away).

Long story short, I have spent over 2 hours with the tent open (tent lights off, room lights on), giving them less than 11 hours of darkness countless times. Sometimes they get the full 12:15, sometimes its 11, sometimes its down to 10, without ill effect. Ive been doing this for 3-4 months, perpetually growing 6 strains, 7 phenos, no problems.

I probably wouldnt push it much further, but i'd love to know if others have. What's the shortest dark period needed to force and keep 99% of strains in flower? I want to say its close to 9 a little more.

-

VerdantGreen · Sep 26, 2010

it would be strain dependent.

but also giving them a shorter night even every other day would be different to doing it every day, and the speed of flowering and ripening might change.

the best way to do it is sposed to be to retain the 12 hours dark but give a longer day of 14-16 hours. day length matters much less than night length to make them flower.

VG

DocLeaf · Sep 26, 2010

^^ wat VG said.

12hours.

ShroomDr · Sep 26, 2010

VerdantGreen said:
it would be strain dependent.

but also giving them a shorter night even every other day would be different to doing it every day, and the speed of flowering and ripening might change.

the best way to do it is sposed to be to retain the 12 hours dark but give a longer day of 14-16 hours. day length matters much less than night length to make them flower.

VG

might and suppose are conjecture, im looking for hard evidence.

DocLeaf said:
^^ wat VG said.

12hours.

ive already demonstrated you dont need 12 hours. 12 hours is incorrect.

VerdantGreen · Sep 26, 2010

indeed some strains will start to flower under more than 12 hours dark, but you missed my point - that its better to have a longer day of over 12 hours but keep the night period at 12 hours.

for shorter nights the only way to find out exactly what you could get away with would be to experiment with each indivdual pheno of each individual strain, good luck with that.

and as i said, you may be able to get it to start flowering in say 10 or 11 hours of darkness, but it may also make it take 2 weeks longer to ripen. sorry i cant give you 'hard evidence' im just trying to help by telling you what i know and what i think may happen, based on a reasonable knowledge of how auxins work and observing how plants grown outside will accelerate their flowering as the nights get progressively longer.

VG

ShroomDr · Sep 26, 2010

VerdantGreen said:
indeed some strains will start to flower under more than 12 hours dark, but you missed my point

You have certainly missed my point, i have not mentioned 'more than 12 hours of dark'.

To the best of my knowledge, marijuana needs a certain amount of darkness to build up enough flower hormones. Most people think this is 12 hours, and it obviously is not. Its not 11 hours, based on my own indoor observations, and the shortened dark period has no effect on ripening time. (Ive been running a couple of my current phenos for years).

'observing how plants grown outside' is a very poor analogy IMHO. You can't control the dark period. It becomes 'the chicken or the egg' when attempting to correlated outdoor ripening and longer dark periods. Even the best example of an 8 week flowering plant vegged indoors under 24/0, and placed outdoors 8 weeks before vernal equinox would not be a good analogy, as the sun continues to build intensity as the earth tilts (something not happening indoors).

But i digress, Im not interested in longer dark periods, only the shortest possible dark period to build up the flowering hormones. Im not trying to get into an argument, just some useful discourse, as that is what is most helpful to all readers. :ying:

I want to know the least amount of dark period hours other users have used, and if they have pushed it too far.

hempluvr · Sep 26, 2010

ShroomDr said:
You have certainly missed my point, i have not mentioned 'more than 12 hours of dark'.

To the best of my knowledge, marijuana needs a certain amount of darkness to build up enough flower hormones. Most people think this is 12 hours, and it obviously is not. Its not 11 hours, based on my own indoor observations, and the shortened dark period has no effect on ripening time. (Ive been running a couple of my current phenos for years).

'observing how plants grown outside' is a very poor analogy IMHO. You can't control the dark period. It becomes 'the chicken or the egg' when attempting to correlated outdoor ripening and longer dark periods. Even the best example of an 8 week flowering plant vegged indoors under 24/0, and placed outdoors 8 weeks before vernal equinox would not be a good analogy, as the sun continues to build intensity as the earth tilts (something not happening indoors).

But i digress, Im not interested in longer dark periods, only the shortest possible dark period to build up the flowering hormones. Im not trying to get into an argument, just some useful discourse, as that is what is most helpful to all readers.

VG answered it right. It is strain dependent. 12/12 is widely accepted because most all strains will flower indoors under 12hrs of darkness 12 hrs of light. However if 12 hr days were needed to flower then outdoor strains would not flower until late in the year. For instance White Widow will flower with 15 hrs of light and 9 hrs of darkness. With 12 hrs of light she finishes nicely but with 15 hrs of light she has more weight and better crystal production..IME!

At the same time. Some strains vegged under 24 hrs of light will start to flower if dropped to 18/6. Based on the fact the days have been very long and never ending so a cut to 18/6 or 17/7 may cause it to flower. After all the days are shorter. I had this exact thing happen with a bagseed sativa I had in 2008. I vegged for 24 hrs for 2 months then decided to cut back to 18/6 and everything in the veg room stayed in veg except the one plant which began to flower. Just my :2cents:

I think u are right tho...9 hrs of darkness would work nicely with most 8-9 weekers!

STUPPA · Nov 24, 2010

I think the amount of dark needed to maintain flowering might be different to the amount needed to induce it .What i mean is it might require more dark time to start the flowering response than it would to maintain it in later flowering .
Plants might not start flowering with 9 hours of dark period but later in bloom 9 hours dark might be sufficient to maintain flowering, not saying it is tho LOL .

you would have to do a painstaking experiment involving gradually increasing the dark period a half hour at a time and then leaving it at that length for 2 weeks ,then if no flowering occured you would have to do it all over again. That still would'nt give you an accurate figure tho cos you have to take into account the gradual build up of flowering hormones and how long these hormones can remain active.

zenoonez · Nov 24, 2010

Clones + cfls + cheapo timers = win

*mistress* · Nov 24, 2010

around 8-9hrs.....

very simple:

reduce light by :30 min, every 48hrs....
from 24/0, to around 15/9.... 9hrs dark generally initiates reproductive organs....

though each specific cultivar will have its own unique flower/fruiting trigger, 9- 9 1/2 hrs dark generally triggers & maintains flowering.....

TruthOrLie · Nov 24, 2010

I remember reading a thread here where a guy shortened light period to 7-8hrs and kept dark period at 12hrs in order to get more dark periods a week.

The thought behind this was that although plants photosynthesize for 12 hrs, the degree to which they do so greatly diminishes after 6-7hrs.

So really you only need 6-7hrs of light, then you can go work on your vertical garden without worrying about having much of an impact on your photosynthesis period.

*mistress* · Nov 24, 2010

yes, kind of like member heath robinson does w/ relays.... or only using 1/2 of the available light during the "lights on" period....

plants seem to require a period of a week or so to adjust to "shade" conditions.... or, less light... try it w/ veg. they adapt to low light conditions, & will eventually grow the same.

example:
veg under 2x 400w lites. turn 1 off @ 6 hours, for 1 week. during 1st few days, there may be almost no growth. after that, if conditions kept constant, they will grow same as w/ 2 4oo's.... :2cents:

it seems more of the constant conditions than lack of lite. they require adjustment, maybe.

angles of lite seem to affect growth, too.

can also do 16/12 cycle, to maximize light during flowering....

a week contains 168 total hrs....

or,

16/12
+
16/12
+
16/12
+
16/12
+
16/12
+
16/12
=
96 lite / 72 dark
=

168 total / 6 "days"

standard 12/12
=
84 lite / 84 dark (7 "days")

ShroomDr · Nov 24, 2010

STUPPA said:
I think the amount of dark needed to maintain flowering might be different to the amount needed to induce it .

I could see this being true, but its worth pointing out i run perpetual, putting new plants into flower at least every two weeks. Ive never noticed a delay. Along the same type of line, i could see maybe a few nights in a row of 7-8 hour dark periods may not mess up the plants in deep flower, but would inhibit a plant from being able to 'kick start' into flowering.

*mistress* said:
around 8-9hrs.....

Have you tried this or is it just speculation? Ive done 9.5 hours of darkness a few times, but i try to keep at least 10. Frankly i dont want to be the one who says 'o shit i fucked up my crop, but i figured out the answer to my question'.

FWIW when i have to be in the garden longer than 2 hours, i will just delay the turning on of the light, making sure they get 10 hours of darkness. (So if lights normally go out at 12am, and im working with the tent open until 4am, i'll unplug the ballast from the timer, and wont plug it back in until 2pm.) Again, no noticeable harm/effect.

ShroomDr · Nov 24, 2010

TruthOrLie said:
I remember reading a thread here where a guy shortened light period to 7-8hrs and kept dark period at 12hrs in order to get more dark periods a week.

something along the lines of 6:30 on/12off, will give you 9 dark periods/week. You could also go the other way and go 21:30on/12off and have 5 dark periods per week.

I believe the plants mature by the number of dark periods, so 9 dark periods a week will get you to harvest sooner (with less photosynthesis) and 5 dark periods a week will get you there slower (with a lot more photosynthesis). Again, they didnt need the full 12 hours of darkness, that was just the examples ive seen.

STUPPA · Nov 24, 2010

*mistress* said:
yes, kind of like member heath robinson does w/ relays.... or only using 1/2 of the available light during the "lights on" period....

plants seem to require a period of a week or so to adjust to "shade" conditions.... or, less light... try it w/ veg. they adapt to low light conditions, & will eventually grow the same.

example:
veg under 2x 400w lites. turn 1 off @ 6 hours, for 1 week. during 1st few days, there may be almost no growth. after that, if conditions kept constant, they will grow same as w/ 2 4oo's....

it seems more of the constant conditions than lack of lite. they require adjustment, maybe.

angles of lite seem to affect growth, too.

can also do 16/12 cycle, to maximize light during flowering....

a week contains 168 total hrs....

or,

16/12
+
16/12
+
16/12
+
16/12
+
16/12
+
16/12
=
96 lite / 72 dark
=

168 total / 6 "days"

standard 12/12
=
84 lite / 84 dark (7 "days")

So why not go 24/12 ,then you'd get twice the amount of light in one "week" surely that would'nt work .

*mistress* · Nov 24, 2010

..................

*mistress* · Nov 24, 2010

STUPPA said:
So why not go 24/12 ,then you'd get twice the amount of light in one "week" surely that would'nt work .

it may work.......

there are already "auto-flower"-type plants......

c3 & c4 plants are extremely adaptive.

if a gardener set out to breed, or even make a specific generic plant adapt to those conditions, it may be possible.... consistency of the lite regime seems key.

the 16/12 regime is not new. there was a thread on that @ og, or cw.... & there is an old one, here, @ icmag:

18/12 light cycle

& the #'s:

standard 12/12
in 56 day/night 24hr periods:
7x24=168 total hrs per week
1x12=12hrs light per day
1x12=12hrs dark per day
7x12=84hrs light/dark per week
8x84=672hrs of light per 8 wk cycle
8x84=672hrs of dark per 8 wk cycle

16/12 cycle
6x(16/12)=168hrs per week
6x16=96hrs of light per 7 day calendar week
6x12=72hrs of dark per 7 day calendar week
96+72=168
8x96=768hrs of light per 8 week cycle
8x72=576hrs of dark per 8 week cycle

768-672=96 more hrs of light over an 8 wk period w/ 16/12
672-576=96 less hrs of dark over an 8 week period w/ 16/12

the standard 12 hr dark period is followed throughout w/ 16/12

12/16
how about 12 hrs of light w/ 16 hrs of dark? this will give:
6x12=72hrs of light per 168hr week
6x16=96hrs of dark per 168hr week

or

6x12x8=576hrs of light per 8 week bloom cycle
6x16x8=768hrs of dark per 8 week bloom cycle

768-672=96 more hours of dark per 8 week cycle w/ 12/16 than standard 12/12
768-576=192 more hours of dark than 16/12

hope this helps

TruthOrLie · Nov 24, 2010

I guess you guys missed the part where I said photosynthesis dramatically decreases after 6hrs.

Why would you go 21 hrs? That's 15hrs of dramatically decreased photosynthesis with no time for the plant to cycle the sugars during dark period.

ShroomDr · Nov 24, 2010

TruthOrLie said:
I guess you guys missed the part where I said photosynthesis dramatically decreases after 6hrs.

By that logic, the ideal way of doing things would be 6on/10off. Ive certainly never seen anyone advocating that. (Not that it wouldnt work, just havent seen it.)

Its certainly an interesting topic, worthy of its own thread, i would prefer this thread stay on topic with discussions about the least amount of darkness needed.

*mistress* said:
the plant notices even a few minutes of lite difference. that is the raw material used for their food production. similar to animals feeding times.....

This certainly is the exact opposite of the my observations. Further more, i think what your saying would be impossible to prove. How do they notice, and to what effect?
A plants raw materials are also nutrients, are you claiming that if a plant is fed every other day and then a day is skipped, the plant notices? Again IMHO this is unobservable and a ludicrous statement.

In my tents i am currently running 9 different cuttings (20 plants, 5 strains), with no observable effect from the dark cycles i have been talking about.

junior_grower · Nov 24, 2010

TruthOrLie said:
I guess you guys missed the part where I said photosynthesis dramatically decreases after 6hrs.

Why would you go 21 hrs? That's 15hrs of dramatically decreased photosynthesis with no time for the plant to cycle the sugars during dark period.

these porcess don't occur in the dark they are light independant, just don't need light to occue. They in fact happen all day along as does photosythesis for about 10mins after lights out.

What is the least amount of dark hours to keep 99% of plants in flower?

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