Light & Light Cycles
Photoperiod
Photoperiod is the amount of light and darkness a plant receives each day, which controls its growth and flowering cycles.
What Photoperiod Means for Cannabis Plants
Photoperiod refers to the duration of light and dark periods within a 24-hour cycle and how plants respond to those light patterns. In cannabis cultivation and horticulture, photoperiod is a key environmental signal that regulates vegetative growth, flowering, and overall plant development.
How Photoperiodism Was Discovered
The scientific study of photoperiodism began in the early 20th century, when researchers discovered that plants respond more strongly to the length of darkness rather than light alone. This led to the classification of plants into short-day, long-day, and day-neutral types. Cannabis is considered a short-day plant, meaning it begins flowering when nights become long enough.
How Photoperiod Triggers Flowering in Cannabis
In photoperiod cannabis varieties, flowering is triggered when uninterrupted darkness reaches approximately 12 hours. Growers replicate this naturally occurring signal indoors by changing the light schedule from 18 hours of light and 6 hours of darkness (vegetative growth) to 12 hours of light and 12 hours of darkness (flowering). Maintaining consistent darkness is critical, as light leaks during the dark period can delay flowering or cause stress responses.
How Photoperiod Influences Plant Hormones and Growth
Photoperiod affects more than flowering. It influences hormone production, particularly phytochromes (light-sensitive proteins that help plants detect day length). These hormonal shifts guide stem elongation, leaf development, and bud formation.
Using Photoperiod to Control Plant Timing and Yield
Photoperiod management allows growers to control plant size, timing of harvest, and yield. Outdoor cannabis plants naturally flower as daylight hours shorten in late summer and fall, while indoor growers have full control through artificial lighting.
How Autoflowers Differ From Photoperiod Plants
Autoflowering cannabis varieties differ because they flower based on age rather than photoperiod, making them day-neutral and less sensitive to light schedules.
Why Photoperiod Knowledge Matters for Growers
Photoperiod is closely related to light cycle, pre-flower, stretch, flowering stage, and autoflower. For cannabis growers, understanding photoperiod is essential for timing growth phases and achieving consistent, predictable harvests.
Related terms:
Light Cycle, Photoperiodism, Vegetative Stage, Flowering Stage, Pre-Flower, Phytochrome, Autoflowering Cannabis, Light Schedule.
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