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When Do Marijuana Plants Start To Flower?


Flowering Basics

Of course, getting to the flowering stage is different for every plant. If you’re growing indoors, then you have control over when the plant will start flowering. If you’re growing outdoors, however, the plants will only start flowering once certain lightness and darkness quotas are met. Unless you’re using an auto flowering variety, thedank marijuana floweringn having a set amount of complete darkness every night is necessary to get the plants to flower. During vegetative growth, you might leave the lights on 24/7, but when the plants have matured enough, you’ll want to switch them to a 12/12 light to darkness ratio. That means, the lights stay on for 12 hours and they go off for 12 hours straight.

It’s important to note that flowering will only occur in situations where the plant receives total darkness for approximately 12 hours. If you interrupt the darkness period even for a few seconds, you may trick the plants into thinking they’re getting more light. It should also be noted that certain varieties have “thresholds” of darkness that need to be passed. That is to say, 12 hours might not work for some plants. You might even be able to get away with a smaller length of time in the dark (say, 10 hours), and you may even need to provide as much as 14 hours of darkness.


If you’re growing outdoors, then you may be at the mercy of the of the Earth’s tilt. Varieties that have extra-long darkness thresholds will have to stay outdoors for a longer period of time. If applicable, you can but a blackout sheet over the plants so that they get the recommended amount of darkness, but that won’t always work. Download my free marijuana grow bible for more tips.

Once the actual flowering process begins, you’ll start to notice distinct changes in plant growth and behavior. Male plants will differentiate themselves from female plants by creating pollen sacs rather than pistils. Male plants often tend to grow larger, earlier so that they can drop their pollen onto the female pistils and promote reproduction. Both males and females will have internodes that extend. Male flowers are rather small and they have a yellow, red, purple, or pale green color to them. Female flowers are characterized by two hairy, white stigmas that are designed to catch the male pollen. Over time, the female flowers will begin forming clusters that are referred to as “buds.”

In general, the plants will become more robust as the flowering cycle wears on. You’ll start to see more leaves, more branches, and more buds forming. In some instances, the plant will take the shape of a Christmas tree, with the bottom leaves fanning out and the top leaves sort of rising in a conical shape. The female plants will produce the nice, sticky, THC-laden buds that you will later use for smoking. If you want the THC to be at its most potent, then you don’t want the female plants to be fertilized by the male pollen. You can avoid this by determining the sex as soon as possible, and getting rid of the males so that they don’t pollinate the females. Females that have not been fertilized produce buds that are referred to as “sinsemilla” (or, “without seed” in Spanish).

The flowering process generally takes about 1 to 2 months. You will know that the plant is ready to harvest because the pistils will swell up and start to change colors. You may also start to notice a considerable increase in THC production on or around the buds. THC (short for tetrahydrocannabinol) is a sticky, almost crystalline substance that starts to form around bud clusters on marijuana plants. In terms of biology, THC is used as a mild, natural pest deterrent to keep any bugs away from the flowering plant. As far as human usage goes, THC has considerable psychoactive properties that make it interesting to smoke or ingest.

An unfertilized female plant produces more THC than any other variety of plant simply because it focuses more of its attention on growth rather than reproduction. A fertilized female plant has to focus on seed production and, thus, gives less primacy to producing THC. The substance can be found virtually everywhere on the plant but is most prevalent at the buds. Males also produce THC, but at a much smaller volume than the female plants do.

If you want start growing please download my free grow guide and order some high quality marijuana seeds at this link here. We ship seeds to the US, CA and many other countries. All customers get 24/7 grow support.

Source: ILoveGrowingMarijuana.Com



About Author

Robert Bergman is a master marijuana grower. Robert Bergman is the author of 'Marijuana Plant Care' and 'The Marijuana Grow Bible'.


  1. I have a hash plant clone I got it at 5 inches it’s about 3ft tall and two feet wide and started budding like less then a month ago in sunny Cali also I have a white rhino og seed plant it’s budding but it didn’t grow wide just tall my friend thinks I should ripe off the top flower what should I do and h ow long until I could smoke

  2. budbud, yup, 12 weeks of blooming, average is often 5-10 weeks and if in doubt, read up on much of it in The Marijuana Grower’s Guide circa 1992 (Frank and Rosenthal). It isn’t the God given rule but depending on temps. indoors or out, the bloom phase can take varying amounts of time and I know a few people who actually hit 14 weeks. Did you know that an un- (cough)touched female can grow for a few years depending on how you handled it if males were found to be in the garden and taken out real early? Now THC might be nil by then BUT it is possible to have varying results depending on who grows it and how they grow it. Fertilizers are often key in knowing how to slow down or speed up growth and such a thing would be great to know if the outdoor season turns out to be less than stellar during some growing years. P.S. for a fruit such as a tomato and growing each successive year from seeds from that year’s tomatoes and so on, I also know people who have tomato plants that are how would you say it-“relatives of their first plant almost 20 years ago.” So, 20 years ago you bought a tomato plant and at the end of each season you harvested some seeds, grew your next year’s crop from them and kept that cycle going for 20 years? Are you aware of how crazy that might be since eventually the tomato genes (?) are so buggered up? Well, this same thing can happen either good or bad when using seeds from a plant or two you allowed to be pollinated and every year doing it as such. Probably a lot of oddball relatives or something like a warped family, wouldn’t you say? The moral of all this is that scientists have worked on such things for many decades, some growers have different and successful results and most of what we know or read about, are just guidelines or a general rule. Some state that many plants can hit heights of 14 feet, the only thing I ever grew to be just about that was a sunflower plant and the head weighed about 6 pounds. The average for an indoor homegrown pot plant might be about 6 feet or so and it also dpends on when you pinch and how many times during the growth phase. Mine is about 6 times at various places in 3-4 months and it turns out to be a pretty impressive trunk that is capable of sustaining some nice long bud phases

  3. Okay I’ve been growing since February outside and I’m wondering when they are gonna start to bud?

  4. jaques i never heard of a plant that his 12 week of budding. that long here in canada we think 9 weeks is long lol. i got some blueberry going right now

  5. P.S. total darkness isn’t absolutely necessary depending on how long you were running the 24 hour lights-often if you grow for about 5 months at that rate and then cut back on the lights (even at 14 on and 8 off), the plants WILL react quickly enough. It’s just a general rule of thumb to not hit them with bright shots of light when they are sleeping because if that was actually a serious issue then outdoor lighting (moonlight, neighbours’ yard lights etc.) would never allow any plants to rest and move on to their next phase(s). Many people grow vegetable gardens and have their yards lit up at night and those plants grow too. Cannabis reacts pretty quickly to changes in their light cycles and most people tend to light for 20 hours or so right from the seedling stage, 4 hours either way isn’t that big of an issue and although they can handle light for 24hrs., it isn’t natural to do so. You’ll find that if you give them a rest during their veg. stage, they build up better, stronger trunks and can then handle the heavier buds-trunks should be wood-like and when cut open, have a nice tube-like channel throughout

  6. some can trigger in about 4 days if you were using lights for 24 hrs./day and then cut to 12/12. Often enough though, it usually takes about 2 weeks, then flowering runs anywhere from 2-12 weeks.

  7. how long does it take for the plant to start flowering once you start the 12 on 12 off?

  8. Thank u the stuff i was readind was very helpful i just hope everythings gonna wprk out for me do u have a vadalog u can send me 200 Somerset ave Winthrop mass 02152 thank u kenn

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  10. Sticky Fingers on

    That is a long time, I would be interested to know how big and wide his plants are his final dry yield? I have heard of people using those led bulbs, I know they have to be very close to the plants for good penetration. I’m sure he is using the 2700k to get decent flowering since they only come in 2700k and 5000k, the latter is good for vegetative growth. I have read some people are getting 1 Gram per watt using these. Thanks and keep us updated, just add to this thread when you have his finished weight. Thanks :}

  11. i think it would be because auto strains are a combo of ruderalis with indica and/or sativa. under his 24-hour light regimen, the genes of the latter two I mentioned make the plants want to “veg” o btw clear trichs are good. amber indicates degredation of the cannabinoids.

  12. I know someone who’s growing 2 – Sensi Northern Lights auto’s in 24/0 light – and it’s been over 4 months (over 120 days) and still no amber on all the buds. He’s started harvesting mature buds (30% or greater amber) while leaving clear to cloudy till they mature. Buds look great, plant is healthy, buds continue to fatten up. His lighting is only 8-13W LED’s (104w) from Lowes. This seams like a ridiculously long season. What do you think?

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