Allison Justice

Supplemental Lighting Techniques Could Introduce A Brave New World Into Growing Cannabis

Supplemental Lighting Techniques Could Introduce A Brave New World Into Growing Cannabis

Growing marijuana involves the vegetative state when the plant is carrying out photosynthesis and accumulating resources. After that, is flowering and reproduction.

If you’re growing indoors, you apply over 18 hours of light per day to keep plants vegetative —and after 4-8 weeks change your light timer to a 12 hours schedule to induce flowering. Sometimes growers leave their plants in the vegetative stage for a longer time, in order to take cuttings from it and make clones of that “mother plant.”

Cannabis is an annual plant –its flowering period is determined by the seasons and their changing photoperiods. When the cycle ends the plant dies.

Recent studies around “night interruption” —the practice of providing low-intensity lighting to plants during the middle of the night— and supplemental lighting are suggesting effective methods for farmers to increase their yield year-round and to have more control over their crops. For example, in warmer climates, growers can run multiple cycles per year without the need for a greenhouse or blackout cloth.

For “short-day” crops (Cannabis, poinsettias, and garden mums) —the plant becomes reproductive under short days/long nights. By interrupting the dark period, the plant will then think it’s a long day. If you were to turn your grow lights on for only five minutes in the middle of the 12-hour dark cycle (sometime between 10 p.m.-2 a.m.), your plants will stay vegetative.

Farmers are using supplemental lighting techniques to keep cannabis plants from flowering too soon. By utilizing night interruption, farmers in Baton Rouge can potentially keep their plants vegetative for one to two weeks. While the farmer is paying the same amount per seed or liner, the yield will be dramatically different.

A map produced last year by plant breeders and the University of Tennessee gives farmers a guide to understanding daylength and the dangers of frost for planting and harvest.

With a better understanding of why certain varieties perform differently at varying latitudes growers can manipulate that in a cost-effective way. Understanding how to manipulate these plants with light provides a whole new way of growing, with the potential to have many crops per season.

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1 comment


Great article.

I’m a home grower, ive got some clones I planted outside in south africa and the plants are flowering too soon. they came out of a full light grow room but I did try slowly adjust them to natural lighting before transplanting outside. A month later they are starting to produce buds. I could wait to see if they move through it and return to veg as we are in mid summer with 15 hours of light in a day. Or I can try use the light interuption method to ensure I bring them back to veg sooner. How many nights do I use the night interuption for? Is it for one night, a few nights or continue until I want it to flower in 3-4 months time?

Much appreciated

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