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WEEK 1–8◆PLANT AGE◆LIFE CYCLE◆SPROUT◆VEGETATIVE PHASE◆FLOWERING◆CANNABUBEN◆WEEK 1–8◆PLANT AGE◆LIFE CYCLE◆SPROUT◆VEGETATIVE PHASE◆FLOWERING◆CANNABUBEN◆

Botanical information 2026

Cannabis plant week 1–8

What does a cannabis plant look like at 1, 2, 3 or 4 weeks? Typical height, number of leaves and life cycle stages of the plant — explained week by week, for purely informational and botanical purposes.

By Cannabuben RedaktionLast updated:
8
Growth weeks
8
Frequently asked questions
May 2026
Updated

Legal notice — France

In France, domestic cultivation of cannabis (containing THC) is prohibited by law. This page presents the botanical life cycle of the plant for purely informational and educational purposes. It is not a home cultivation guide for France and this content does not encourage illegal cultivation in any way.

Key takeaways

  • The life cycle of a cannabis plant is divided into three phases: sprout (weeks 1–2), vegetative phase (weeks 3–8+) and flowering.
  • After 1 week, a sprout is 2–5 cm; after 2 weeks, 5–12 cm; after 3 weeks, 10–20 cm; after 4 weeks, 20–40 cm.
  • Flowering is triggered indoors by the 12/12 light cycle and, outdoors, by the natural shortening of days from July/August.
  • This page is purely informational and botanical: in France, domestic cultivation of cannabis (THC) is prohibited by law.

The growth of a cannabis plant is generally divided into three phases: sprout (weeks 1–2), vegetative phase (weeks 3–8+) and flowering. Indoors, the light cycle determines the transition; outdoors, it is the season that commands it. This page describes, week by week and for botanical purposes, what characterizes each stage of the plant's life cycle. Reminder: in France, cannabis (THC) cultivation is prohibited.

The cycle week by week

01

Cannabis plant at 1 week (sprout)

Week 1 — sprout

Typical height2–5 cm
LeavesCotyledons + 1st pair of leaves
Light250–400 µmol/m²/s · 18/6 h
NutrientsNo fertilizer — the substrate is sufficient
Characteristics

Maintain regular humidity, temperature 20–25 °C, high humidity (60–70% RH). No too strong direct light.

Common difficulties

Overwatering → damping off. Substrate too dry → the sprout becomes etiolated.

02

Cannabis plant at 2 weeks (sprout)

Week 2 — start of vegetation

Typical height5–12 cm
Leaves2–3 pairs of leaves (3–5 leaflets)
Light400–600 µmol/m²/s · 18/6 h
NutrientsOptional: very weak nitrogen solution (¼ dose)
Characteristics

Increase lighting. Check LED/HPS distance. pH 6.0–7.0 (soil). First pest inspection.

Common difficulties

Etiolation (stretching towards the light) → move the lamp closer. Light green leaves → beginning of nitrogen deficiency.

03

Cannabis plant at 3 weeks

Week 3 — active vegetation

Typical height10–20 cm
Leaves3–5 pairs of leaves (5–7 leaflets)
Light600–800 µmol/m²/s · 18/6 h
NutrientsStart of nitrogen-rich vegetative nutrition (half dose)
Characteristics

First LST possible. Control ventilation (20–25 °C, 50–60% RH). Adjust watering intervals.

Common difficulties

Yellow lower leaves → nitrogen deficiency. Curled leaves → heat stress or excess nutrients. White spots → spider mites.

04

Cannabis plant at 4 weeks

Week 4 — growth spurt

Typical height20–40 cm
Leaves5–7 pairs of leaves (5–9 leaflets)
Light800–1000 µmol/m²/s · 18/6 h
NutrientsComplete vegetative nutrition — N:P:K approx. 3:1:2
Characteristics

Intensify LST or set up a SCROG net. Control height (lamp distance min. 30–50 cm depending on LED). Optional topping.

Common difficulties

Lack of space → early repotting into a larger pot. Overwatering → root problems. pH drift → nutrient lockout.

05

Cannabis plant at 5 weeks

Week 5 — vegetative plateau

Typical height30–60 cm
Leaves7–9 pairs of leaves, fully developed
Light800–1000 µmol/m²/s · 18/6 h
NutrientsComplete nitrogen nutrition, supplement with calcium and magnesium
Characteristics

Finish training. Inspect for pests (under the leaves!). Check pot size — roots should not circle.

Common difficulties

Calcium spots → supplement with Cal-Mag. Yellow leaf tips → nutrient excess (flushing). Pests under the leaves.

06

Cannabis plant at 6 weeks

Week 6 — transition

Typical height40–70 cm
LeavesFully developed, first signs of pre-flowering possible
Light800–1000 µmol/m²/s — prepare for 12/12 switch
NutrientsSlightly reduce nitrogen, increase P and K
Characteristics

Last major training. Indoors: plan for flowering switch (12/12). Outdoors: first signs of flowering from August.

Common difficulties

Hermaphroditism in pre-flowering → find the source of stress. Lack of space in the grow room.

07

Cannabis plant at 7–8 weeks

Week 7–8 — entering flowering

Typical height50–80 cm
LeavesFlower buds visible
Light12/12 h (indoors)
NutrientsFlowering fertilizer: rich in P and K, nitrogen greatly reduced
Characteristics

Flowering begins. Monitor stretching during weeks 1 to 3 of flowering. Improve ventilation against mold.

Common difficulties

Too little stretching → more light. Too much stretching → reduce distance. Check sex: pollen sacs = male plants.

08

Cannabis plant at 8+ weeks (flowering)

Week 8+ — flowering phase

Typical height60–100 cm (depending on variety)
LeavesCalyxes swell, trichomes develop
Light12/12 h (indoors) · 800–1000 µmol/m²/s
NutrientsPure flowering fertilizer, last flush 1 to 2 weeks before maturity
Characteristics

Observe trichomes with a magnifying glass (clear → milky → amber). Botanical maturity: 70–90% milky trichomes + 10–30% amber.

Common difficulties

Botrytis (grey mold) → humidity below 45%. Foxtailing → too much light/heat. Maturity reached too early → less developed.

Frequently asked questions — cannabis plant age

What does a cannabis plant look like after 1 week?+
After 1 week, the cannabis plant is a sprout 2 to 5 cm tall. You can see the round cotyledons and the first true pair of leaves with 3 leaflets. Botanically, this phase requires regular humidity, 20 to 25 °C and moderate light — overwatering is the most common mistake at this stage.
What is the height of a cannabis plant after 3 weeks?+
After 3 weeks, in full vegetative phase, a cannabis plant is generally 10 to 20 cm tall with 3 to 5 pairs of leaves. At this stage, the plant consumes the most nitrogen. Yellowing lower leaves may indicate the beginning of a nitrogen deficiency.
What is the height of a cannabis plant after 2 weeks?+
After 2 weeks, a cannabis plant is generally 5 to 10 cm tall. The sprout has developed 1 to 2 true pairs of leaves (with 3 to 5 leaflets). Large differences between varieties are normal — sativa-dominant varieties grow more slender and faster, indica-dominant varieties remain more compact.
What is the height of a cannabis plant after 4 weeks?+
After 4 weeks in the vegetative phase, a cannabis plant typically reaches 20 to 40 cm indoors and has developed 5 to 7 pairs of leaves. From this size, the plant enters vigorous growth of its leaf structure.
When does the flowering phase of the cannabis plant begin?+
Indoors, flowering is triggered by switching to a 12/12 light cycle (12 hours of light, 12 hours of darkness) — usually after 4 to 8 weeks of vegetative phase. Outdoors, the plant naturally flowers from July/August, when the days shorten. Autoflowering varieties flower independently of the light cycle after about 3 to 4 weeks.
Why does a cannabis plant turn yellow in week 3?+
Yellow leaves in week 3 most often indicate a nitrogen (N) deficiency — recognizable by the yellowing of lower/older leaves. The substrate pH also plays a role (6.0 to 7.0 in soil). If the new leaves are yellowing, it may be a nutrient lockout related to pH.
How often does the sprout need water in the first 2 weeks?+
Sprouts need regular humidity — never let them dry out completely, but don't let them sit in water either. General rule: when the top 1 to 2 cm of the substrate are dry, water lightly. Better little and often than rarely and a lot. Overwatering is the most common mistake and leads to root rot.
What is LST (Low Stress Training)?+
LST is a training technique that can start from weeks 3 to 4, when the stem is flexible (10 to 15 cm tall, 3 to 4 pairs of leaves). The main stem is gently bent to the side and secured with wire so that the side shoots receive the same level of light. The stem is never broken — only gently bent.
What is the difference between the sprout stage and the vegetative phase?+
Sprout (weeks 1–2): the plant develops its first true leaves after the cotyledons. Vegetative phase (from week 3): rapid growth, higher nutrient needs. The boundary is gradual — general rule: when the plant has 4 to 5 pairs of leaves, it is in the vegetative phase.
How many leaves does a cannabis plant have after 4 weeks?+
After 4 weeks, a cannabis plant generally has 5 to 7 pairs of leaves each with 5 to 9 leaflets — that's 35 to 70 individual leaflets. Indica varieties have wider and darker leaves; sativa varieties have narrower and lighter leaves. Autoflowering varieties may develop their leaves faster.

To go further

Complete guide

Cannabis

Botanical basics — from sprout to plant maturity.

Nutrients

Plant nutrition

Organic or mineral — which nutrients at which growth phase.

Substrate

The right substrate

Which substrate for sprout, vegetation, and flowering — comparison.