The flowering stage of photoperiod cannabis lasts 7 to 11 weeks from the switch to 12 hours of light and 12 hours of darkness, depending on the genetics. Indica-dominant strains are often finished after 7–8 weeks, sativas need 9–11 weeks. Autoflowering strains start flowering on their own in about their 3rd–4th week and are ready to harvest roughly 9 weeks after sowing.
In this guide we go through the flowering stages of weed week by week: what you see on the plant, what climate it needs, what to do in each phase and which mistakes happen most often. Plus: light in flowering, a separate calendar for autoflowers and the flowering times of our own strains.
Starting flowering: 12/12 and pre-flowers
Photoperiod plants flower when the nights get long enough. Indoors, you switch the lighting from 18/6 (vegetative) to 12/12 — 12 hours of light, 12 hours of complete darkness. That day is “day 1” of flowering. Outdoors the sun takes care of it: in the northern hemisphere most strains start flowering from late July to early August, when the days get noticeably shorter.
As early as 1–2 weeks after the switch, sometimes even before, the pre-flowers appear: small calyxes with two white hairs (pistils) form in the leaf nodes. That tells you the plant is female. If small balls without hairs form instead, it is a male — how to tell them apart with certainty is shown in our guide Male vs female cannabis plant. With feminized seeds you can skip this sorting.
Cannabis flowering stage week by week: the overview
The weeks refer to a strain with about 8–9 weeks of flowering. Fast indicas are a week ahead, sativas one to two weeks behind.
| Week | What you see | Climate | To do | Typical mistake |
|---|---|---|---|---|
| 1–3 · Stretch | Plant grows 1.5 to 2 times taller, first white pistils at the shoot tips | 22–26 °C (72–79 °F), 50–60% RH | last training (LST), thin out lower shoots, adjust the light | too little headroom planned |
| 4–5 · Bud formation | Pistils cluster into buds, the smell becomes clear | 22–26 °C (72–79 °F), 45–55% RH | carbon filter, air movement, switch to bloom fertilizer | smell underestimated, poor ventilation |
| 6–7 · Bulking | Buds get thick and heavy, trichomes dense, first pistils change colour | 20–25 °C (68–77 °F), 40–50% RH | lower humidity, support branches, check buds for mold | humidity too high → bud rot |
| 8–10 · Ripening | Most pistils orange-brown, trichomes milky to amber, leaves yellowing | 20–24 °C (68–75 °F), 40–45% RH | check trichomes with a loupe, plain water in the last 1–2 weeks | harvesting too early |
Weeks 1–3: Stretch and first pistils
In the first weeks after the switch, the plant shoots up. Indicas grow about 1.5 times taller, sativas can double or triple their height. At the same time, the first white pistils appear at the shoot tips.
- Plan the space: before switching to 12/12, make sure there is enough headroom — the light has to be able to move up with the plant.
- Last chance for training: gently tying shoots down (LST) is still possible. Avoid heavy pruning from week 2, as it stresses the plant.
- Thin out: small shoots in the lower third barely get any light. Removing them directs the energy into the upper buds.
Weeks 4–5: The buds form
Growth in height is now largely complete. The plant puts its energy into the flowers: the clusters of pistils turn into recognisable buds, and the smell increases noticeably.
- Control the smell: by now at the latest, the extractor needs a carbon filter.
- Ventilation: a circulation fan keeps the air between the buds moving and helps prevent mold.
- Nutrients: the plant now needs less nitrogen and more phosphorus and potassium. Switch gradually to a bloom fertilizer and follow the manufacturer’s instructions.
Weeks 6–7: The bulking phase
In the bulking phase the buds gain the most weight. The trichomes get denser, the flowers glisten and the first pistils turn orange. This is when the final yield and quality are decided.
- Lower the humidity: 40–50% RH. Dense buds hold moisture — the main cause of mold. How to spot it early is shown in our guide Bud rot and cannabis mold.
- Support the branches: heavy buds can snap shoots. A net, stakes or plant ties help.
- No more repotting or pruning: any stress now costs yield.
Weeks 8–10: Ripening and harvest time
In the last weeks the plant ripens. Most pistils are orange to brown and have curled in, and older leaves turn yellow because the plant uses up its reserves. That is normal.
- Check the trichomes: with a loupe or a phone microscope. Clear trichomes mean “still too early”, milky ones peak potency, amber ones a heavier, more physical effect.
- Flushing: many growers give only plain water in the last 1–2 weeks so the plant uses up residual nutrients.
- Don’t harvest too early: the last week still adds noticeable weight.
Everything about the right moment and the harvest itself is in our guide When to harvest cannabis — and after that it continues with drying and curing.
Light in the flowering stage
- Strict 12/12: the 12 hours of darkness must be truly dark. Light leaks through gaps, indicator lights or an open tent can stress the plant and lead to hermaphrodites.
- Spectrum: modern full-spectrum LEDs cover both vegetative growth and flowering. Some lights have a dedicated bloom mode with more red.
- Distance: follow the lamp manufacturer’s guidance. Too close leads to bleached, yellow tips (“light stress”), too far to loose, airy buds.
- Outdoors: the more direct sun, the denser the flowers. A sunny spot with rain protection is half the harvest in a short, wet season.
Temperature, humidity and nutrients in flowering
| Phase | Temperature (lights on) | Humidity | Nutrient focus |
|---|---|---|---|
| Early flowering (weeks 1–3) | 22–26 °C (72–79 °F) | 50–60% | transition: still some nitrogen, more phosphorus |
| Mid flowering (weeks 4–7) | 22–26 °C (72–79 °F) | 40–50% | phosphorus and potassium, little nitrogen |
| Late flowering (weeks 8–10) | 20–24 °C (68–75 °F) | 40–45% | reduce fertilizer, finally plain water only |
At night it should not get more than about 5–8 °C (9–14 °F) cooler than during the day. Cooler nights in late flowering can bring out purple colours in some strains. Always follow the manufacturer’s instructions on fertilizer amounts and rather dose a little less — overfeeding is one of the most common mistakes. How much to feed in each flowering week, and how to recognise and fix nutrient burn, is covered in our cannabis feeding schedule.
Autoflower flowering stages: a calendar of their own
Autoflowering strains don’t need a switch to 12/12. They flower according to their internal clock, and you count the weeks from germination. Indoors they usually run under 18/6 or 20/4 throughout.
| Week from germination | Stage | What to watch |
|---|---|---|
| 1–3 | Seedling and short vegetative phase | don’t repot — ideally sow straight into the final pot |
| 3–4 | Pre-flowering | only gentle training, no more topping |
| 4–6 | Stretch and bud formation | raise the light, switch to bloom fertilizer, rather half dose |
| 6–8 | Bulking | lower humidity, check the buds |
| 8–10 | Ripening and harvest | check trichomes, plain water at the end |
Our Auto Northern Lights and Auto Tutankhamon are ready about 63 days after sowing under LED (70 days as standard). More on the principle is explained in our guide Autoflowering seeds explained.
Flowering times of our strains
| Strain | Type | Flowering indoors | Outdoor harvest (northern hemisphere) |
|---|---|---|---|
| Galaxy Fast | Fast, 70% indica | 48 days (as little as 45 under LED) | early, fast-flowering |
| Anesthesia | 90% indica | 48 days under LED | 1st–2nd week of September |
| Northern Lights | 90% indica | 55 days (48 under LED) | early September |
| Anubis | 70% indica | 48 days under LED | 1st–2nd week of September |
| White Widow | 50% indica / 50% sativa | 60 days (53 under LED) | 2nd–4th week of September |
| Tutankhamon | 60% sativa | 60 days (53 under LED) | mid to late September |
| Amnesia Gold | 75% sativa | 65–75 days | 2nd–3rd week of October |
For outdoor growing in a short season — the UK, northern and central Europe, Canada and the northern US — strains with a harvest in early to mid-September are the safest: they are finished before the autumn rain and cold arrive. Even faster are our fast-flowering seeds; how fast versions work is explained in Fast version seeds explained.
Common problems in flowering
| Problem | How to recognise it | What helps |
|---|---|---|
| Light stress | bleached, yellowish tips right under the lamp | raise or dim the light |
| Heat | leaves curl up, buds get loose and “foxtailed” | increase extraction, move the light away, keep the temperature below 28 °C (82 °F) |
| Mold (bud rot) | brown, wilted little leaves in the bud, grey fuzz inside | remove affected parts generously, lower the humidity |
| Nutrient deficiency | leaves already turning strongly yellow in mid-flowering | check fertilizer and pH — slight yellowing towards the end is normal |
| Hermaphrodites | small “bananas” (anthers) between the flowers | close light leaks, avoid stress, remove the anthers |
FAQ: Cannabis flowering stage
How long is the flowering stage of a weed plant?
For photoperiod strains, 7 to 11 weeks from the switch to 12/12. Indica-dominant strains such as Northern Lights are finished after about 48 days under LED, sativas such as Amnesia Gold need 65–75 days. Autoflowers are ready to harvest about 9 weeks after sowing.
When do buds get bigger?
The buds gain the most mass in the bulking phase, around flowering weeks 6 and 7. Before that, from week 4, they form out of the clusters of pistils; afterwards they only ripen.
How do I know my plant is in the flowering stage?
By the first white pistils in the leaf nodes and at the shoot tips, usually 1–2 weeks after the switch to 12/12. At the same time the plant stretches noticeably. Autoflowers do this on their own in their 3rd–4th week.
What happens if you let cannabis flower too long?
The trichomes turn increasingly amber, the effect gets heavier and sleepier, and THC slowly breaks down. The risk of mold also rises. Harvesting a few days later usually does no harm; several weeks later does.
What light does cannabis need in the flowering stage?
12 hours of light and 12 hours of complete darkness. Full-spectrum LEDs work well, and many have a bloom mode with more red. What matters is that no light gets in during the dark period — light leaks can lead to hermaphrodites.
What is the ideal temperature in flowering?
With the lights on about 22–26 °C (72–79 °F), in late flowering 20–24 °C (68–75 °F). Humidity falls from 50–60% at the start to 40–45% at the end, so that no mold forms in the dense buds.
What are the stages of an autoflower?
Counted from germination: seedling and a short vegetative phase in weeks 1–3, pre-flowering in weeks 3–4, stretch and bud formation in weeks 4–6, bulking in weeks 6–8 and ripening and harvest in weeks 8–10. Autoflowers need no switch to 12/12 and stay on 18/6 or 20/4.
What is the flowering time of Northern Lights?
Our Northern Lights flowers for 55 days indoors, or as little as 48 days under LED; outdoors in the northern hemisphere it is ready in early September. Auto Northern Lights is finished 70 days from germination (about 63 days under LED).
Short flowering for a short summer
The shorter the flowering, the safer the harvest — indoors and outdoors. Our fast-flowering strains and autoflowers are bred for exactly that, with a germination guarantee and discreet shipping to the UK, Europe, the USA, Canada and worldwide.
Fast versions of our strains, flowering in as little as 45 days under LED — ideal for short summers and quick indoor runs.
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