How soon can you flip to 12/12?

Ive been Googling this and the answers so far - as is so often the case with our hobby - are all over the place. I am having a hard time telling if there is any real science behind any of these answers or not, but I trust you guys more than other sites, so Im going to ask you guys for advice :slight_smile:

Some people claim you can go to 12/12 from seed.

Others say wait till after you see pairs of leaves, or three or four or five nodes etc.

Others say wait till you see pre-flowers.

Im having problems with my roots seriously outgrowing the space in the root chamber (HPA) after 5 weeks of veg, so I really need to start sooner than that. Im thinking two to at most 3 weeks is going to be it if I want to keep the roots happy and not crunched in or eating my spray nozzles.

I would like to hear from you guys about the pros and especially the cons of flipping early, and how early is truly safe and/or wont hurt final product too much.


I think there’s no benefit to switch until they are sexually mature ( preflowers and or alternating nodes) if starting from seed.
If they are clones they should be ready to go once established.
But that’s just like my opinion man✌️


From what I’ve been reading up it’s generally best to let a plant that has a male and female expression to fully express sex before flowering.

From what I have been able to understand it’s much better able to handle stress when it’s hormones are stable.

Feel free to ignore what I said though as I’m still learning myself. I do my best to retain what I do learn, but I make mistakes like everyone else. I’m bound to be far from the mark if I’m unsure about my information.


I did similar research and found so many claims and so much evidence that 12/12 from seed works, that I wouldn’t hesitate to try it. I haven’t yet, but I certainly will at some point.

For your purposes, go with your gut and do a 2 week veg and then flip.


It works and isn’t the worst way to pheno hunt in a bunch of 1 gallons…I personally don’t like it (my opinion means about zilch though so please take it with a grain of salt), and am in agreement with @OniTenshu about stress issues…it’s a fun endeavor and allows a different aspect of growing techniques to be learned, from a hobby stand point everyone should give it a try though just to say you did it once :smiley:


Imo photo period won’t start to flower until there ready to do so from any information I’v gathered on the subject when 12/12 from seed I guess it kinda depends on how big of a harvest you want, my two ladies I have going now I started 12/12 from seedling for two weeks then gradually raised it to 18/6 over the next weeks seemed to do fine maybe that’s why I was able to determine very early in what the sex was.


Clones will be ready in less time given that by the time you cut them they are prolly sexually mature. On the other hand, from seed they need a few internodes to start reaching mature age.


Running 12/12 usually gives you those single cola plants… It’s not gonna cut the time of a photo as it still has to be mature enough to flower, just drastically reduces height and side branching


Ya you can start 12/12 from seed or thereabouts, but you may not get a proper representation of the plants potential. I find plants always seem more vigorous, potent and yield better when I run then a second time from clone.


It’s recommended for long-flowering sativas in some cases to cut down on height issues. From what I understand, limited as it is, the plant will decide when it’s ready. The natural equatorial lighting is 12 hours year-round. Then to finish, cut the light down to 11 on…
Happy growing. :slight_smile:


i did 12/12 from seed once and it still took 8 weeks or more before i saw pistils … they won’t flower until they’re sexually mature i.e. preflowers


I’ll just repeat what’s been said here. A seedling will veg for three of four weeks even on a 12/12 cycle. Once they are mature (showing pre-flowers or alternating nodes), they will start to flower under 12/12. I know you aren’t planning to go 12/12 from seed though.

Starting to flower too young can cause hormonal stress as the flowering hormones build up. Like any stress, this can potentially lead to intersex traits. Generally I like to go four weeks from sprout then flip.


i have a few plants which i’ve been waiting for preflowers on, probably 4 weeks or more from sprout and they’re still in solo cups, then i have one thats prob over 8 weeks in a 1 or 2 L pot still hasn’t showed so i threw a bottom branch in to the flower tent in a cup of coco and its been 1-2 weeks and that hasnt done shit either yet!!

i had to cull 3 males from my flower tent and that’s pissing me off … i’m investing in a qPCR thermal cycler so i can do at-home sex testing of my plants … that’s it


Right, of course…the good old qPCR thermal cycler. Gotta have one of those!!

Seriously though, what the hell is a qPCR thermal cycler lol


I found whether 12/12 from start or not your plants are still gonna go through a veg cycle for that first 2.5-3weeks anyways before they think or even can consider flowering, and found it was more a benefit to just given them more light to start off with anyways.


hehehehehe You folks are sounding just like the folks I found when I Googled this - all over the place!

So, to sum up, flipping early may work just fine or maybe not :smiley:

It sounds like the worst case is hermie city from stress, and/or stunted growth, smaller colas, etc. Plus, it may not actually reduce he grow time at all.

So, I need to balance that against the roots outgrowing the available space well before harvest, and the stress and other issues from that situation…

My current grow is still a week or so away from harvest, so Im starting the seeds for the next grow in dixie cups now. That will give them at least a week or two head start while I clean and make changes to the HPA system.

I really should have started them last week or even earlier now that I think on it…

I guess I will just have to see how it goes. I will report back!!


quantitative polymerase chain reaction thermal cycler, it rapidly heats and cools a sample while spinning to separate and analyze the nucleic acids … in this application it looks for a Y chromosome to identify male samples


Im waaay too broke to get one of those. I just buy fem seeds :slight_smile:


I have a PCR I got from gov auction. I’ve wanted to start messing with it but I’m not sure where to buy chemicals without a business licence. Do you have any guides you’ve looked at?


actual qualitative/real-time PCR isn’t absolutely necessary, it’s possible to do standard PCR detection and you could build a DIY arduino one for under $85