Cannabis Flowering Stage Week by Week: Full Guide

This guide is written for adults. Home cultivation is an adult-only activity, and the timelines below assume you're growing in a jurisdiction where it's permitted.

The cannabis flowering stage week by week is a structured 8–12 week cycle that takes your plant from the 12/12 flip through stretch, pistils, bulking and ripening to a harvestable crop. For photoperiod cannabis, it begins when you flip the light cycle to 12 hours on / 12 hours off. For autoflowers, it starts on the plant's own clock — usually around week 4 from seed. Most photoperiod genetics finish in 8–10 weeks of flower; some sativa-leaning lines push 12+. What changes week to week isn't just the buds — it's the environment you need to hold, the nutrients the plant wants, and the problems most likely to ruin your crop.

Educational content only. This guide does not constitute medical, horticultural, or formal advice. Consult a qualified professional before making decisions that affect your health or circumstances.

Before the flip: what week 0 looks like

Week 0 is the final 5–7 days of veg, when you lock in plant structure before triggering flower. You shouldn't flip to 12/12 until the plant has the structural frame you want. In our own tent testing over a decade, plants roughly double in height during the stretch — a 40cm plant at flip becomes ~80cm by week 3. If your tent is 120cm tall with a light hanging at the top, flip when the canopy is around 30–40cm, not 70cm. Any final topping, LST, or defoliation should happen 5–7 days before the flip so the plant can recover.

AZARIUS · Before the flip: what week 0 looks like

Target environment going in: 24–26°C lights-on, 60–65% RH, VPD ~1.0 kPa. PPFD in late veg sits around 400–600 µmol/m²/s (Chandra et al., 2015).

Week-by-week environmental targets

The table below summarises the core targets growers ask about most — use it as a quick reference when you set up climate controllers or buy a new grow tent kit.

AZARIUS · Week-by-week environmental targets

Week 1 — The transition

Week 1 is a hormonal handover: the plant is still in veg mode visually but reading the shorter photoperiod. Flip day 1 to day 7. You'll see accelerated vertical growth (the "stretch" begins), lighter green new leaves, and no flowers. Sex shows near the end of the week on regular seeds as pre-flowers in the nodes; feminised seeds are effectively all female (breeder documentation from Dutch Passion, Royal Queen Seeds, and Sensi Seeds all report >99% female expression).

AZARIUS · Week 1 — The transition

• Light: 12/12, PPFD 500–700 µmol/m²/s
• VPD: 1.0–1.2 kPa (around 25°C, 60% RH)
• Feed: still a veg-leaning ratio, higher N, EC 1.4–1.8 in coco
• Watch: stretch rate — if you're running out of headroom, start LST now

Week 2 — Pistils appear

Week 2 is when the first white pistils emerge at the bud sites, signalling flower initiation is locked in. They show on the main cola first, then laterals. Stretch continues aggressively — this is often the fastest vertical growth the plant will ever do. Start rotating branches and tucking leaves to keep light on the lower sites.

AZARIUS · Week 2 — Pistils appear

• Feed: transition feed — drop N slightly, bring P and K up. EC 1.6–2.0
• pH: 5.8–6.2 in coco/hydro, 6.2–6.8 in soil
• RH: 55–60%; you want it dropping steadily from here on

Week 3 — Stretch ends, bud sites define

Week 3 marks the end of vertical growth and the definition of every bud site you'll harvest. Pistil clusters thicken at every node. This is the last clean window for any plant training — after this, woody stems won't bend without snapping. If you're running a SCROG net, get everything tucked under it by the end of this week.

AZARIUS · Week 3 — Stretch ends, bud sites define

Feed: full bloom ratio now. Calcium and magnesium demand climbs — if you're in coco or RO water, Cal-Mag is doing real work. Early deficiencies usually show on new growth as pale, twisted leaves.

Week 4 — Bulking begins

Week 4 is where buds put on visible mass for the first time, and trichome frost appears on sugar leaves and calyxes. The plant's calorie demand peaks around now — this is where underfeeding shows as yellowing lower leaves, and overfeeding shows as clawed, dark-green fan leaves with burnt tips.

AZARIUS · Week 4 — Bulking begins

• PPFD: 700–900 µmol/m²/s (push to 1,000+ only with CO2 supplementation)
• VPD: 1.2–1.4 kPa — bump it by lowering RH to 50–55%
• Feed: peak bloom, EC 2.0–2.4 in coco

Weeks 5–6 — Fattening and smell

Weeks 5–6 are when buds stack vertically, fill out sideways, and resin production ramps hard enough that odour control becomes non-negotiable. Your tent will smell noticeably stronger by the end of week 5, which is when a good carbon filter stops being optional — order one before you need it, not after. Trichomes are mostly clear, transitioning to cloudy on early genetics.

AZARIUS · Weeks 5–6 — Fattening and smell

This is the highest-risk window for powdery mildew if RH climbs, and the start of the bud-rot (botrytis) risk window on dense-flowered genetics. Keep airflow moving through the canopy — not blasting directly at buds, but constant movement. Any defoliation here should be conservative: a few large fans blocking bud sites, not a schwazzing pass (the yield evidence on heavy mid-flower defoliation is contested and easy to get wrong).

Weeks 7–8 — Ripening

Weeks 7–8 are the ripening window: pistils brown and curl, trichomes shift from clear to cloudy, and mobile nutrients retreat from fan leaves into flowers. The first amber heads appear on early-finishing genetics. Fan leaves begin yellowing — this is normal and desired, not a deficiency.

AZARIUS · Weeks 7–8 — Ripening

• Feed: drop EC to 1.2–1.6. If you flush, do it now — whether flushing meaningfully improves cure quality is genuinely disputed in the horticulture literature, but most growers taper nutrients in the final 1–2 weeks regardless
• RH: 45–50% — lower end of the range, especially overnight
• Temperature: drop night temps to ~18–20°C to deepen colour on anthocyanin-expressive genetics

Weeks 9–10 — Harvest window

Weeks 9–10 are the harvest window for most indica-leaning and hybrid photoperiod genetics, with sativa-dominant lines pushing later. Sativa-dominant lines (Haze types, some landrace sativas) can push to week 12 or beyond. The only reliable harvest indicator is trichome colour under a 60x+ jeweller's loupe or USB microscope — if you don't own one yet, get one before week 6, not after. Compared to judging by pistil colour or the calendar, trichome reading is the only method that survives contact with real genetics.

AZARIUS · Weeks 9–10 — Harvest window

• Mostly cloudy + ~10–20% amber: classic harvest window
• All cloudy, no amber: earlier, clearer effect profile
• 30%+ amber: later, more sedating profile

Cut in the dark (lights-off or pre-dawn), hang whole plants or large branches in a space at 18–20°C and 55–60% RH. A proper dry takes 10–14 days. Rushing the dry is the single most common way growers ruin an otherwise good harvest.

How autoflowers differ

Autoflowers flower on age rather than photoperiod, compressing the full seed-to-harvest cycle into 9–11 weeks. Autoflower genetics (Cannabis ruderalis crosses) run on an 18/6 or 20/4 light cycle throughout. The weekly progression above still applies — pistils, stretch, bulking, ripening — it's just compressed, and you never flip the light cycle. Because the plant can't recover from stress the way a photoperiod can (no extended veg to regrow), keep training gentle: LST yes, topping late is risky, heavy defoliation no.

AZARIUS · How autoflowers differ

Common week-by-week failures

Most flowering-stage disasters cluster in predictable windows, which means they're also predictable to prevent.

AZARIUS · Common week-by-week failures

• Weeks 1–2: running out of headroom because the stretch was underestimated — burns the canopy on the light
• Weeks 3–4: nutrient burn from running veg-level N into bloom, or Cal-Mag deficiency in coco/RO setups
• Weeks 5–6: powdery mildew and the first botrytis spots on dense colas — almost always an airflow/RH problem
• Weeks 7–8: panicking about normal yellowing and overfeeding, pushing nitrogen back into leaves that should be draining
• Weeks 9–10: harvesting on the calendar instead of the trichomes, or rushing the dry because the tent is needed for the next run

Interaction risks for consumed cannabis (CNS depressants, SSRIs, MAOIs, warfarin) are covered on the cannabinoids hub, not here — this guide is about growing the plant, not consuming it.

Last updated: April 2026