24 hour light for germinating marijuana

A question from a fellow grower:

When germinating do I keave the lights on 24 hrs a days before planting outside?

I would not recommend that. 16-18 hours a day for regular seeds; 18-20 hours a day for auto- flowers. 15-18 for feminized seeds. depends on what you are growing.

I never advise anyone to grow anything 24/0. Plants are like human beings; They need the rest to acclimate and grow properly. :smiley:

Something to think about, all cannabis, indicas, sativas or ruderalis are all C3 plants, which is why we don’t supplement CO2 during the dark period, and this means they do not need a dark or rest period at all during the vegetative period. They just don’t need it and actually quite a bit of stretch can occur during the dark period or be stimulated by the dark period. So, not only can you get about 33% faster growth with 24/0 lighting (in contrast to a 16/8) during the vegetative growth period, you will notice tighter internodes as well.

Cannabis does not suck up and store CO2 overnight like C4 plants, however they do do some important biological processes even in the dark and I think darkness during veg still does have use in certain situations to help an ailing plant. As well as of course 12 hours needed for flowering in non-autoflowers or more darkness for finishing and trying to get some of the chlorophyll out at the very end. In the end, C3 plants normally do not need “rest” or darkness at all until the flowering period is to be started, and none at all, ever, for true autoflowering plants. Some sativa hybrid autoflowers may need some darkness to help them flower or finish, but otherwise, they just don’t need a dark period during veg.


It has been awhile since I’ve visited this topic, and I would like to add some clarification as this topic states specifically “germination”, and that although I still agree with what I’ve said here, when growing from seed, not from clone, an absence of a decent dark period can increase the chance of male plants or hermaphrodites, even from feminized seeds. And if growing from seed, I agree with Latewood and a 16-18 hour day is probably best.

Happy growing,


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