When to Start Flowering Cannabis

The flowering stage of cannabis growth (depending on strain) usually takes place from 8 to 11 weeks. The cannabis growth cycle consists of four stages: germination (3 to 10 days), seedling (2 to 3 weeks), vegetative (3 to 16 weeks) and finally culminates in flowering (6 to 12 weeks). Many new growers are unsure of the best time to initiate flowering. Understandably so, deciding when to flower cannabis and transition your plants from the vegetative to flowering stage is an important decision. Flowering too soon results in a smaller overall harvest and too late could mean burned buds.

When you think about it, everything about cannabis makes it a strange and unique plant. Not only is cannabis part of the rare 7 percent of plant species with male and female plants, but it also has both a vegetative and flowering stage of growth! Knowing when to start flowering cannabis depends on several factors: age, height relative to your growing setup, strain and more. Ultimately, no two grows are the same, and these techniques are more of a guideline than a hard rule. When you decide to start flowering cannabis is up to you. In general, if you’re looking for a larger yield, wait and start flowering later. For a quicker harvest, start flowering sooner.

With that said, an important factor to consider before switching to flowering is the actual health of the plant. If the plant is suffering, switching to flowering isn’t going to improve things or produce quality flowers, for that matter. The primary purpose of the vegetative cycle is to build robust vegetation that will support plants as they flower. Deal with any disease, curling leaves and plant health issues before flowering. If your plants are in pretty dire straits, consider cutting your losses rather than trying to force flowers out of them. It’s easier to try again from fresh plants.

Finally, we’ll go over the three flowering phases and optimal light cycles for flowering to help you decide when to start flowering your cannabis plants.

The Four Flowering Stages

As previously mentioned, flowering is the final stage of cannabis growth. It’s also the most rewarding when your work is actualized in the literal crowning of resinous buds. Most strains will flower within 8 to 9 weeks, but some (typically sativas) can take longer. Consider the flowering period to be anywhere from 7 to 14 weeks.

Seasonal shifts as daylight decreases from summer to autumn naturally initiate the flowering process in cannabis. For indoor plants, the process is triggered by reducing the amount of light it receives, usually down to 12 hours. This is called a 12-12 cycle — 12 hours under the light, 12 hours of dark. On average, 2 to 4 weeks in vegetation is sufficient before initiating flowering.

Pre-flower phase (week 1-3)

In the pre-flower phase, your girls will start to develop pistils (small white hairs). As soon as the pre-flower phase begins, switch to the 12-12 light cycle. Keep in mind that your plant (depending on strain) will still likely undergo significant growth beyond these early weeks of flowering. Pure sativas especially can reach final heights of 6 feet and beyond. First-time growers should steer clear of pure sativas, especially if growing indoors.

Early flowering (week 4-5)

The pistils will continue to elongate and begin to look like rather spiny balls. Make sure your daytime temperatures are around 23C at this point. You’ll also want to start trimming your plants regularly. Trimming allows the plant to focus on flowering and allows light to reach the bud sites easier. As the plant continues to progress through the flowering stages, it’s normal for more leaves to start dying as she focuses on her buds. Prune those to ensure a healthy harvest.

Peak flowering (week 6 and on)

This is the point where you’ll see the unmistakable colourful calyxes on your plants. Things are starting to get hot and heavy! Not literally, though. Bud growth peaks at this phase. As your buds get heavier, consider supporting your stems if you see signs of strain. Also, you should be keeping humidity at a stable 45 percent to prevent bud rot — it could ruin your entire harvest.

Final flowering and ripening (week 7 and on)

In the final stage of flowering, the buds will take on that thick, sticky coat of trichomes you know and love. Those white pistils will change colour from white to amber and are a good indicator of when to harvest.


  • Know your strain! Height is important in determining how much room you will need for the final height of your plants.
  • Ensure regular trimming to maintain plant health and focus on bud production.
  • Don’t spend a lot of time and effort nursing sick plants back to health in order to flower them, it’s better to throw in the towel and try again.
  • Pay attention to light and humidity. Switch to a 12-12 cycle in the pre-flower phase and keep humidity no higher than 45 percent to prevent bud rot.
  • The full flowering period — depending on strain — can take anywhere from 7 to 14 weeks.

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