The relationship between light and dark (day and night) is called photoperiod.
Flowering begins when the days get shorter, while vegetative growth continues when the days are longer.
Vegetative plant hormones are produced by the plant 24 hours a day.
Plant growth and flowering are influenced by phytochrome hormones. These plant growth hormones are produced day and night, but the flowering phytohormones are broken down during the day by light.
The flowering phytochrome hormones dominate once the plant is in darkness, triggering flowering. In just 1 hour of darkness, the plant produces far more flowering phytohormones than vegetative ones.
The slightest light during this dark period can seriously disrupt or even stop phytohormone production.
That’s why it is important never to enter a dark grow room, even with a flashlight.
A plant needs daylight to capture sunlight for photosynthesis to generate energy.
~ 6H₂O + 6CO₂ + light → C₆H₁₂O₆ + 6O₂ ~
Simply put:
Water + carbon + light = energy.
The more light, the more energy the plant can produce, provided enough water and CO₂ are available. A plant therefore needs both light and dark.
The best balance to maximize flowers and fruits is 12 hours light and 12 hours dark.
How to get bigger buds?
If you leave the light on for 18 hours or more, the flowering phytohormones never dominate, and the plant will remain in the vegetative stage, continuing to grow.
This is how nurseries keep their mother plants.
Mother plants can even be kept under 24 hours of light, but this requires much more electricity for grow lights and delays flowering once moved into a 12-hour light cycle.
One trick some growers use is to extend the light during the last 2 weeks of flowering from 12 hours to 14 hours of light per day.
Two weeks before harvest, the plant has already built up enough flowering phytohormones to continue flowering. However, with 2 extra hours of light per day, the leaves absorb more light, produce more energy and sugars, and the plant has less darkness to consume energy.
This results in bigger buds.
There are also products available that contain a mix of natural phytochrome hormones to stimulate plant growth and flowering.
The best time to use these products is during the day, when the plant pauses in flowering phytohormone production.
How else can you play with light?
Sometimes, if a lighting system malfunctions and the lights above the buds do not switch off, the result is stem formation within the flower clusters.
After discovering the malfunction, the solution is to immediately switch off all lights for 24–48 hours, so the plant boosts flowering phytohormone production to limit the damage.
Growers who want to induce flowering in their mother plants should always keep them in complete darkness for 48 hours first. This prevents plants from stretching excessively under the lamps.
Some growers also turn off the lights for 24 hours around week 3 of the grow cycle to keep the plants shorter and trigger earlier flowering.
Metrop Green Xtrem is a blend of natural plant growth hormones.