≡ Menu

You're Here: Home » How to Grow » Flowering » Flowering Light Cycle

Flowering Light Cycle


The Flowering Light Cycle is the cycle you set your High Pressure Sodium Lights on to bud your marijuana plants. There is a basic light cycle and a more experienced growers light cycle for flowering and harvesting marijuana buds. In order to become successful with indoor marijuana growing, you need to know what light cycle to set your grow lights on as well as how many hours a day and how often they come on. I will show you a light cycle that will save you 50% of your production costs while gaining 30% more production, as well this advanced light cycle will cut your vegetative and flowering time by 25%.

Basic Light Cycle for Flowering Marijuana

The most common and basic cycle to set your high pressure sodium lights on for marijuana flowering is the 12 on 12 off cycle. This 12 hour light cycle is the maximum amount of light you should ever give your marijuana plants when they are in the flowering stage, producing marijuana buds. Anything more than 12 hours of light will signal the plant to continue growing in the vegetative stage, not allowing the plant to bloom and flower buds. I prefer to run my bud lights or flowering stage lights at night when the temperature is cooler for the indoor garden. If you are growing illegally, you may want to consider putting your lights on from 6pm-6am as the electric company employees do not work those hours and will not ever see your electric meter spinning at a fast rate.

Advanced Flowering Light Cycle

This advanced light cycle will save you time, money and increase overall production by up to 50%. This flowering light cycle is based on plants that are a 9 week flowering strain. Heres a breakdown of how you should set your timers for your HPS lights in your flowering or bud room:

Weeks 1-2: Set your timer for 11 hours on and 13 hours off.
Weeks 3-4: Set your timer for 10.5 hours on and 13.5 hours off.
Weeks 5-6: Set timers on for 10 hours and off for 14 hours.
Weeks 7-8: 9.5 hours on and 14.5 hours off.
Week 9: set timers to 9 hours on and 15 hours off. this is the final week of flowering and you should be “flushing” your plants to remove all chemicals and nutrients from the roots.

This is the best and most efficient way to set your timers for the Flowering Light Cycle.

How People found this article:
  • can i put my plants on a 10 hour cycle
  • 10 weeks of blooming cannabis
  • lighting time in the marijuna
  • should i turn my light off at night for my weed
  • weed lighting increse time flower
  • what can i do to increase my yield at week 6 of flower
  • what happens last week of flowering
  • what if i cut cannibis plants down at 6 weeks instead of 9
  • What if the lights were turned off and on one time during flower
  • what is my light cycle when growing

31 comments… add one

  • Noob Grower April 22, 2013, 6:26 pm

    Im new to growing actually really new, I’m doing an indoor grow and trying to figure out with little to no resources I’ve germinated my seeds and planted them in good soil but as of right now the only light they are getting is when the sun is out and they are in the window, We have a snake that uses a ZooMed Red Night light lamp and I was wondering if that would help the plant I’ve done research and cant find much on it, I’m currently out of work so I’m trying to find the best method for this, I’m not to worried about the yield or thc content just trying to grow to see how to do so, any weird info is helpful.

  • beth April 9, 2013, 1:40 pm
  • peter January 15, 2013, 6:08 pm

    what is 12/12

    • dizzle January 19, 2013, 9:56 pm

      light cycle

    • flynny January 25, 2013, 8:06 pm

      would the buds get any better affect, after about a month of 12/12 could you put it to 18 dark and 6 light?

      • dizzle February 4, 2013, 1:06 pm

        no if anything they will probably go into shock and hurt the thc levels

  • mark January 8, 2013, 6:45 pm

    yes i’am wondering if those times for the flowering cycle are right or did they get mixed up seems more light should be used for bigger buds can you let me know ty mark

  • curious November 8, 2012, 3:58 pm

    My flower room has been on 12-12 during the day, but I need to change it to nights. What is the best way of going about this. I have perpetual flowering, so in between cycles doesn’t work as there are no in between cycle times.

    • dizzle November 8, 2012, 4:05 pm

      just change it now. it wont hurt it. if you want it on from 6pm-6am, then u should just set the timer for that. It will be ok!

      • curious November 8, 2012, 4:11 pm

        Thanks. Just to verify, I simply kept them in the dark for 24 and will turn on the lights to start the 12-12 up again this evening. Just hoping I don’t get seeds from the 24 hours in the dark for the one day!

        • dizzle November 8, 2012, 4:22 pm

          u wont get seeds from the one day.. if your timers were on from 6am-6pm (mornings) all you need to do is let the light stay on after 6pm and then program it to come off at 6am the next day. then after that they will be on new schedule.. one day of “re-scheduling” them will not hurt anything

  • grant July 16, 2012, 7:47 pm

    Im new at this how long after i plant the seed do i put light and how long then i start 12/12 or whats the quickest way to harvest

    • dizzle July 21, 2012, 6:55 pm

      watch my videos! light is needed immediately. depending on the strain and how big you want them will determine when to start the flowering.

  • Adam April 27, 2012, 9:53 pm

    Have used advanced veg cycle (12-5.5-1-5.5) to great success from clone. Can this also be used from seed and if so when do you start it?

    • dizzle April 28, 2012, 4:46 pm

      yes u can use this anytime as long as the plants are healthy enough to start flowering.

  • paranoid stoner March 28, 2012, 1:02 am

    Can I use the sun for part of the 12_12 time for flower cuz I only got flourescent tubes which I will use warm white for flower also

    • dizzle March 29, 2012, 12:49 am

      u could although going from sun to flourescent may cause the plants to go into shock. maybe test it on 1 for a few days make sure it works

  • Hayzie March 22, 2012, 12:07 pm

    Can anyone can tell me, I came back to find my Hps lamp hadnt come on at the time it was meant too, it was off for 3.5hours over the time it should have fired up, my worry is; its 4 weeks through the 12/12 cycle. Does that sound like it will cause a problem to the crop?

  • Paul March 19, 2012, 4:23 pm

    I have 3 strains going. One matures around 7 weeks so when should i start flowering? The other says its ready to be harvested 8-9 weeks from seed so when should i start flowering her? Both are feminine and are said to have short flowering times

    • dizzle March 20, 2012, 12:14 pm

      start whenever u want . the loger u wait, the taller and bigger the plant will be.

  • Adam March 12, 2012, 12:02 am

    Hi. This is for Dizzle hopefully. Very quickly, I have taken as much of your advise as possible. Far more experienced growers than myself mocked me and doubted the light cycles until they saw results. Now they are doing the same. What I would like to know is what flowering cycle do you use for a 6 week or an 8 week flower. Is there a formula, do you just knock 2 days off per week or just knock off the last week of 9 hours. Thanks again, your videos especially have helped me get through what has been a very successful first grow.

    • dizzle March 13, 2012, 7:43 pm

      plants with quick flowering times like 6-8 weeks, i just use the 12/12 cycle the entire time.. works the best!

      • Adam March 13, 2012, 7:57 pm

        OK, help me out here, I have plants that are 8 week cycle on 13/11 2 weeks in, would you just keep it at that or reduce light by half hr increments ?

        • dizzle March 13, 2012, 8:58 pm

          just keep it. nothing wrong with it

  • Coreen Radilla March 10, 2012, 2:45 pm

    Do not let your ego get too close to your role, to ensure in case your position gets shot down, your ego doesn’t go along with it.
    Regarding the time we are able to make the payments, somebody moves the ends.

  • toris March 8, 2012, 1:40 am

    what does purple stems generally mean

  • Dr green thumb March 7, 2012, 5:17 pm

    For one you should have a light cycle of 18 on 6 off this give the plant time to stableize it’s root system and harden it’s stems to get ready for heavy flowers, but yeah basically when ever you want to put a plant into flower go for it but it will effect the yield, bigger plant bigger and more flowers, also do you know what the ph level is?? And what kind of food are you using (N-P-K) and are they green all the way through or is there yellowing, purple stems, dead spots anything going on besides a pure bright green?

  • scoob March 4, 2012, 7:37 am

    I am a newbie my plants are a bout 6 weeks old my light cycle been on 24 since day 1 they are a bout 2 feet tall is it time to bud .

    • dizzle March 8, 2012, 12:07 am

      ya i would have started flowering a few weeks ago~

  • MJ December 8, 2011, 11:02 am

    ok i just need to know how long is to long to have a plant in flowering.at the end of Dec,will be 16 weeks,that my 4 plants have been in florwing and only one has 60% of hairs have changed color the other three plants hairs are still very white showing and dont look no were nere ready.so do i leach now and wait two weeks to cut.and i know about trec but my two year old droped my jewlers loop it in the bathtub.

    • dizzle December 8, 2011, 5:58 pm

      thats way too long (16 weeks) ive never heard of anything that long except for outdoor strains that grow 7 feet tall.. i would just wait until the trichomes tell you they are ready for harvest… thats really the only proper way to do so..

Leave a Comment