The Cannabis Growth Cycle
Each stage has a different plant. Different needs. Different job.
Educational use only. Cannabis cultivation is subject to federal, state/provincial, and local laws. Verify your local laws before proceeding. Nothing here constitutes legal or medical advice. For adults 21+ (18+ in medical jurisdictions).
Cannabis is not the same plant from week one to week twelve. It germinates, establishes, grows explosively, builds flowers, ripens, and then finishes — each phase with distinct physiology, distinct needs, and distinct failure modes. Understanding what the plant is doing biologically at each stage — not just what the checklist says to do — is what separates growers who react to problems from those who prevent them.
Germination (Days 1–7)
The seed contains everything the seedling needs for its first few days of life. Germination is triggered by warmth and moisture. The radicle (primary root) emerges first, followed by the embryonic shoot. Your only job is to provide the right conditions and not interfere.
The paper towel method is the most reliable for most growers: place seeds between damp (not soaking) paper towels, seal in a zip-lock bag or between two plates, and keep at 72–80°F (22–27°C). Most viable seeds germinate in 24–72 hours. When the tap root is 0.5–1cm long and white, transplant gently to your seedling medium.
Common germination failures: too cold (below 68°F/20°C, germination stalls or fails), too wet (seeds rot), or planting too deep (more than 1–2cm deep). Seeds do not require light to germinate — introduce light only after the seedling emerges.
Tip
Soaking seeds in plain water or a diluted hydrogen peroxide solution (1%) for 12–24 hours before germination softens the seed shell and improves germination rates on older or hard-shelled seeds.
Seedling Stage (Weeks 1–3)
The seedling stage begins when the cotyledons (first round leaves) open and ends when the plant has 4–6 nodes with true fan leaves fully developed. This is the most delicate phase — the root system is minimal, the plant cannot handle environmental stress, and overwatering is the primary risk.
Seedlings do not need nutrients for the first 10–14 days in quality seedling medium — the cotyledons contain stored nutrients. Light feed can begin once the first set of true fan leaves is fully developed. Keep lights at low intensity or elevated height — seedlings are easily bleached by strong light.
Signs of a healthy seedling: deep green cotyledons, tight internodal spacing, thick stem relative to plant height. Etiolation (long, stretched stems reaching for light) indicates insufficient light intensity or an excessively warm environment.
Seedling stage environment targets
| Parameter | Target Range | Notes |
|---|---|---|
| Temperature | 72–80°F (22–27°C) | Warm but not hot; cold stunts seedlings significantly |
| Humidity | 65–75% RH | High humidity reduces transpiration demand on underdeveloped roots |
| Light | 18h/6h or 20h/4h | Low to medium intensity; seedlings cannot use high PPFD |
| Watering | Light, infrequent | Small pot dries fast; bottom watering reduces stem rot risk |
| Nutrients | None for 10–14 days | Cotyledons supply initial nutrition |
Vegetative Stage (Weeks 3–8+ depending on desired size)
The vegetative stage is about building structure. Every leaf, every internode, every branch developed now becomes a flowering site later. A plant with 50 nodes in veg has the potential for 50 bud sites in flower. A plant rushed into flower at 3 nodes will never reach that potential regardless of how well flower is managed.
This is when most training takes place. LST, topping, FIMing, and SCROG setup all happen in veg. The plant recovers quickly from high-stress training at this stage and has time to redirect its energy before flower.
Nutrient demand is high and nitrogen-forward in veg. Maintain good VPD (0.8–1.2 kPa), strong light (18/6 photoperiod for photoperiods, or full cycle for autos), and allow the root zone to develop fully before flipping.
The vegetative period is flexible — you control how long it runs (for photoperiod strains) by the light schedule. Longer veg = bigger plant = higher potential yield, up to the limits of your space. Most indoor growers run 4–8 weeks of veg depending on space, strain, and training style.
Pre-flower and the stretch (Weeks 1–3 of flower)
When you flip to 12/12 (for photoperiod strains), the plant does not immediately start building buds. For the first 1–2 weeks, it continues vegetative growth while its internal hormone system transitions. This transition ends with the appearance of pre-flowers — small pistils (white hairs) at each node, confirming sex.
Following pre-flower is the stretch: a rapid period of vertical and lateral growth that typically doubles or triples plant height. Indica-dominant strains stretch moderately (50–75%); sativa-dominant strains can triple or more. Plan for this in your tent. A plant that fills the vertical space during veg will hit the light during the stretch.
Continue light training (LST, tucking SCROG) during the first 2–3 weeks of flower. Stop all high-stress training once flower sites are actively forming. Defoliation and lollipopping are typically done at week 2–3 of flower when structure is clear.
Flowering (Weeks 3–8+)
True flowering begins after the stretch settles. Calyxes stack, pistils proliferate, and buds begin to bulk. This is when terpene development begins and resin production accelerates.
Nutrient profile shifts in flower: reduce nitrogen progressively from the stretch onward, increase phosphorus and potassium. VPD can push slightly higher (1.2–1.6 kPa) to drive transpiration and nutrient uptake into the building buds. Many growers add a PK-boost supplement in mid-flower (weeks 4–6).
Mid-flower (weeks 4–6 for most strains) is when buds are bulking most rapidly. This is the heaviest feeding window and when most nutrient deficiencies appear if the program is off. Watch for signs of calcium deficiency (brown spots on new growth), phosphorus deficiency (dark or purple leaves), and nutrient burn (brown leaf tips).
Late flower and ripening (Weeks 7–harvest)
Growth slows. Bud density increases. Pistils begin to change color from white to orange and brown. Trichomes continue developing and begin to transition from clear to cloudy to amber.
Begin reducing nitrogen at this point if you have not already. Some growers perform a "flush" with plain water in the final 1–2 weeks, though the science on whether this meaningfully affects taste is contested. What is established: continuing high nitrogen into the final weeks delays maturation and reduces terpene development.
Monitor trichomes closely in the final 2 weeks. The harvest window for most strains is 1–2 weeks wide. Within that window, earlier (more cloudy, less amber) produces a more cerebral, energetic effect; later (more amber) produces a heavier, more sedating effect. Pull when the profile matches your goals.
Warning
Mold risk peaks in late flower. Dense buds with poor internal airflow combined with high humidity are the primary risk factor. In the final weeks, push humidity below 50% (target 45–50% RH), increase airflow through the canopy, and inspect bud sites daily for any soft spots, unusual coloring, or visible mold growth. Botrytis (bud rot) spreads rapidly and invisibly until it has destroyed significant material.