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The Science of Light Deprivation for Plant Growing

June 10, 2016

Light deprivation is the procedure of coercing plants to blossom at the time of the year that would not typically be a period of flowering in the sun’s normal light progression. You can control the budding cycle by hindering the sunlight and making the plants believe it is time to flower. This is comparable to regulating the indoor light cycle by turning the grow light on and off.

By using an opaque curtain or tarp to deprive the plants of red-light spectrum at the beginning or end of summer days, growers are able to allow their plants to begin developing buds months earlier. The use of light deprivation techniques has become widespread in the U.S. due to the increasing popularity of medical cannabis. However, this practice has actually been in use for centuries with other crops.

Scientists still don’t completely comprehend why seasonal changes in the length of days induce flowering in plants. However, what we do know has helped growers produce better cannabis, and more efficiently, for decades.


How does it work?

The term “photoperiodism” describes how plants react to light and darkness. Simply put, cannabis plants shift to a flowering stage in response to the longer nights in autumn—generally around the time of the autumnal equinox, when the photoperiod is equally balanced. This means 12 hours of day and 12 hours of night. The absence of red light in the evening causes the accumulation of a plant hormone called phytochrome. The period of darkness provides sufficient time to build up the phytochrome. Once phytochrome reaches a certain threshold, it triggers the plant to switch to a flowering stage.

When flowering, plants respond to the length of the night, not day. When the light starts to surpass 12 hours a day, flowering plants can be at risk of returning back to their vegetative stage. This makes the process used for light deprivation vital for cannabis cultivators who depend on well-timed crops. Even a small amount of light during dark periods can stress and confuse the plant and inhibit its growth and potency. This could even cause the plants to become hermaphroditic, growing male flowers as well as smaller buds. On the other hand, a small amount of darkness during the day will not affect the plant or disrupt its flowering.

Flowering occurs in harmony with the circadian rhythm of the plants, which results in the time with an internal clock set to a 24-hour schedule. It does not matter what season of the year it is or whether your plants experience constant conditions. Plants like cannabis, which use the photoperiod to regulate flowering, are more sensitive to a disruption in that internal clock if they are grown under 24 hours of light.

Your plants require a certain amount of DLI, or “daily light integral,” to thrive. An inexpensive spectrophotometer can give you a great estimate of your DLI. This will provide a “saturation point” for your cannabis. Once this saturation point is reached, you know that the plant does not need further light except to maintain the light schedule.


By Kelly Martin

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