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It is a well-known fact that marijuana plants use light as energy. Light schedules play a huge role in determining the stage of life of your plants. Marijuana plants will not begin producing buds until the flowering stage. During the vegetative stage, your plant is just a baby, so it is only growing leaves and stems with no buds. Read the article to find out why your plants aren’t flowering.

Vegetative vs. flowering stage

cannabis vegetative vs. flowering stage

Special organs inside leaf cells called Chloroplasts secure the red and blue light from the visible spectrum of light and use those to start photosynthesis. During photosynthesis, plants take certain elements from air and water to produce sugar while also releasing oxygen.

A marijuana plant growing outdoors will do just fine in lots of sunlight and begins flowing in the fall. But when it comes to big, compact indica buds, the plants grown indoors require about 40 watts of HPS or MH light per square foot. However, sativa buds require around 60 watts. In the first stages of growth, you can use both the HPS and MH lamps. You will need to change the light schedule for indoor growing to get your plants to start flowering.

There’s no way around this process!

Fluorescent light are fine for the vegetative state and the flowering period. When your plant is in the vegetative state, you will use cool, white fluorescent lights and when it reaches the flowering state, use warm, white fluorescent lamps. HPS light is good for generating flowers when the plant is in the flowering stage.

Flowering problems and solutions

dark cycle interrupted cannabis

Forcing your plant to flower
If you shifted the light schedule to 12 hours of darkness/ 12 hours of light and a few weeks have passed with no flowering, there are 3 possible causes. Either your grow rooms has some light leaks, the lights were on for too long or the light may have been on at the time there was supposed to be darkness.

Do your best to stick to the proper light cycle. If you need to go into the garden during the dark time, use a green light.

Fluorescent burn the leaves
If you are using fluorescent lights to grow, then it is necessary that your plant stays at least a few inches away from the lights. So long as this rarely occurs little harm will be done. If you experience light burn frequently, you can wrap a wire barrier around the tube to makes sure the leaves never touch the light.

What if the darkness or light cycle is disrupted?
Darkness Cycle: Let’s say the lights were accidentally left on for a full day, then this won’t be  too much of a problem. Now, if the lights are on for a few days consecutively at the beginning of the flowering period, you may notice your plant returning back to the vegetative stage. Your plants are not as damaged by too much light when they get close to being fully developed.

When the light schedule is thrown off, get it back on track quickly to avoid further problems.

Light Cycle: When the lights are off for a day or two, you will notice the buds are maturing faster and that is okay. Just turn then on again and carry on with your regular schedule until they are fully matured.

Both Cycles: So, if the light are turned on and off intermittently your buds will become scrawny and could potentially become hermaphrodites. Check out our articles on hermaphrodite plants to learn more.

If you need to, just use a timer to make sure the light schedule is constant.

No flowers on indoor plants
So, your indoor plants are not flowering? Offering your plants 12 hours of darkness a day without disruption for 5 days will producing flowering. Depending on the seeds you use, you may need continue this cycle for longer. It is important that this schedule if followed exactly the same each day. It’s best to have a timer for your lights to prevent unexpected mistakes.

Remember, to make sure your plant thrives during the flowering stage you need to adhere to the light schedule. Proper lighting is essential to your plants health. Too many mishaps with the light cycle could result in damage to your plants.

Thanks for reading. Please leave comments or questions below and don’t forget to download my free grow bible

Robert

46 Comments

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  1. By jacque

    ,19 Oct 2013
    I enjoyed your answers to the light cycle disruption. Plants will continue to or bud as soon as the problem is addressed but there will definatly be damage recovery time,and lots of “h”. My timer we forward two hours to […]Read More
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    1. By Charley

      ,05 Dec 2015
      I’m going into my 4th month . My plant are beautiful 3-4 feet tall. They are all the same height. It’s getting very crowded in my grow tent and they still all look the same. I’ve looked at the pictures […]Read More
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      1. By tyler

        ,22 May 2016
        Just wait to see if the two pistils start to emerge at the nodes, or it will have the bananna looking pods which would be the males. Ive never seen it take more than two weeks after beginning the 12/12 […]Read More
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    2. By Larry smith

      ,17 Mar 2016
      My timer has little depressers and somehow a few of them got pushed down in turn causing the lights to come on for a couple hrs during the 12hrs of dark not sure how long this has been going on […]Read More
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  2. By sanesaint420

    ,02 Jan 2014
    you shouldnt have a problem just keep that 12 an 12 going i go 12 an a half dark 11an a half light dont feed her the last two weeks give her some sweetner like blackstrapmolasas you can find a […]Read More
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  3. By ebee

    ,18 May 2014
    tomatoes plants started out slow cause of no nutrients until about 4wks in when should I start flowering?
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  4. By Jason Kaye

    ,11 Feb 2015
    Outdoor over 4 months 12 and 12 for 2 weeks flowering everywhere can i get away with keeping outside now all the time 24 hrs a day or will it re veg
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  5. By Problems That Cause Marijuana Plants To Stress

    ,15 Jul 2015
    […] Before flowering begins, every cannabis plant needs to undergo a period of uninterrupted, total darkness. Every strain is slightly different in this regard, but be absolutely sure that the plant isn’t getting any light during this crucial period, or […]Read More
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  6. By Symptom Checker – Identify Marijuana Plant Problems

    ,24 Jul 2015
    […] Plants won’t Flower […]
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  7. By Matthew

    ,12 Aug 2015
    If my plants are outside, and I turn on the outside light when its dark. Will those light disturb the bidding process? They are just standard lights.
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  8. By latewood

    ,14 Aug 2015
    Any time you disturb the dark period of photo synthesis; You can expect potential issues.
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  9. By Paul Malczewski

    ,24 Oct 2015
    During the summer months, I was fine having my lights on at night. 9.00 pm to 9.am on, 9.00 am to 9.00 pm off. It kept the grow tents temperature manageable. I’m wondering if it would be an issue now […]Read More
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  10. By latewood.ILGM

    ,27 Oct 2015
    Paul Malczewski I suggest you enjoy the lower temps provided by fall/winter, in order to grow in an easier to deal with environment. Keep your photo period on the same schedule. Maybe grow some Blueberry, and attempt to chill it […]Read More
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  11. By tank

    ,24 Nov 2015
    Is it ok to interrupt an indoor grow at night/ dark period with a white led flashlight or headlamp
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    1. By latewood.ILGM

      ,27 Nov 2015
      Hey Tank, “my Pitbull’s name” lol It is never advisable to interrupt the dark cycle with an intense white light. Green filtered light is the only light advisable to use in the dark photo period in order to examine the […]Read More
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    2. By Bob potter

      ,29 May 2017
      No it’s not the only light u can use in dark period is very dim green light honest I no from cruel experience
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  12. By Kevin Wall

    ,27 Nov 2015
    I’m just starting out and just bought a killer hydroponics machine and now have put one plant in already seems to be doing fine. Oh by the way I’m in nakonratchasima, Thailand ( for people that don’t really know Thailand […]Read More
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    1. By Tom potter

      ,30 May 2017
      Make sure the seed has good genetics if the the seed is good and viable you should have no prob keep it moist not wet in whatever medium you have keep in the dark till you see a little white […]Read More
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  13. By latewood.ILGM

    ,27 Nov 2015
    Well Kevin, I am not sure what you are asking for. I see that mention problems with seedlings, but that is rather vague. I suggest you download and read our Free Grow Bible. It has all the info you need […]Read More
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  14. By Calvin

    ,22 Jan 2016
    Ive got a 400 watt sodium halide light Im using to veg. Do i need to change my light for flowering??
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  15. By latewood.ILGM

    ,23 Jan 2016
    We use Metal Halide for Veg cycle, and switch to High Pressure Sodium for Bloom cycle. Not sure what is sodium Halide. I have both type lights. Recently I have invested in Digital Switchable ballasts, and all you do is […]Read More
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  16. By Light Deprivation: Pro vs. Con – Daniel J. Monk

    ,07 Apr 2016
    […] 12 on 12 cycle. If for some reason this process gets screwed up the plants can get seriously damaged as they get shocked back into the vegetative state. A cure for this is automation, but that is […]
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  17. By graham

    ,24 Apr 2016
    hi , new grower just poking about for clues and refreshingly have had luck today , stumbling upon your page on this thing , am philistine and not keen on change have only just accepted typing for a bloke ,how […]Read More
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  18. By Mr. M – Vancouver

    ,24 Jun 2016
    I have 2 GG#1 plants from feminized seed in large pots in ~3rd week of budding, outdoors, with the plants in a homemade patio darkroom, which I open at 7 a.m. and close at 7 p.m.. My question is….how much […]Read More
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  19. By gladiator

    ,25 Jun 2016
    I started my plants from seed. I took them outside to be in the sun all but one is in veggie stage. one of them is flowering and its only seven inches tall full of flowers, I let it get […]Read More
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  20. By Acy first grow

    ,14 Sep 2016
    My plants won’t flower I’ve done the 24 hr darkness and I’m on 12/12 my babies are 2 1/2 months old please help
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  21. By latewood.ILGM

    ,15 Sep 2016
    Acy, It takes 10-20 days after changing light photo period to 12/12 in order to induce flowering. You should never grow plants under a 24/0 photo period. Plants use the same minerals as humans to grow, and as humans do; […]Read More
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  22. By CharlieTool

    ,02 Oct 2016
    I started 12-12 on my hydro grow 4 days ago. The girls just started their dark period by timer within the past 30 minutes. I have diagnosed nitrogen toxicity and now want to flush Girl 2. Which is worse- waiting […]Read More
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  23. By latewood.ILGM

    ,04 Oct 2016
    If you cannot change out solution in dark, you have to wait, or risk exposing all plants to the dark period interruption. Not sure why you did not see this when lights are on… If you really have a Nitrogen […]Read More
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  24. By LANNIE PINSON

    ,26 Feb 2017
    My girls are 2 weeks old and I realized the air pump it was withou the air stones for oxygen can it still survive. Strawberry KUSH
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    1. By latewood_ILGM

      ,28 Feb 2017
      Lannie, Small bubbles are much better than big air moving water. You need to get some air stones. Happy growing 🙂
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      1. By CPS

        ,19 Mar 2017
        I have an ongoing problem with plants not transitioning – 5 grow cycles in a row have failed to transition. I grow 1 or 2 plants in a small hydro rig. My first 10 crops all transitioned no problem. This […]Read More
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        1. By latewood_ILGM

          ,20 Mar 2017
          CPS, It just sounds like you are being impatient. It generally takes 2 weeks to start to see pre-flowers, but it can take longer. I suggest you be patient. On the other hand if all was the same, you would […]Read More
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  25. By Tommy

    ,25 Apr 2017
    Yet again you saved the day Robert. Just when i think i need to scrap my current plants and start over AGAIN. I have read all the articles you have sent me twice. Thanks for your help.
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    1. By Roy ILGM

      ,26 Apr 2017
      Ha Tommy, glad you could save your plants with Robert’s advice. Good job! – I❤️GM
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  26. By michel

    ,27 Apr 2017
    clear answer on the disruption of light cycle, thank you
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    1. By latewood_ILGM

      ,28 Aug 2017
      You are welcome. We have a great support forum, too! 🙂 ilovegrowingmarijuana.com
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  27. By tony

    ,21 Aug 2017
    some ass hole have altered my clock so they was burning indoors 24 -7 no light break. two of my plants have wiltered (leaves) rest are pointing up i have re set the clocks they have been suffering for about […]Read More
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    1. By aj

      ,23 Aug 2017
      Wilted leaves tells me you put them outside directly under sun (heat), they need nitrogen
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      1. By latewood_ILGM

        ,28 Aug 2017
        aj, Your reply is totally off base. Sorry, tips pointing up is heat exposure due to not enough watering and too much light and heat.
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    2. By latewood_ILGM

      ,28 Aug 2017
      tony, Thanks for sharing. All you can do is water them and correct the photo period timer issue, and wait. 🙂 Happy growing. p.s. You should not let ass holes in your grow room, or anyone; For that matter.
      Was this comment helpful to you?
  28. By Zee

    ,07 Feb 2018
    I have 4 autoflowers in week 10 that are all very clearly in flower for about 4-5 weeks with almost no bud development. Plants are large and bushy but the budsites won’t fatten up?
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    1. By latewood_ILGM

      ,08 Feb 2018
      Zee, Hard to say with so little information. Go to: support.ilovegrowingmarijuana.com and let us help you there. Happy growing!
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  29. By Paul Todd

    ,07 Jun 2018
    I have an outdoor Cannabis plant 6′ and it’s doing no flowering, what’s the problem?
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  30. By latewood_ILGM

    ,13 Jun 2018
    Paul, Most likely your days are still getting longer. After June 21st, days shorten and flowering can begin. Right now in most of North America we are approaching 14/10 days and flowering will nnot occur in this photo period.
    Was this comment helpful to you?
  31. By Rolland A. Berube

    ,02 Nov 2018
    Love all the info, being a first time grower. Thank u much!
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