Wondering about switch to flower 12/12

Just curious about the switch to 12/12. I live in northern Ontario (Canada) and have grown outdoors and indoors. Indoors we just switch the lights from 18/6 to 12/12 to initiate flowering but outdoors, after June 21st (longest day of year), the length of daylight starts to dwindle each day.

Would there be any benefit (on a cellular or other level) to gradually shorten the indoor lighting from 18 to 12 hours over lets say 2 weeks?

Just a thought


Not really. Pretty much all hybrids have been developed indoors and under artificial light with a schedule similar to what you posted, and in fact may have kind of bred, intentionally or not, to perform under such an artificial light schedule.

Also, the way the photoreceptors work in plants, it is very “mechanical”, not including harding off younger less developed plants to light with greater intensity, there really is no need for a gradual change in photoperiod, nor the need for a gradual increase or decrease in intensity replicating sunrise or sunset.

In indoor growing, you would not notice any real benefit, and you would notice a decrease in plant production, maybe not as severe as running underpowered lights for the entire photo period duration, but nonetheless, less light to stimulate photosynthesis directly equals less sugars for the plant to produce vegetative growth and THC.

Happy growing,



Agree with MacGyver above. Basically no point. Toss em in and switch to 12/12. I go straight from 24 hr into 12/12. Works fine. Don’t think there’s any major benefit to reducing to 18/6 first…IMO. People do it and that’s fine. Just don’t think it matters much.



Do you feel that you see faster growth under 24/0 then 18/6?


I havent tried 24/0. I think its beneficial that the plants get some darkness everyday. There are some processes that happen in the dark.

The only time (and maybe its not correct to do so) I went 24/0 was the first few days for new clones.

In my original post I was only wondering if it might have some benefits to gradually switching to flower. In other words, 18hrs of light for a few days, then 17, then 16 until you reach 12/12.

I have always switched from 18/6 to 12/12 at once and just thought a gradual switch would mimick nature a little more. Never actually tried it.


I can tell you that I have gradually reduced the light from 18/6 to 12/12 over the course of one or two weeks in at least three grows now. I use this technique to better control the stretch - it seems to limit it some, but I do think that is somewhat perception and not reality. In any case, I haven’t, IMHO, gotten better or worse yields doing it… but when doing a SCROG it has helped me better plan and train the plant to incorporate a gradual reduction in lighting. I believe @myfriendis410 has done this as well.

My question re: 24/0 or 18/6 was directed at @thewidowwhite.


Yeah; I saw NO reduction in stretch the last time I did it. But it may be somewhat strain dependent too.


If you really want to emulate sunset, you need to add far red and IR at “sunset”, lol.

But seriously, it isn’t necessary. Just go straight to 12/12.


I find you get shortest veg time with a 20 hr light cycle. Plants get tired with less than 4 hrs a day sleep time. Also roots grow faster in the dark