Question: I heard from a friend that indoor growers can get more potent cannabis buds by slowly reducing the light period (experienced by the cannabis plants) each day for the last few weeks before harvest.
For example, I give my cannabis plants 12 hours of light each day for most of the flowering stage (as is considere the standard for flowering cannabis plants), then 3-4 weeks before harvest, I'd reduce that to 11 hours of light each day, then a few days later I'd change to 10 hours of light each day, etc. I'd keep going until they got 24 hours of darkness before I harvest them, then the day of harvest I turn the lights back on for an hour or two so they pump all their goodness through their veins into the nugs before I take the plants down.
I've heard that this light schedule manipulates the cannabis plant into thinking it is dying, therefore it will start doing what it needs to survive/stay alive, and the plant will work harder to live. Then the day before harvest, by turning the lights on for an hour or two you trick the plant into thinking it's alive and get a huge amount of extra "goodness" into the buds.
Will this technique work to increase cannabis bud potency? What does shortening the day length actually do?
Answer by Nebula Haze: Let me explain a little bit about cannabis plants, and I think that will help me answer your question. In the wild, cannabis plants are on a very tight schedule. Because these plants die every year, seedlings must emerge from the soil in the spring, grow very big very fast, then pollinate to make seeds in time for fall, when they naturally die off each winter. The seeds lay dormant through the cold winter and sprout the following spring to create the next generation.
The cannabis plant uses a special system known as "photoperiodism" to to determine when to mature and produce buds/pollen/seeds. Because they have to complete their whole lives in one year, the plants need to time everything right in order to grow for as long as possible during the spring and summer, then makes mature seeds in time for winter.
After sprouting, a young cannabis plant gets extremely big extremely fast, and grow only stems and leaves for the first part of its life, kind of like the "kid" stage, since the plant doesn't have any sex organs during this part of the plant's life. As the days grow shorter, the plants "sense" that winter is coming; male plants make pollen and female plants produce buds. The wind blows pollen on the female buds (which have wispy hair specifically made to catch pollen), which pollinates the female plants so they start making seeds.
Because of this crazy time schedule, cannabis plants need to keep everything is sync so that the male and female plants produce buds and pollen at the right time, and the female plants still have enough time to produce mature seeds before they die when winter comes. (On a side note, the buds we smoke are the result of female plants which have never been pollinated.)
When growers give the plants shorter light periods during the day, this is mimicking what happens in the wild. The shorter days "tell" the plant that winter is coming. In the wild, nights naturally get longer as winter approaches, and cannabis plants use a hormone system to keep track of how long the nights are. When nights start getting really long (days get very short), the plant starts maturing the buds very fast, because the plant "thinks" that winter is coming right away.
So to answer your question, when you give the plant shorter periods of light each day, you are causing the buds to mature faster. However, because the plant is getting less light (less time to make energy with photosynthesis) each day, the buds are going to be smaller than if the plant was given the longer periods of light. Also, the plant will mature faster, and so this also reduces yields.
In my experience, here are the cases when growers benefit from giving plans shorter light periods than 12 hours during the end of the flowering stage:
- For strains that come from the equator where light levels are often near 12-12 (usually sativa plants) reducing the flowering light period to 10-14 or even 8-16 is sometimes needed to get the plant to mature.
- Also for some Sativa and Haze strains, the normal flowering period is 3-4+ months, and shorter light periods can be used to "force" the buds to mature faster
- In cases of extreme heat, sometimes the yield loss from shorter light periods is worth the reduced heat, especially if someone is just trying to get their plants to survive until harvest
- Any other case where getting the plant to ripen faster outweighs the potential loss of yields, like if you knew you were moving to a new home soon
I normally wouldn't recommend shortening the light periods during the end of flowering unless you have a stubborn Sativa or Haze that just won't finish ripening, or if you have some reason you need the plant to ripen faster. Otherwise, I believe the only real result is reduced yields. I haven't seen evidence that it increases the quality of buds in any way. I haven't seen anyone run any tests or studies to check if this sort of technique somehow increases the resin/cannabinoid production. I will say that the growers around here seem to try and test everything to increase cannabinoid levels (since I'm in a medical states and all buds around here get tested for potency), and I haven't heard of any of them running one of these reduced light schedules at the end of flowering. I've only ever heard this technique get mentioned in the forums, never by a real grower in real life.
If anyone has actually tried this technique and gotten good results, I would love to hear more! I always love learning more about these amazing plants! Contact me here if you've got any pictures, studies, or other interesting information about this topic!