The great schedule debate 24/0 or 18/6

Ok so here it is, up until recently I thought it didn't matter and was more to preference how you veg, recently I have seen many good arguments for 18/6 but noticed people here like 24/0 better. So I spent the last two days googling if plants need darkness and 8 out of 10 answers came from pot forums :hubba:

Then I hit up wiki and here is what they say
"Light can be natural (outdoor growing) or artificial (indoor growing).
Under artificial light, the plant typically remains under a regime of 16–20 hours of light and 4–8 hours of darkness from the germination until flowering, although the plant can use a full 24 hours of light without harm. There is an ongoing debate over the importance of the "dark period". It has been shown that, when subjected to a regimen of constant light without a dark period, most types of flora, including Cannabis, will begin to show signs of decreased photosynthetic response, lack of vigor, and an overall decrease in vascular development. There is no defined flowering "stage", unless you are discussing an auto-flowering variety (Cannabis Ruderalis). Typically, flowering is induced by changing the light schedule to 12/12, or 12 hours of light and 12 hours of darkness. Flowering in cannabis is triggered by a hormonal reaction within the plant that is initiated by an increase in its dark cycle, i.e. the plant needs sufficient prolonged darkness for calyx development (flowering) to begin. Some Indica varieties require as little as 8 hours of dark to begin flowering, whereas some Sativa varieties require up to 13 hours."


So basically I read this as its better to give some dark verses than no dark. I would like to hear from everyone on their thoughts of what wiki has to say.
I also think of it this way, plants are living "creatures" and as far as I know all living creatures need sleep. Kind of an over simplification but I think it applies.

multifarious said:

24/7 365 all day every day, my T5s never get switched off

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:yeahthat:

There is absolutely no debate for me and never will be, I have seen first hand how much better 24/0 is over 18/6. MJ needs no dark period. Only time I would ever use anything other than 24/0 is if I was dumb enough to try and grow through one of my Summers and needed to try and keep temps down during the hottest part of the day.

I agree with all the above. I used to think it needed a "rest" but found I was wrong.

I root clones under four 40w fluro tubes (grow) from home depot. On 24 hrs. With Co2. Just popped roots in 5 days. My new record.

Then they go under four 1000w MH, in the same room so they also have Co2. Hoods 3' or 4' off the tops at first. Dropping 6" per day until close. I pinch the tops at about 10" tall to slow them down and bush them out.

I don't notice any slowing in the 3 or 4 weeks they are under 24 hour lite. In fact they seem to grow faster the longer they are in there. Around 2" per day when I switch to flowering. I would call that rapid growth.

First of all, I never trust Wiki. Anyone can write anything they want without any citations. Most of it is just opinion.

Marijuana does not need a dark period and will grow all the time the lights are on. I have never seen any kind of scientific study that suggests that a 24 hours light schedule will cause "decreased photosynthetic response, lack of vigor, and an overall decrease in vascular development." I also have never seen it in real life.

I have done it both ways and found that my plants grown under 18/6 stretched more and reached for the lights more than those vegged under 24/0. My Bro did the same thing and got the same results. I think people who grow under 18/6 get confused by the "rapid growth" that they see in their plants. They are thinking that the plants are growing faster, but the truth is the plants aren't "growing", they are "stretching". The difference is internode length. 24/0 plants that are 12" tall with 12 leaf nodes is more "growth" than the 18/6 plants that are 16" tall and only have 8 leaf nodes.

multifarious said:

24/7 365 all day every day, my T5s never get switched off

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:yeahthat:

once i was convinced to go 24-0 i never looked back, there is absolutely no reason to use 18-6 except maybe one.... if heat is an issue in the summer maybe you would wanna go dark during the peak heat hours, but thats it.

To add more to this debate, what about if using MH instead of T5/T8. The 24 hours schedule with T5's makes up for a lot of the lumen difference. So what about with mh? do you still run 24hr?

24/7 under any light,give'm all they can take,just like nutes.

WrEkkED said:

To add more to this debate, what about if using MH instead of T5/T8. The 24 hours schedule with T5's makes up for a lot of the lumen difference. So what about with mh? do you still run 24hr?

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I would use a 24/0 schedule regardless of the type of light source, provided I could keep temps in check. When I used to use HPS for veg I ran a 24/0.
Just makes too much sense to not. Jmo

WrEkkED said:

To add more to this debate, what about if using MH instead of T5/T8. The 24 hours schedule with T5's makes up for a lot of the lumen difference. So what about with mh? do you still run 24hr?

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The amount of lumens really has nothing to do with it. It is when they are in the dark that the stretching happens.

When I ran a 400W MH, I ran it 24/7. When I run 216W of T5, I run 24/7. I never noticed any difference in veggy growth with the extra lumens from the MH, just more electrical usage and more heat. I believe that the difference in lumens is offset by the fact that the T5s spread the light so much better and you can keep the lights right on top of the plants.

The Hemp Goddess said:

Marijuana does not need a dark period and will grow all the time the lights are on. I have never seen any kind of scientific study that suggests that a 24 hours light schedule will cause "decreased photosynthetic response, lack of vigor, and an overall decrease in vascular development." I also have never seen it in real life.

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This is the kind of stuff I looking to for, but what about the shock of being put into 12/12 then? Is there any evidence that a vegged 18/6 would make the transition better because it already has those hormones somewhat in it? Where as a 24/0 plant wouldn't have the hormones that are caused during dark period?


I also hope you all don't feel this topic has been beaten to death. Couldn't help it after hearing a few things that made sense and I wanted the opinion of my mentors, heros and maybe even my kin :icon_smile:

Not that I'm any pro or anything, but when I switched to 12/12 I took a week to do it. Went from 24/0 to 20/4 for 2 days then to 18/6 for 2 days then switched to 12/12 and seemed to go well.

I do agree that running 24/0 will not harm the plant at all. I veg my newly rooted clones under 24/0 with T5 lighting for 10-14 days.
I must say that once I transplant them into bigger pots and put them under the 1000w MH, I do run 18/6.
For me, it is more about electrical use then anything else.

I have never seem anything on any benefits of going to an 18/6 or slowly increasing the dark prior to flowering. I am thinking that your plant is probably simply going to stretch x number if inches when you put into flowering...regardless of how your transition to 12/12. It would be nice to know if there was some (cannabis) study on that.

ShecallshimThor said:

This is the kind of stuff I looking to for, but what about the shock of being put into 12/12 then? Is there any evidence that a vegged 18/6 would make the transition better because it already has those hormones somewhat in it? Where as a 24/0 plant wouldn't have the hormones that are caused during dark period?


I also hope you all don't feel this topic has been beaten to death. Couldn't help it after hearing a few things that made sense and I wanted the opinion of my mentors, heros and maybe even my kin :icon_smile:

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I have not seen any shock when putting plants in flower(12/12) after running under 24/0 ...Ive read that peeps cut the lights back...and some that dont...

:48:

i'll agree with most and say i don't forsee any problems arising from 24/0.
but i'll be the odd one here (only one?) and admit i use 18-6 for veg (actually more like 19 or 20 though )
saves me a bit of power, and my nodes are already closer than i need them.

i end up cutting most the lower branches off anyway. really don't gain anything having extremely tight nodes - at the very bottom of your plant. with typical stretch at the top.
*now if it stopped/slowed stretch post-flip, for sure. that's when i care about node tightness

The information you read is bogus. Up here in the north during the summer we have nearly 24 hours of sunlight and get world record sized produce. I have grown under 18/6 and 20/4 and 24/0. I actually have grown autos under 24/0 and had them finish a week earlier than the same strain at 20/4. Proof is in the pudding, and its dank pudding

Hamster Lewis said:

:yeahthat:

There is absolutely no debate for me and never will be, I have seen first hand how much better 24/0 is over 18/6. MJ needs no dark period. Only time I would ever use anything other than 24/0 is if I was dumb enough to try and grow through one of my Summers and needed to try and keep temps down during the hottest part of the day.

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:yeahthat: 24/7 while in Vegg.