Cannabis Basics

Cannabis Flowering Phase

Cannabis Flowering Phase


The Cannabis Flowering Phase can be triggered at almost any time. It starts when the light cycle is changed to 11-13 hours on, and the rest off. This simulates the seasons of the year, in which plants flower naturally. If you’re growing indoors, it’s nice to have 2 separate areas, one for flowering and one for seedlings/vegetative growth. Once flowering has started, there should be no light interruptions, and a steady schedule is important. A single interruption or unplanned blackout can put off flowering by several days, or even weeks.

The Best Time to Flower Marijuana 

Generally plants are considered old enough to mature when they have reached 12”. Dark periods are required to produce fruit (or bud, in this case) once the cycle has begun. In the Cannabis Flowering Phase schedules should be pretty exact, so I recommend getting a timer and setting your lamps up to go on automatically. If you’re growing outdoors during the summer, you can cover your greenhouse with a blanket during the appropriate times, so that the plants get about 12 hours of light and 12 of dark. The first 2 weeks of the flowering stage are the most essential, and during this period the schedule must be EXACT. After the 2 initial weeks have passed, you can relax the schedule a little bit, but still try to stay on time for the most part.

Outdoor Flowering Cannabis

During the spring and fall, the nights are long enough to trigger the Cannabis Flowering Phase naturally, so no covering is necessary. You can just bring the plants in and out of your house at the appropriate time. In late summer you will only have to force flowering for the initial 2 weeks, and after that the longer nights of fall will do the rest naturally.

Cannabis Flowering Phase Cannabis Flowering Phase

Flowering Marijuana Plants Indoors need scheduled light and high P plant foods. 12 hours on, 12 hours off is good, but 13/11 can increase the flower size. If speed is a priority for you, use longer dark periods towards the end of the flowering cycle, as this will speed up the maturing process. You should know, however, that if you do this, the overall yield will be less.


If you don’t want to grow outside at all, you can grow indoors with a 2-shelf setup. One shelf should have constant light, and be used for seedlings and vegetative growth, while another shelf has 12-13 hours of light, and is used for flowering. Plants started in the constant light will be ready to move to the Cannabis Flowering Phase on/off light shelf within a few weeks, possible up to a month or two. Since plants in the vegetative growth stage are smaller than flowering plants, you should make your flowering shelf significantly larger than the other one. If there isn’t enough space on your flowering shelf, you can take some of the bigger, stronger plants outdoors.


A light curtain is a good idea, ideally one with a reflective surface on one side that reflects light back at the plants. Black vinyl works fine. The curtain should have some sort of rope or tie on the bottom of it, so it can be rolled up and tied while you work on the garden. You should also fasten the curtain to the ground, either with Velcro or something else, so that light doesn’t escape. These curtains are very incognito, and won’t usually be noticed by visitors unless you point it out to them.

Cannabis Flowering Fertilizer

High P level plant foods are good for flowering plants. 5-50-17 is ideal, but 10-20-10 will do the trick. When plants begin flowering, nutrients should be added with each watering, and slowly reduced over time as the plants develop. Many trace elements are necessary for flowering to. If you can, find plant foods that contain the elements already, so you won’t have to buy separate things. Iron is important, and luckily enough most garden/home improvement stores sell fertilizer rich in iron, which is intended to improve the health of lawns. These fertilizers are much cheaper than specialized hydroponic fertilizers, and work just fine. For flowering, use the following solution (per gallon):


1 teaspoon high P plant food (15-30-15 or something better)
½ teaspoon Epsom salts
1 teaspoon Oxygen Plus Plant Food (optional, but highly recommended)
1 teaspoon Trace Element Food (if not contained in plant food)


Remember, the most important part of the flowering phase is to remember that light cycles CANNOT be interrupted. Even small light outbreaks during dark periods halt flower development. This is because the plant releases a hormone that reacts to light. If you need to get in and work on your plants during dark periods, only use a very dim light, and try to be out within 5 minutes. If you need to work for longer than that, you can get a green light. Green lights are sold as nursery safety lights in stores, and they have no negative effect on flowering plants. It’s important to schedule your dark periods when you normally wouldn’t work on your gardens anyways. For instance, a lot of people set their dark times to be around 8pm-8am, so that they can check their plants at night and in the morning before work, but sleep through the majority of the flowering time.


Flowering is the most delicate time for the plants. Don’t spray too often, as plants can mold and rot easily. Also, keep humidity levels down as low as possible during flowering. Flowering begins 1-2 weeks after turning the lights on to 12 hour cycles. When it first starts, look for 2 white hairs coming out of every internode. These hairs are the easiest way to distinguish between male and female plants. Contrary to what a lot of people think, there is no way to tell a female from a male by looking at size of plant, height, or bushiness.


After 3-6 weeks of a steady light cycle, plants will be covered with pistils. Every grow tip on the plant will literally be covered with these small white hairs (pistils). These will be the mature flowers in the future. Once you feel your plants are ready (meaning the plant has enough flowers), you can turn the lights on for 8-10 hours per day. This will speed up the ripening process, and should be ready to harvest after an additional 2-3 weeks. Alternatively, you can simply use a 12/12 cycle throughout the entire flowering process. This will increase overall yield, but take longer. You can also put your plants outside to take advantage of the natural light cycles.


Once the plant has reached its peak of floral growth, it cannot revert back to vegetative growth, so steady light cycles are not necessary. The plant will continue to develop and final flowering will occur regardless of light (as long as there is a decent amount). This is helpful because you can free up some indoor growing space, making room for clones or seedlings.


Watch closely and wait for the hairs to turn orange, red, or brown. Once they have changed colors, or at least about 80% of them have, the flowers are good to harvest. Do not directly touch the buds with your hands, as THC will come off on your fingers. If you must inspect the buds, grab onto the large fan leaves.



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