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Light duration


New Member
Do the plants detect the length of time in the dark like they do hours of light? For instance, if the plant is running a 18/6 light cycle and it is left in the dark for 12 hours would that shock it into starting to flower?


Grow Journal of the Month: July 2020
it can. autos are notoriously sensitive to changes, loads of things can set them off, but they don't need light cycle to flower at all.

photos are more stable. if late in veg it can have an effect. normally it will take couple days of shortened light cycle to get a photo to turn.

mostly it comes down to the individual plant and strain.


Well-Known Member
People typically switch to 12/12 for flowering and leave it there until the harvest. Its a gradual transition.

Ive read somewhere on here that it is the length of darkness they respond to as opposed to amount of light. Perhaps somehow tied to photosynthesis?


420 Sponsor
If it is auto flower, it will flower no matter what lighting cycle you are using; But if it is normal strain, set the lighting cycle to 12/12, then it will begin flower. ;) :high-five:


Well-Known Member
Reproductive cycle depends on the species and/or sub-species.

Photoperiodism - Wikipedia

Photoperiodic Cannabis usually starts to show buds around 1-5 weeks after being introduced to equal night and day, depending on strain/phenotype.

Word of the day :thanks: for posting that link.
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