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 autoflowering variety, then 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.

Male and Female Marijuana Flower
Male and Female Marijuana Flower – Image powered by Honestmarijuana.com

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).

Pollinated Bud
Pollinated Bud – Image powered by Stuffstonerslike.com

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 seeds at this link here. We ship seeds all over the US. All customers get 24/7 grow support.


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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 led 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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    31 comments on “When Do Marijuana Plants Start To Flower”

    1. Pamie,

      A male is predisposed to be a male and is useless overall. If you are making an infused oil or CBD oil, then the male may be of use. Otherwise there is no worthwhile % of THC. Cull all males unless you are using them for medicine. One pollen flower can ruin your grow by pollinating strong females.

    2. All weeds plants, both male and female can be smoked. Males, however, don’t have a large amount of THX. But, from all of the material I have read and researched, I believe that the statement above is true.

      • Melissa,

        I would not want to smoke male cannabis plants. IN fact; Smoking anything is unhealthy. Smoking males which would require much more organic material to be smoked would not be a sensible alternative.

        We also must mention that the time and effort to raise a male to maturity would be a waste of money and possibly cause the spread of pollen to occur in the females, thereby ruining the whole crop.

        I advise you rethink smoking male plants. At least male cannabis plants

        • I heard one can “castrate” the males instead of leaving them for dead. Has anyone done this before? Male leaves must be good for something?

    3. I know it’s January and I know it’s cold, I’ve been growing my two plants for the past 2 months and they are only 1 foot tall. How do I know whether I have a male or a female . They already smell like bud they just aren’t growing fast enough

      • The plant has to be in flower cycle in order to show sex. Usually an 11-13 hour dark period will cause plant to flower and within 2 weeks generally, pre-flowers will be generated and you can tell the sex.

        I suggest you join us at: support.ilovegrowingmarijuana.com and allow our great community and staff to help you learn to grow successfully. All you need as far as information is right there in the forum. Happy growing

    4. It’s coming up on the end of August and my outdoor plants are still not budding. Can anybody tell me what’s up with them?

    5. hi i am new here , i live on the oregon coast as soon as i started to see the litle buds forming i put black garbage bags over my plants for 12/12 light and dark cycles , why are my leaves turning brown

    6. I have a plant that just popped up in my yard and its about 11 feet tall. I have no clue what to do with it and if it is one that the buds can be smoked or not. The information above really was not helpful to me. where can i get more info on how to tell if my plant is just a plant or if it will be a producer of smoking buds?

      • Dottie,

        You would be well served to join our support forum at ilovegrowingmarijuana.com

        We can help you much better in an open forum setting. I would love to see you post a picture there. Peace

    7. Mine is a indoor it 10 feet high I can’t get it to flower it just keep growing more leaves help what I’m I doing wrong

      • Kathleen Underwood,

        Flowering occurs when the light photo period allows for uninterrupted 12 hours or more of a dark period every day

    8. hi, I have a questions…. my lovely ladies have been in vegetation for 8 weeks and are between 3-4 feet tall… are they ready to go into flowering stage?… and do I need to add any type of nutrients in flowering stage?

    9. Where is the place to send info to get grow book. great read so far. Jp.Goodwin 206N.HIGH Ave. Covington, Virginia 24426

    10. Hola .
      Quiciera recibir ofertas y promociones de diferentes especies de CAnabis.
      Desde ya muchas gracias

    11. In growing outdoors it would be quite helpful if you could give flowering dates in relation to latitude (daylight hours). In the north this will make all the difference between success and failure. I am just below 49 and am interested in Shiva. My plants have to be mature and out of the ground by the first week in October. Your help please.

      • My plant been in the ground since May 23rd and their still vegging and growing rapidly. Why it’s not budding?

        • Kathy,

          There are a lot of questions. My answer is the same to you. Join our forum and let the staff and members guide you to a successful grow.

          This is not the format for helping you with the blind issues you present. Will be happy to help you learn to grow in the IL:GM forum 🙂

        • Ricky,

          It is hard to say what is going on with you plant. It might not be budding due to extreme heat. Who knows. Best thing to do is; Join our forum and once you have looked around and made some posts, you can show us a picture of the plant and we can guide you. Friendly forum with many great folks willing to share expert grow knowledge.

        • I covered my plants for 48 hrs dark and about ome week later the most beautiful bidds appeared and lots of them and quit the aroma