What is the least amount of daylight a plant can get and still veg?

Ok, so I want to know when the earliest is that I can safely plant out my weed in a greenhouse? Assuming 12/12 is the general indoor light schedule to flower a plant, what is the least amount of natural daylight that a plant can recieve and not trigger flowering? Or put another way, what is the most amount of darkness per day before flowering is induced?

It depends a lot on the strain. Some tropical strains might flower with more hours of light than some harty indicas from more temperate regions that…maybe I have that backwards…but you get the point. You could add light to keep them thinking it’s daylight longer, or earlier, or get creative and do both? Anyway, it wouldn’t need to be grow light intensity, just enough that it ‘looks’ like daytime to the plants.


But will 12 and 1/2 hours trigger? 13 hours ? Obviously its more the hours of darkness that really matters but for sake of arguement… lets use daylight hours.

I believe that’s true…it’s a hormone that is triggered after so many hours of darkness, which is why some people put their plants in the dark for 48 hours before flipping, just to really drive it home, “flower, yo.” I think the magic number is as low as around 10 hours of darkness for some strains, closer to a full 12 for others (probably the more tropical ones with a longer growing season).

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So in your opinion, and anyone else that may have one, lets say you have had your starter plants on the back burner sucking up 18/6 glorious hours of non cloudy LED daylight for 2 months and now you want to set them free in April in the greenhouse. April 01 sees 13 hours of daylight, April 15 sees 13.5 hours April 25 sees 14 hours . How to reduce the light in the grow room to prepare the plants for the reduced light without triggering flowering? Or will it even matter? I want these plants to be monsters! A full 12 foot high greenhouse and I want them banging on the roof!

Take my opinion as one with no outdoor experience, only formed from reading and seeing others’ experiences. That said, if it were me, I’d set up the cheapest shop light I could find on a timer to run from just before dusk until midnight or whatever would equate to your indoor schedule, total hours of lights on time. That should be enough to prevent them from flowering. As always, I don’t quote anything as the gospel. There are many ways to skin a cat.

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Might be the answer?! Perhaps Im forced to wait till May? But yep that could be the ticket.

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That might be your safest bet. Revegging wouldn’t be ideal.


Or you can add a light in the greenhouse and have it come on just at dusk, just enough to keep it from flowering.

I know you’re asking about scotoperiod-sensitive cultivars, but I’m going to point out that scotoperiod-insensitive cultivars (commonly known as “autoflowers”) might be what you’re looking for, and let you get an early greenhouse crop before the day length hits 14 hours (the minimum I’d give, to be on the safe side).

If I’m remembering my reading correctly, cannabis needs a minimum of 10 hours of sunlight, but that has to be a rough estimate with variance due to shading, altitude, and latitude.

I feel like 11 hours of dark is the most I’d give a plant in vegetative growth, unless I was stress-testing.

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Yes and no on the scotoperiod plants. All will be Afgjani and Himalayan. They have the capacity to hit 4 meters but more than likely 3 could expected? Thats still 10 feet in American. Id like a full 12 cuz thats how much height I have. I may need to supply heat toward the end? They suggest end of November early October finish. October is getting late here but it should be doable.

I think I had a 14/10 cycle with my GSC Beast and she in Veg mode for 3 months. She managed to flower after 3 months. I did finally correct the light schedule to 12/-2z

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I may have to wean my indoor off 18/6 down to 14/10 and then wait till I get 14 daylight outdoors. Makes more sense than broadcasting to the neighborhood that my grow is on! Not that most give a crap but there is always a thief in the woods!


I’ve done quite a bit of outdoor growing. In general, my plants outdoors begin flowering when daylight hours drop to 14. Of course it’s not just the number of hours, but the reduction from what they were used to. Some strains, like Ilgm Cali dream, begin flowering even earlier (I had them begin flowering at the end of July last year).

Taking plants from an 18/6 indoor light schedule and putting them outside under 14/10 will more than likely have an impact. They may not go into full flowering since daylight hours are increasing, but it’ll definitely confuse them for a bit.

Adding a light, as mentioned above, to keep them illuminated, is a solid idea. It doesn’t need to be intense. Just enough to make them feel like it’s still light out.