The flowering stage is the part of a cannabis plant’s life when it stops putting most of its energy into leaves and stems and starts building flowers. In photoperiod plants the cue is light: once the nights are long enough, which indoors usually means 12 hours of light and 12 hours of darkness, the plant begins forming buds. Autoflowers start on their own as they mature. What you harvest is the inflorescence, a dense cluster of small female flowers wrapped in leafy bracts, with white stigmas and resin glands called trichomes. Over roughly 8 to 12 weeks it passes through stretch, bulking and ripening, and the plant’s feeding and canopy needs change along the way.
What “inflorescence” means on a cannabis plant
In botany, an inflorescence is a group of flowers arranged on one branching system. A single cannabis flower is tiny. What you harvest is the whole cluster. Research on female cannabis shows that short days cause intense branching, and the result is a compound raceme: a main stem carrying many short side stems, each carrying flowers.
A 2024 study described how the dense cluster forms. The shoot tip branches heavily, new leaves get fewer leaflets, and leaf stalks and nodes become very short. The single flowers end up crowded together. That crowding is what makes a bud dense.
The inflorescence matters because that is where the resin is. A 2021 review notes that unpollinated female flowers contain up to 10 times more cannabinoids than the leaves and stems.
The parts of a bud
| Part | What it is | What to look for |
|---|---|---|
| Calyx / bract | The teardrop-shaped green pod around each female flower | Swells during late flowering |
| Pistil / stigma | The two white hairs from each flower; they catch pollen | White at first, later darken |
| Trichome | Tiny resin glands on the surface | Densest on calyxes and bracts |
| Sugar leaves | Small leaves inside the bud | Also carry trichomes |
| Cola | The main bud cluster at the top of a stem | Largest, densest buds |
Growers say calyx; botanical papers usually describe each female flower as sitting in the axil of a bract. Growers also say pistils for the white hairs, while papers call them stigmas. Both pairs of words point to the same thing on the plant. Stalked glandular trichomes are concentrated on the calyxes and bracts and extend onto the sugar leaves. This is why the trim from around the bud is still resinous.
What triggers flowering
Cannabis is a short-day plant. It measures the length of the uninterrupted dark period. Indoors, growers keep plants in vegetative growth under 18 hours of light and 6 hours of darkness, then switch to 12/12. At 12/12, a plant of any size will stretch and flower.
Twelve hours is a convention, not a hard line. In one study of ten drug-type cultivars, flowering started in all of them under every day length up to 14 hours. Another study on hemp found that a difference of only 15 minutes in day length changed flowering in some cultivars. The exact threshold is genetic.
The dark period must stay dark. A grow book warns that even a flashlight during the night can disrupt the flowering signal and push the plant back towards vegetative growth. Check your room for leaks from inside the dark space.
Two things are often confused with the start of flowering:
- Pre-flowers. These are the first small flowers a plant makes, and they are the earliest visible sign of its sex. Researchers found that these single flowers appear at the nodes even under long days, as the plant ages. A few white hairs during veg show that the plant is mature, not that bud production has started.
- Autoflowers. These are photoperiod-insensitive. They flower on their own schedule and do not need a switch to 12/12.
The flowering stages
Timing varies with genetics. Indica-leaning plants usually finish sooner than sativa-leaning ones. One grow handbook gives 60 to 100 days of flowering depending on the strain. The stages below follow a common grower breakdown.
1. Transition and stretch
After the switch to 12/12, visible flowering usually begins within 7 to 14 days. At the same time, the plant grows fast in height. This is the flowering stretch. It mostly happens in the first two weeks, and sativa types can end up two or three times taller than at the switch.
Lab work shows the same pattern. Under short days, internodes that were already forming elongated quickly between day 5 and day 10. After that, new internodes stopped elongating and a condensed inflorescence formed. Researchers define visible flowering as at least three pairs of stigmas at the top of the main shoot.
Stretch control is its own topic. The key point here: plan your height before the switch, because the plant is not finished growing when you flip.
2. Bud set
Around two weeks into 12/12, growth slows and the first real flower clusters appear at the tops and at the nodes. Vegetative growth of indoor cannabis almost stops after four to five weeks under a 12-hour photoperiod. From then on, energy goes mainly into flowers.
3. Bulking
Now the plant stops getting taller but gets heavier. Buds grow larger, denser and more fragrant. New flowers keep appearing in waves, calyxes swell, and resin covers the clusters. Some pistils turn yellow-brown, and a few lower leaves turn yellow. This yellowing is normal at this stage.
4. Ripening
Buds lengthen less and firm up. Most pistils have turned brown. Under strong light the trichomes glitter. This is the harvest window. Harvest timing is best judged by looking at trichomes with magnification, which is covered in a separate article. Pistil colour alone is only a rough guide.
5. Senescence
If you wait too long, flowers stop developing, all pistils are brown, and the leaves yellow and fall.
How to tell which stage you are in
- Stretch: fast height gain, spacing between nodes still normal, few white hairs.
- Bud set: height gain slows, white hairs gather at tops and nodes.
- Bulking: no more height, buds thicken each week, strong smell.
- Ripening: buds firm, most hairs darkened, trichomes shiny and dense.
Common mistakes
- Counting pre-flowers as flowering. Solitary flowers appear in veg too. Count flowering from the day you switched the lights.
- Light leaks. Any light that reaches the leaves during the dark period can slow or disrupt flowering.
- Flipping too late in a small space. Forgetting the stretch leaves plants jammed against the lights.
- High humidity in dense buds. Grow books advise keeping humidity low during flowering and warn that frequent spraying at this stage leads to mould and bud rot. This matters even more in humid tropical air.
- Going back to long days. Research shows the inflorescence needs continuous short days. Return a flowering plant to long days and the bud cluster starts to fall apart into leafy growth.
Outdoors in the tropics
Near the equator, days stay short compared with a temperate summer. Researchers working on hemp point out that these short day lengths reduce vegetative growth and trigger early flowering. Many photoperiod plants set outdoors in Southeast Asia will therefore start flowering while still small. Choose genetics and timing with that in mind.