What To Do When Your Marijuana Plants Won’t Flower

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.

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.

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    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!

    Robert

    Robert Bergman

    Robert Bergman is an Amsterdam-based marijuana grow expert who has years of experience from small grows to massive operations. His passion for growing lead him to develop his own Gold Leaf strain. Now, Robert is dedicated to sharing his knowledge with the world.... [Read full bio]

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      78 comments on “What To Do When Your Marijuana Plants Won’t Flower”

      1. Ponder this: i have been growing pot since the60’s. During that glorious time in the 70’s when GOOD columbian ruled, I had no luck growing from Columbian bag seeds. They grew marvellous, tall plants that refused to flower. After the demise of GOOD Columbian and the birth of BC bud and Dutch seed banks, I never attempted to grow Columbian bag seed again. During that time, I successfully flowered African, Mexican and Hawaiian seeds.
        Recently, I purchased some Columbian ’72 seeds from a reputable seed-bank. Now they are WAY overdue finishing. They were started under lights on Feb 15 and relocated outside on April 25 and its now August.. The Columbian plants are grown among other varieties who have all have flowered . Some have even finished and are a month into curing.
        I believe that Because of Columbia’s vicinity to the equator, where ALL days are 12 hours long. all the time, something other or in addition to photoperiod helps trigger florescence. Therefore, especially with regard to cannabis grown at the equator, something in addition to light cycle encourages the beginning of florescence. If anybody had similar experiences with growing Columbian seeds and have figured out how to tip them to flowering, I’d like to hear it. BTW… low P or K is not an issue with my plants as exemplified by the adjacent plant’s success. Light leaks or midnight flashlight visits are also not an issue.
        Just wonderin’

      2. I have white widow seeds and northern lights and on 18 -6 and not flowering on week 8

      3. 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.

      4. Do I change my HPS 600globe to MH GLOBE growing autos or is the HPS globe sufficient??

      5. 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?

      6. 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″ plants (4) are doing great w the natural light. And my bill is back to normal.

      7. ? 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 I forgot something or do I need to be patient

      8. 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.

      9. 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 refuses to bloom. It has pistols protruding from between growth nodes but they aren’t growing any.. what gives?

      10. i am thinking of buying pop culture… for the bruce banner, skywalker and black widow strains. i have 2×3 tent… so i will only grow 1 each…. would be putting them outside for the summer…

      11. 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 on 03/31/2020. started 12 on-12 off on 04/22/2020. the plants shot up about a foot. and hope they go into flowering soon…. i am so looking forward to giving this strain too my friends!

      12. 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?

      13. 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 white Hairs by now, but im using a different breed plant.
        How much do nyou think this could set it back? Thanks. Frank.

      14. 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 12/12 for weeks now and still nothing. I just dont know why this one wont flower. Is it not an auto? Is its growth stunted. Or will it just take longer for this plant. I dont know why or what to do and I wish my lady with just begin to shine soon 🙁 I’m a first time grower by the way so it’s all a mystery to me that I cannot seems to solve. Any help would be amazing

      15. 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 I have to keep tying it up to keep it from falling over because it is getting heavy on the top. I’ve pruned leaves that have started dying or weren’t getting any light because the top ones were blocking it out. I water it once a day and drizzle a little bit of water on the leaves to help them keep moisture and they’re clawing at the very ends of the leaves. Its my first time growing and I keep running into problems and I’ve been tempted to just chop it for the past month now. Please help me before I make the harsh decision to just throw it outside and not grow again.

      16. 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 this with our great membership and staff for a more in depth and informed answer

      17. 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 in a flower photo period and hope for the best.

      18. 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.

      19. 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!

      20. 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 stretching and poping them perdy perdy pistols,now I don’t see no pistols.she ain’t wear back to the veg stage.I’m really hopeing I can get her back in

      21. 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 on for 2 days full and i have a very big commercial grow what should i do???

      22. 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 much better. See you there. Just tag me and I will catch up to you. Peace, lw

      23. 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… Just my issue is I have no clue what strain they are. They could possibly be seeds from my seeds and Stems days… Lol… what is my problem? I’m a indoor growing noob Beginner… Who obviously needs some help!

      24. 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 18on 6off. Something happened and they stopped producing the little white hairs. I went back to 24 hr lighting and still nothing. They r now getting so big soon they will b to big for there tent. How can I induce the flowering psyche again.? And do u think they were auto flower. ? I hope they r going to b ok!?

      25. 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.

      26. I have an outdoor Cannabis plant 6′ and it’s doing no flowering, what’s the problem?

      27. Zee,

        Hard to say with so little information. Go to: support.ilovegrowingmarijuana.com and let us help you there. Happy growing!

      28. 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?

      29. 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.

      30. 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.

      31. 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 two weeks are they beyond help i am in flowering stage about 5 weeks in

      32. 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 bit of root and then put I to the light they should be fine

      33. No it’s not the only light u can use in dark period is very dim green light honest I no from cruel experience

      34. Ha Tommy, glad you could save your plants with Robert’s advice. Good job! – I❤️GM

      35. 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.

      36. 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 get the same result; Right? Perhaps you can think about what you may have done differently. Have you contacted the seedbank you bought from? Perhaps next time, you will try some of Robert’s genetics. 😀

      37. 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 last crop I ditched the CFLs and bought balanced LED bulbs. I also covered the whole rig with a black plastic trash bag every dark cycle to insure NO LIGHT LEAKAGE (even tho the same environment successfully produced all those earlier crops). It’s been two weeks since entering the 12/12 cycle and not a single flower has appeared at the branch nodes. The crops were all from feminized seeds of the same strain (from Amsterdam). I’ve only grown from their seeds (Barney’s Farm) and half of my 10 successful crops were this same strain. I really need some intel to turn this around.

      38. Lannie,

        Small bubbles are much better than big air moving water. You need to get some air stones. Happy growing 🙂

      39. 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

      40. 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 toxicity, then perhaps you will just want to run plain water ph’d at 5.8 for a couple days. After that; Mix a full strength solution and watch the new growth for continued issues. If new growth is fine, all is fine 🙂

      41. 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 12 hours to change out her nutes- or turning on lights and changing her nutes now, then getting her back into darkness. Her sister Girl 1 (who is doing fine) will also get exposed to light. I don’t have a green light right now.

      42. 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; PLants also need 6-8 hours of rest everyday.

        Best advice I can give you: Join our support forum and learn how to grow guided by our many knowledgeable members and expert staff.

      43. 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

      44. 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 12hrs of light outside then I take it indoors for 12 hrs of darkness, what should I be doing help me out my first time.

      45. 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 will it hurt the plants if we commit to our camping trip for 3 nights. Basically 12-12 will be interrupted to 17 hours light and 7 hours dark for those 3 days. Should I cancel the trip?

      46. 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 cycle to show their sex. Good luck

      47. 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 long people had computers readily available ? i have grown weed for over 30yrs on and off , now thankfully people believe cannabis has helped slow down those dirty fucking cunt cancer bastards and beat the dfccb given the green fingered ability to help ease pain for others satisfied my selfish nature for now .

      48. […] 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 […]

      49. 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 but been fighting plant problems (yellowing faded leaves) I thought it was bug,root,or ph. Problem is have had issues for a good 3 weeks n one of my plants I thought should have been done by now is not they have developed nice dense buds but now look like they are dying I fixed the 12 n 12 thing so on proper light schedule am I waiting my time are these plants ruined?

      50. 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 switch the lamp/bulb when you induce flowering.

        Join our forum where we have links to many different lighting options, and a whole bunch of helpful members to address all your grow issues.

      51. Ive got a 400 watt sodium halide light Im using to veg. Do i need to change my light for flowering??

      52. 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 on line to try to determine the sex of the plants but they aren’t displaying any signs nor any differences among them. I’m ready to get them from the vegetative stage
        into the flowering stage., I’ve changed out the build to a 600 watt super HPS with higher red spectrum. I am moving the plants back to 12 hours on 12 hours off intervals. But how do I determine the sex? When will they show signs to help me determine the sex? And can I push them into flowering before I determine the sex? Help help help!

      53. 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 to get started.

        Then, You should join our support forum. Search and read 5 or 6 topics on starting seeds, propagation, etc. We will be glad to guide you from start to finish at ILGM Support.

        Happy Thanksgiving to you also. Sorry it is the day after. Peace

      54. 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 plants.

      55. 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 that’s Korat). Well I am having trouble with getting my seedlings sprouting up I’m a novice beginner so any help that anyone can offer would greatly be appreciated.
        Thank you for that.
        Happy thanksgiving to you and your family.
        Kevin Matthew Wall

      56. 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 in flower to see the “Blue” 🙂

      57. 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 to reverse the schedule in the middle of my grow. Even though I have green lights to work in the tents its still much easier to see and work under the grow light lighting for me. I don’t have any temperature issue’s now that its winter months and would like to be able to see and work during the day with the grow lights lit. Would it harm my plants to switch the lighting 180 degree’s in the middle of flowering? On during the day and off at night?

      58. 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.

      59. […] 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 it won’t flower properly. Read more about dark cycle interruptions. […]

      60. 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

      61. tomatoes plants started out slow cause of no nutrients until about 4wks in when should I start flowering?

      62. 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 lot of good stuff at advancendnutreints.com they have ph perfect now works great and its cheap sanesaint420 im out goodluck

      63. 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 fourteen hours for several days now…maybe a week. Plants are at the end of week three.Have just noticed the problem in the flower.(smaller than usual at week three) I have five weeks left. What are my chances of recovery?