Photoperiodism refers to the sensitivity of a crop to the length of lighting cycles during production. Specifically, the length of the dark cycle, “nighttime”, heavily influences flowering behavior in a number of crops. The distinction between light and dark cycles is an important one: growers developed “nighttime interruption” strategies to take advantage of this sensitivity. Growers employ nighttime interruptions during short-day conditions, like those found during winter. The day period is left along, but the night period is broken up into two shorter periods separated by a very low intensity light period. These periods can last two to four hours. Plants “see” short nights, resulting in a long-day response. For some crops, flowering is initiated; for others, flowering is suppressed.
Special photoperiodic lighting fixtures are designed to deliver low light levels of red and far right light, which have been shown to be most efficient for this type of lighting. In the past, incandescent bulbs were used, though the use of LEDs ensures that electrical consumption remains low, maintaining a low cost of use. TotalGrow’s Pure Flowering 200 Lamp accomplishes this lighting and energy-use goal beautifully. A single fixture can cover about 200 square feet with the low light required. Growers need significantly fewer photoperiodic fixtures than supplemental or sole source lighting would require.
Several economically important CEA crops grown in greenhouses and other controlled environments display photoperiodic responses.
Strawberries – Certain strawberry varieties have strong photoperiodic responses. June-bearing strawberries produce runners during long-day, short-night conditions, while flowers and fruits are produced during short-day conditions. Photoperiodic lighting can be used for runner production in these varieties.
Cannabis – Cannabis is a short-day flowering crop, with production emphasis on the flowering stage as the end product. Photoperiodic lighting would be used to keep plants in a vegetative stage, suppressing flower formation. Maintaining a vegetative state is important for mother plant production, but high light levels may not be required. Growers may also find that extending the vegetative stage in production plants results in larger plants at the end of the flowering stage.
Edible Pansies – Pansies are gaining popularity as edible garnishes for many specialty dishes. Pansies flower under long-day conditions, in contrast to cannabis. Using photoperiodic lighting through winter months in the greenhouse can produce long-day conditions for year-round flower production.
If you’re wondering where to start in developing a lighting plan and choosing the right fixtures, reach out to your Griffin sales rep or GGSPro! We can help you get started down the right path.
From Oregon State University: Figure 26. Periodicity of plants. Short-day (long-night) plants require a long period of uninterrupted darkness to flower. Long-day (short-night) plants require a short period of uninterrupted darkness to flower.