I've heard that there are some advantages to giving the plants 24-36 hours of total darkness before commencing the 12/12 cycle? Anyone care to support or rebuke this theory? Plan on starting flowering after the lights go off tonight so I'm wondering what's the best way to do this here.
I personally have seen no benefit to this theory with my grows. I just switch to 12/12 when it's time to flower.
The idea is that the plant is responding to the length of the dark period (generally you need at least 12 hours uninterrupted dark), so to "jump-start" the hormonal reaction to flower you start the flower period with an extended dark period. It seems to make some sense but I honestly don't know if scientifically it is true. There is a second possible reason to extend the dark period at the start of flowering, a purely practical one -- to get the flower light cycle on the time you want. For example, I usually use 18/6 veg lighting to control heat (lights are out 12p-6p, the hottest part of the day). For flower I will want dark to be about 8am-8pm. So my options are for the first day to go lights out at 12p and then not back on until 8p (end of one cycle then start of the other), but that would give me only 8 hours of dark. Or, I could end veg with lights out at 12p and then start flower with lights on 8p the next day, for 32 hours of extended dark. I have done it both ways and not seen much difference in how soon or robustly flowering starts.
It was an idea that I saw in the grow bible so I thought I'd throw it out there and see what everyone thought. I'm gonna see if I get any more replies from someone who's tried it.