Photoperiod

The photoperiod is the daily duration of light and darkness to which a plant is exposed. For many plants, it is the crucial switch between growth and flowering. In indoor cultivation, the photoperiod allows for targeted control of the life cycle – which is why the term is central to cultivation.

How light controls the plant

Photoperiodic plants "read" the length of the dark phase to determine the current season. Many hours of light signal summer – the plant remains in the vegetative phase. A common rhythm for this is 18 hours of light and 6 hours of darkness (18/6). If the light is reduced to 12 hours with 12 hours of uninterrupted darkness (12/12), the plant "understands" that autumn is approaching and switches to the flowering phase.

Photoperiodic vs. Autoflower

Not all plants react to light. Autoflower varieties (self-flowering) transition into flowering on their own after a fixed period of time – regardless of how long the day is. This makes them less complicated, but eliminates the possibility of control via the light cycle. In indoor cultivation in a grow box, an uninterrupted dark phase is particularly important because light leaks can disturb the flowering of photoperiodic plants.

Frequently asked questions about the photoperiod

What do 18/6 and 12/12 mean?

The numbers represent hours of light/hours of darkness. 18/6 keeps photoperiodic plants in growth, while 12/12 triggers flowering.

Why is uninterrupted darkness important?

Photoperiodic plants orient themselves by the dark phase. Light in the middle of the night can disturb flowering.

Does this also apply to autoflowers?

No. Autoflower varieties flower time-controlled and do not react to the duration of light.