Definition - What does Photoperiod mean?

Photoperiod refers to the time that a plant or animal is exposed to light in a 24-hour period. Many types of plants require certain lengths of light exposure to enter various life cycle stages.

Growers frequently control the photoperiod in a plant’s life cycle through the use of grow lights to encourage the plant’s vegetative state, early flowering, bud phase, and ultimate harvest.

Some plants also respond favorably to a longer than natural photoperiod by producing a more abundant harvest yield.

MaximumYield explains Photoperiod

Indoor plants in the vegetative stage should ideally be receiving 18 hours of light and 6 hours of darkness in a 24-hour time period. This is represented as 18/6. This is only a recommended average; with some strains requiring more or less light or darkness.

When indoor-grown plants move into the flowering stage, the light period, or their photoperiod needs, change to 12 hours of light, 12 hours of darkness.

Most plant types are photoperiod dependent; however, there are some autoflowering genetics that are not photo-period dependent. In photoperiod-dependent plants, exposure to very specific periods of light timing is what triggers various plants to enter their life cycle phases.

Some plants are considered long-day plants. Long-day plants require days that are longer than their critical day length time to flower. Short-day plants will flower on shorter day lengths. In the middle, there are day-neutral plants, requiring equal amounts of light and darkness.

Plant cultivars have commonly been bred to require very specific photoperiod times in order produce a bountiful harvest. Some plants also only respond to a photoperiod when they are young and not upon maturity. Such plants simply produce flowers based on their age and not light exposure.

Photoperiodism and photoperiod are two related terms that are used interchangeably.

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