What To Do When Your Marijuana Plants Won’t Flower

April 27, 2021

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

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.

HPS grow light during vegetative stage
HPS grow light

There’s no way around this process!

Fluorescent light is 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.

Download my free Grow Bible for more information about lighting for your marijuana plants.

Flowering problems and solutions

Forcing your plant to flower

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.

Fluorescent lights
Using fluorescent lights on marijuana plants

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 to continue this cycle for longer. It is important that this schedule is 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.

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FAQs About Why Cannabis Plants Are Not Flowering

Why is my cannabis plant not flowering?

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 room 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.

What are some ways to trigger my marijuana plants to flower?

Always follow the proper light cycle and make sure your plant stays at least a few inches away from the grow lights.

Have you had problems with the flowering of your marijuana plants? Please share your experience or leave questions below!

Happy growing!


The founder of I Love Growing Marijuana, Robert Bergman, is a marijuana growing expert that enjoys sharing his knowledge with the world. He combines years of experience, ranging from small-scale grows to massive operations, with a passion for growing. His articles include tutorials on growing... [read more]


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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
    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
      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
    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
    3. By Patriick ,10 Jul 2021
      I have white widow seeds and northern lights and on 18 -6 and not flowering on week 8
  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
  3. By ebee ,18 May 2014
    tomatoes plants started out slow cause of no nutrients until about 4wks in when should I start flowering?
  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
  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
  6. By Symptom Checker – Identify Marijuana Plant Problems ,24 Jul 2015
    […] Plants won’t Flower […]
  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.
    1. By Karl Pausblau ,07 Jun 2021
      That depends on the light spectrum the lamps use. Ifit is green light, it won't disturb the plants. If it's white, yellow, blue or red and it shines on the plants, that can disrupt their light schedule.
  8. By latewood ,14 Aug 2015
    Any time you disturb the dark period of photo synthesis; You can expect potential issues.
  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
  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
  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
    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
    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
    3. By Jason ,22 Sep 2020
      No! If you must go in at night, use a green light.
  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
    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
  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
  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??
  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
  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 […]
  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
  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
  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
  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
  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
  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
  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
  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
    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 :)
      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
        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
  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.
    1. By Roy ILGM ,26 Apr 2017
      Ha Tommy, glad you could save your plants with Robert's advice. Good job! – I❤️GM
  26. By michel ,27 Apr 2017
    clear answer on the disruption of light cycle, thank you
    1. By latewood_ILGM ,28 Aug 2017
      You are welcome. We have a great support forum, too! :) ilovegrowingmarijuana.com
  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
    1. By aj ,23 Aug 2017
      Wilted leaves tells me you put them outside directly under sun (heat), they need nitrogen
      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.
    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.
  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?
    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!
  29. By Paul Todd ,07 Jun 2018
    I have an outdoor Cannabis plant 6' and it's doing no flowering, what's the problem?
  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.
  31. By Rolland A. Berube ,02 Nov 2018
    Love all the info, being a first time grower. Thank u much!
  32. By LindZ ,03 Feb 2019
    I have 2 large girls that I was told were, Durban poison and current kush feminized seeds. They started flowering about 2 weeks ago, under 24hr, full spectrum lighting. I assumed they were auto flower. I changed the lights to […]Read More
  33. By NICOLE ,03 Jun 2019
    My cannabis plants have been growing since March 4th and I feel like I should be going into my flowering stage but they are only a foot Tall if that... Watered When needed. Good sunlight daily, humidity is... Eh, Nebraska... […]Read More
  34. By latewood ILGM ,20 Jun 2019
    Nicole, If you happen to have a land race sativa, it could takes months to flower. I suggest you join us here: support.ilovegrowingmarijuana.com where we can have a look and see what you are doing in order to help you […]Read More
  35. By Robert ,21 Jun 2019
    Thank you for the information was very informative
  36. By Phillip ,04 Jul 2019
    I had to move my plant inside at night because of deer then back out for sun
  37. By Nick ,15 Dec 2019
    Robert I am using your seeds BlackberryKush and Super Skunk also Durbon Poison i live you strains as i order many different kinds but i am about to hit week 6 of flower and i noticed my lights were left […]Read More
    1. By latewood_ILGM ,29 Jan 2020
      Nick. Either hire an experienced consultant, or join our support forum and post your question there. Basic answer. Keep them in the proper photo period and hope for the best. The damage if any, was already done.
  38. By Timothy ,16 Jan 2020
    I've been flowering for34dayz .no flowers.they been working on the breaker box an had to cut power 3or4 times an it messed my schedule all up.I do have a timer.it messed it all up.she was in tha prosess of her […]Read More
    1. By latewod_ILGM ,29 Jan 2020
      Timothy. Good Luck with you attempt. I usggest you join our forum in order to discuss options with many member and staff supporting new growers who need help. The damage was done so, all you can do is place them […]Read More
  39. By Rev. Glenn Greuling ,21 Jan 2020
    Dear Sirs, How tall does your Amnsia Haze get? And when will it flower? It started Dec.7 and now it's the 21st of Jan. THANX!
    1. By latewood_ILGM ,29 Jan 2020
      Reverend, PLants flower when the flower photo period is induced. Amnesia Haze can take 6 months total grow time to finish unless you manipulate the flowering photo period hsortening lights on. you really should join our support forum and discuss […]Read More
  40. By Justin ,18 Feb 2020
    Okay so I planted my plant 5 months ago and it still isnt flowering, i put it on a 12/12 cycle about a month n a half almost 2 months ago and still nothing.. it just keeps getting taller and […]Read More
  41. By Tre ,24 Feb 2020
    I started two of the same Autoflowers (blueberry) at the same time. one is doing well with buds growing nicely. But the other has tricomes or little white tendrils but its isnt doing anything else. I've had it on the […]Read More
  42. By Frank ,06 Mar 2020
    I fit an air con unit and it jas a blue display when it comes on. It wasnt really bright but just enough to see the plants. It’s been a week and no show of flowering when usually its showing […]Read More
  43. By Terror terry ,29 Apr 2020
    I have my tent in my living room. i have the flaps klipped shut. and very little light comes out. so when it goes into 12 off will the little light from my room be too much light?
  44. By terror ,29 Apr 2020
    i have amnesia haze [fem] seeds... being my first seeds from iLGM i planted most of them thinking that 1 or 2 would grow. but all of them took off... planted in solo cups on 02/29/2020 put in bigger pots […]Read More
  45. By terror ,29 Apr 2020
    i am thinking of buying pop culture... for the bruce banner, skywalker and black widow strains. i have 2x3 tent... so i will only grow 1 each.... would be putting them outside for the summer...
  46. By Robert ,25 May 2020
    I love your info/great stuff!! Thank You
  47. By terrrence ,06 Jul 2020
    what is the light cycle..after plants have flowered..??..more dark or light
  48. By JasonDubya ,22 Sep 2020
    I have 6 girls on my patio. 5 are super healthy and in their 4th week of bloom. The one plant was a runt and had deformed leaves as a seedling.. it grew into a 24” Bush, but now it […]Read More
  49. By Frank ,11 Oct 2020
    I have been growing for years now. I put my girls into a 12/12 flower cycle and all they are producing is pre-flowers. It’s been almost 3 weeks. Anyone know what’s goin on? Started from seeds from a reputable company.
  50. By John ,18 Jan 2021
    ? At 7 1/2 weeks plants are out growing environment so to force flowering we went 24 hours dark and now 12 on 12 off for 7 days with no change does not appear to be starting flower stage have […]Read More
  51. By Bentit696 ,16 Mar 2021
    I was using 1000watt full spectrum light during the night 12 on 12 off......my light bill skyrocketed for 3 months, coildnt keep up, i was actually thinking of just doing away with it all UNTIL i realized that my 8-12" […]Read More
  52. By Antonio ,04 May 2021
    I'm going into my 4th week flowering. All of my plants are growing buds, except one. It is flowering but not budding like the others. And no it's not a male! Do anybody know what might be going on?
  53. By Mat ,07 May 2021
    Do I change my HPS 600globe to MH GLOBE growing autos or is the HPS globe sufficient??

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