Photoperiods and the flip to 12/12 . . . or could it be 13/11?

Just an “I’m curious question”:

I was always told that to initiate flowering a photoperiod cannabis plant requires 12 hours of uninterrupted darkness. During the late 70’s and into the 80’s I grew outdoors and plants were always in flower by September but the days were still about 13 hours long, almost the end of September before the nights are 12 hours long.

Is it actually the slowly increasing dark period that initiates flower or what? I know we use a 12/12 light cycle to initiate flowering in photoperiods, but outdoor plants seemed to flip before the nights reach a full 12 hours.

I’ve taken to setting my veg lighting to 14/10. I will put my outdoor plants in the ground late June…


IMHO natural sunlight in motion is wildly different than artificial lighting that remains in place. There are channels of communication in nature that we can’t replicate. Plants in nature don’t get total uninterrupted darkness. A crescent moon on a clear night is brighter by far than an LED indicator. When we force the plant to flip by going 12/12 it is like a really second rate interpreter using crude basic commands.


Remember that outdoor lighting provided by our nearby star does some interesting things in early fall.
As the sun strikes the earth in a greater angle the light rays at the beginning and end of the day is at a greater angle. What this does is provided more red photons due to the bending of the light rays. Some people use an effect that wakes the plants up in the morning and put them to sleep in the evening.
Simple by adding Red/far Red 15 minutes before sunrise/sunset and extending another 15 minute after sunrise/sunset. Will allow you to add additional 30 mins to 1 hour to your day light cycle.


Thanks for the information. I was reading some topic or the other about putting plants outside in the Spring and it got my curious up. I’m not thinking about playing with my light cycles . . .


I’d want to caution you about bringing your plant inside after being outside. I tried to bring plants inside and had troubles with bugs. Make sure you account for them if you choose to bring them back inside.