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How do I manipulate the photoperiod for larger yields?

Photoperiod manipulation is a technique used to optimize plant growth by adjusting the duration of light and dark periods. This method has been experimented with for years, and one particular adjustment has shown significant improvements in plant growth and flowering rate.

The 21:36/12 Photoperiod​

The most effective photoperiod adjustment involves increasing the daylength to 21 hours and 36 minutes, with a 12-hour dark period. This adjustment should be made for 1 or 2 calendar weeks at the point of maximum flowering rate. To implement this schedule, you will need a 7-day, 24-hour digital timer.

Schedule for the 21:36/12 Photoperiod​

Here is the schedule to follow during a 7-day calendar week:

  1. Day 1: Sunday, 6:00 am to Monday, 3:36 am
  2. Day 2: Monday, 3:36 pm to Tuesday, 1:12 pm
  3. Day 3: Wednesday, 1:12 am to Wednesday, 10:48 pm
  4. Day 4: Thursday, 10:48 am to Friday 8:24 am
  5. Day 5: Friday, 8:24 pm to Saturday 6:00 pm
During this time, the "sun" will cycle only 5 times, allowing you to switch back to the regular 12/12 schedule at your discretion.

Benefits of the 21:36/12 Photoperiod​

Using this photoperiod during peak flower production offers several advantages:

  1. Increased light energy: The total increase in light energy is almost 80%, which can result in larger yields if all other environmental conditions are optimal.
  2. Extended flowering period: The total increase in the flowering period is only 40%, which means there is still room for improvement.
  3. Efficient use of resources: Applying the 21:36/12 photoperiod for 1 or 2 weeks extends the wait by only 2 to 4 Earth days, allowing you to provide additional light energy without purchasing extra equipment or overloading existing circuits.
When combined with optimal nutrition and CO2 levels, this photoperiod can dramatically increase plant metabolism.


The 21:36/12 photoperiod has been successfully tested for two weeks, offering the potential for a net increase of 40% over the entire cycle. This method harnesses an 80% increase in light energy and a 40% longer wait, making it a worthwhile technique for optimizing plant growth and flowering. Don't be afraid to give it a try!
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This is a concept i've recently been thinking about. I'm very Interested in trying an experiment with a 400watt in a 3x3 to test this out.
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