GROW PLANNING
Cannabis Grow Cycle Planning: Timeline from Germination to Harvest
Successful cannabis cultivation begins with clear planning: What phases does a plant go through? What are the optimal timeframes? What nutrients and light values in each phase? This guide shows you the complete 16-20-week cycle from germination to harvest—with exact EC/pH targets, light schedules and the most common optimization mistakes that professional growers avoid.
The 5 Phases of Cannabis Grow Cycle: Overview and Duration
A cannabis cycle breaks down into 5 biological phases, each with different requirements. Understanding these phases is the foundation for planning and optimization.
| Phase | Duration | Light Cycle | Height Gain | Nutrient Focus | Key Feature |
|---|---|---|---|---|---|
| Germination | 3-7 days | 16-18h | 0-2 cm | None (plain water) | Root emerges, seedling breaks soil |
| Seedling | 7-14 days | 18-20h | 2-10 cm | Weak (EC 0.4-0.6) | First true leaves, root development |
| Vegetative | 28-42 days | 18h Light/6h Dark | 30-50 cm | Stable (EC 1.2-1.4, N-heavy) | Strong height gain, leaf mass buildup |
| Flower | 56-70 days | 12h Light/12h Dark | 20-30 cm (stretch) | K/P Boost (EC 1.4-1.6) | Flower formation and mass buildup |
| Maturation | 14-21 days | 12h/12h (like flower) | None | EC Reduction (1.0-1.2), osmotic finish | Trichome coloring, potency and flavor |
Core Phase Planning Principle: Each phase has a biological goal (root, growth, flowering, maturation). Nutrients, light and climate zones must align with this goal. Giving flower nutrients in week 3 wastes potential. Staying in veg too long only delays harvest. Right phase + right nutrients = consistency and yield.
Germination and Seedling (Weeks 1-2): Light, EC and Substrate Setup
The first phase is delicate yet simple: activate germ energy, start root, stabilize seedling. Mistakes here cost multiple days of growth later.
Germination (Day 1-7)
Start with your chosen germination method: paper towel, water, or direct in substrate. Goal: root (radicle) emerges after 3-7 days. Plant immediately into substrate. Substrate should be pre-buffered and moist (see Coco Buffering Guide). Temperature: 22-25°C, humidity 65-75%.
Light Cycle: Not critical during germination. Some give 16h light; some keep dark. Only switch to 18-20h light once seedling breaks soil (cotyledons visible).
Seedling (Day 8-14)
The germinated seed has broken through and shows first cotyledons (seed leaves). Real growth begins now. Light cycle: 18-20h light / 4-6h dark. PPFD: 150-250 µmol/m²/s (young plants are still sensitive). Distance should be 30-50 cm above the plant.
Seedling Nutrients: First 1-2 weeks can run completely without nutrients—buffered germination substrate is enough. After 1-2 weeks start weak nutrient solution: EC 0.4-0.6. This is about 1/4 of full veg strength. CalMag should be included (2-3 mL/L). pH: 5.8-6.2 (coco).
Watering: Seedlings are sensitive to waterlogging. Substrate should be moist, not wet. Too much water = dilution, root rot, stagnation. Too little = stress and drying out. Rule: pick up pot—if light, water. If heavy, wait.
Vegetative Phase (Weeks 3-6): 18/6 Light Schedule, EC Ramp-up and Training
Veg phase is the growth window. Plants pack on height, leaf mass and roots. This is also your chance for topping and training—before flower locks morphology in place.
Light Cycle and Intensity
Switch to 18h light / 6h dark (or 20/4—some growers prefer it). PPFD should now be 400-600 µmol/m²/s—much higher than seedling stage. Light fixture distance: 30-50 cm depending on LED power. Temperature: 22-25°C (day), 18-22°C (night). Humidity: 55-70%.
Nutrient Ramping in Veg
Week 3-4: EC 1.0-1.2. Week 5-6: EC 1.2-1.4. This is gradual buildup—don't jump to full strength immediately. High EC too early = salt stress and growth inhibition. Gradual increases signal to the plant: growth is okay, nutrients are available. Nutrient focus in veg: nitrogen (N) dominant but balanced K and P. A good veg fertilizer has roughly N:P:K = 2:1:1.5.
Topping and Training
Once plant has 4-5 true leaf pairs (week 3-4) you can top: remove the uppermost growth tip. This promotes bushy growth rather than one main stem. After topping: 3-5 days stress recovery, then bushier growth continues. Alternative to topping: Low Stress Training (LST)—bend branches to sides without cutting. More conservative and also works.
Result Goal: After 6 weeks veg your plant should be 30-50 cm tall with dense foliage and strong root system. Height depends on genetics and setup—indicas are compact, sativas tall.
Flower Initiation and Development (Weeks 7-14): 12/12 Switch, K-Boost and EC Peak
Flower phase is the yield driver. Light signal (12h/12h) triggers hormone production—flowers form. This phase lasts 8-10 weeks depending on strain.
Week 1-2: Flower Initiation and Stretch
First flower week you see pre-flowers—white hairs (pistils) grow from nodes. This is flower initiation. Simultaneously there's a height surge: plant grows another 20-30 cm in first 2-3 flower weeks. This "stretch" is normal—plan for it (don't place light too close!). PPFD in early flower: 500-700 µmol/m²/s (still slightly under peak).
Week 3-8: Flower Mass Buildup
Weeks 3-8 of flower see large flower clusters forming. Here plants have maximum nutrient hunger. PPFD Peak: 700-900 µmol/m²/s. EC Peak: 1.4-1.6. Reduce nitrogen (don't stop—still needed) but boost phosphorus and potassium. Nutrient focus: K/P dominant for flower structure. A flower fertilizer typically has N:P:K = 1:1.5:2 or similar.
K-Boost and PK Additives: Some growers add extra PK boosters in week 5-8 (e.g. "Blooming Enhancer"). This is optional—a balanced 2-part fertilizer system works fine. If you use boosters, reduce base N slightly to avoid exceeding EC.
Week 9-10: Flower Finalization
In final 1-2 flower weeks your plant has reached its flower goal. No more growth—just maturation. Nutrient hunger slowly drops. You can slightly reduce EC here (1.2-1.4) or switch to a "finish" strategy.
Maturation and Harvest Prep (Weeks 13-16): Trichome Check and Osmotic Finish
Final 2-3 weeks determine taste, potency and cannabinoid profile. These are the most valuable days—done right, major difference compared to done poorly.
Osmotic Finish Approach
A proven concept: in final 2-3 weeks reduce EC to 1.0-1.2 or even plain water ("flush"). This applies mild nutrient stress, forcing the plant to mobilize reserves—trichomes mature faster, cannabinoid profiles more complex, cleaner taste. "Flushing" is debated (scientists say not necessary) but many growers swear by it. Compromise: EC 1.0-1.2 in final 2 weeks = mild stress, not radical.
Trichome Checking (The Most Important Metric)
Inspect flower trichomes every 2-3 days with a 60x-100x magnifier. You'll see three states: (1) Clear/transparent—not yet ripe, THC still building. (2) Milky-white—ripe, THC at peak. (3) Amber—over-ripe, THC converting to CBN (more sedating, less euphoric). Harvest Window: 70-80% milky, 10-20% amber. This is the "Goldilocks zone" for potency and cannabinoid balance. Not too early (clear trichomes), not too late (all amber).
Visual Signs of Ripe Flowers: Leaves yellowish, not green. Pistils/hairs 70%+ orange/brown. Flowers hard and crispy, not soft. Trichomes hold color under magnifier, not clear and shiny.
Harvest Day and Drying
On harvest day cut plants 2-3 hours after lights on (sap flow is low, quality slightly higher). Drying: 50-60% humidity, 18-22°C, 7-10 days until flowers "snap" (break easily, don't bend). Too fast drying (1-3 days) = hasty, chlorophyll residues. Too slow (over 14 days) = mold risk. 7-10 days is the gold zone.
Light Schedule Table: PPFD and DLI per Phase
Light is one of the top-3 yield drivers (alongside nutrients and climate). This table shows science-based targets:
| Phase / Week | Light Cycle | PPFD (µmol/m²/s) | DLI (Daily Light Integral) | Light Distance (approx) | Notes |
|---|---|---|---|---|---|
| Germination (0-7d) | 16-18h | 0-100 (minimal) | 0-7 | None or 1m+ away | Can germinate completely dark |
| Seedling (1-2 wk) | 18-20h | 150-250 | 10-18 | 40-60 cm | Increase gradually, don't shock |
| Veg early (3-4 wk) | 18h/6h | 350-450 | 23-32 | 30-40 cm | Fast ramp-up in this phase |
| Veg late (5-6 wk) | 18h/6h | 450-600 | 29-43 | 25-35 cm | Full power then switch |
| Flower early (7-8 wk) | 12h/12h | 500-700 | 21-30 | 25-35 cm | Switch triggers flowering |
| Flower mid (9-12 wk) | 12h/12h | 700-900 | 30-39 | 20-30 cm | Peak PPFD and DLI |
| Flower late (13-14 wk) | 12h/12h | 600-800 | 26-35 | 20-30 cm | Gradual reduction (optional) |
| Maturation (15-16 wk) | 12h/12h | 400-600 | 17-26 | 25-40 cm | Light reduction promotes trichome maturity |
DLI Explained: DLI (Daily Light Integral) is the sum of all photons hitting a surface per day. PPFD × light hours ÷ 3,600 = DLI. Example: 600 µmol/m²/s for 18 hours = 600 × 18 ÷ 3,600 = 3 DLI. Cannabis needs ~30-40 DLI for optimal growth—not more. Higher DLI (over 50) gives no extra yield, just more electricity costs and heat stress.
EC and pH Target Values per Phase: Complete Overview
This is the nutrient bible for a complete cycle. These values are calibrated for coco substrate; for soil slightly reduce (soil is buffered, coco is not).
| Phase / Week | EC Target Range | pH (Coco) | pH (Soil) | N:P:K Focus | CalMag Dosing | Runoff Check |
|---|---|---|---|---|---|---|
| Germination (0-1 wk) | 0 (plain water) | 5.8-6.0 | 6.0-6.5 | None | None | Not needed |
| Seedling (1-2 wk) | 0.4-0.6 | 5.8-6.1 | 6.0-6.5 | Balanced | 2-3 mL/L | EC 0.5-0.8, pH 5.8-6.1 |
| Veg early (3-4 wk) | 1.0-1.2 | 5.8-6.1 | 6.0-6.5 | 2:1:1 (N-heavy) | 3 mL/L | EC 1.0-1.3, pH 5.8-6.1 |
| Veg late (5-6 wk) | 1.2-1.4 | 5.8-6.1 | 6.0-6.5 | 2:1:1 (N-heavy) | 3 mL/L | EC 1.2-1.5, pH 5.8-6.1 |
| Flower early (7-8 wk) | 1.2-1.4 | 5.8-6.1 | 6.0-6.5 | Transition: 1:1:1 | 3 mL/L | EC 1.2-1.4, pH 5.8-6.1 |
| Flower mid (9-12 wk) | 1.4-1.6 | 5.8-6.1 | 6.0-6.5 | 0.5:1.5:2 (K/P-heavy) | 3 mL/L + PK-Boost | EC 1.4-1.7, pH 5.8-6.1 |
| Flower late (13-14 wk) | 1.2-1.4 | 5.8-6.1 | 6.0-6.5 | Less N, less P | 2 mL/L | EC 1.2-1.4, pH 5.8-6.1 |
| Maturation (15-16 wk) | 1.0-1.2 or Flush | 5.8-6.1 | 6.0-6.5 | Minimal or Water | 1 mL/L or None | EC <1.0 (finish phase) |
Runoff Monitoring is Your Best Early Warning: If runoff EC jumps (e.g. week 2 suddenly 2.0 instead of 0.8) something is wrong: under-buffered substrate, input EC too high, or transpiration issues. Caught early you can flush. Caught late it becomes toxicity or chlorosis. Pros measure runoff after every watering in first 3 weeks—that's best quality control.
Common Grow Planning Mistakes and Solutions
-
Mistake 1: EC Ramping Too Fast
Beginners start at full EC 1.4 already in week 3. Result: salt stress, yellowing leaves, slow growth. Solution: EC ramping—increase gradually over 3-4 weeks. Week 3: EC 1.0, Week 4: EC 1.1, Week 5: EC 1.3. The plant adapts itself.
-
Mistake 2: Flower Switch Too Early or Too Late
Switch after only 3 weeks veg = small plant, less yield. After 8 weeks veg = large plant, but risk of excessive stretch, disease susceptibility. Sweet spot: 4-6 weeks. Balances size, grow duration and safety.
-
Mistake 3: Light Too Close to Plant
LED under 20 cm = leaf burn (white spots, yellowing), PPFD overload. Even if technically possible, it's stressful. Keep 25-35 cm distance—optimal for plant without stress.
-
Mistake 4: Not Starting Nutrient Finish on Time
If you run full EC 1.6 through week 14, flowers become over-nourished. Taste gets bitter/sticky, smoke is harsh. Osmotic finish (EC reduction in week 13-14) cleans that up. Start it at least 2-3 weeks before harvest.
-
Mistake 5: Ignoring Trichome Check, Harvesting by Calendar
Some growers say "8-9 weeks flower = harvest" without looking. But every strain and setup is different. One strain ready in 8 weeks, another in 10. A magnifier costs $20—use it! Trichome checking is the safest harvest metric.
Links to Specialist Guides
This guide gives you timeline and targets. For specialist questions use these guides:
- Crop Steering and Generative Growth – How to steer plant morphology with temperature and DLI (vegetative vs generative).
- Harvest Timing: Trichomes and Cannabinoid Maturity – Detailed trichome analysis and the science behind it.
- VPD Calculator and Optimal Climate – Calculate Vapor Pressure Deficit (VPD) for every phase.
- EC Calculator and Nutrient Dosing – Calculate exact EC values for your fertilizer brand.
Frequently Asked Questions about the Grow Cycle
How long does a complete cannabis grow cycle take?
A complete cannabis cycle from germination to harvest typically takes 16-20 weeks. Germination and seedling: 2 weeks. Vegetative phase: 4-6 weeks. Flowering phase: 8-10 weeks. Maturation and harvest prep: 2-3 weeks. The exact timeframe depends on strain (sativa takes longer than indica) and grow conditions. Photoperiod strains need the full 16-20 weeks; auto-flowers can be ready after 10-12 weeks.
When should I switch from veg to flower?
Most growers switch to flower after 4-6 weeks of veg. This is a compromise between plant size and grow duration. Larger plants yield more but take longer and increase risks (space, disease). Rule of thumb: after 4-5 weeks veg the plant is large enough to maximize flowering potential without unnecessarily extending the flower phase. With LED and optimal setup you can also switch after 3 weeks and compensate yield with superior lighting.
What EC should I target during flower?
Early flower (week 1-4): EC 1.2-1.4. Mid flower (week 5-8): EC increases to 1.4-1.6. Late flower (week 9+): reduce EC to 1.0-1.2 for osmotic finish. This increase and reduction is intentional: peak EC in mid-bloom supports maximum nutrient demand for flower development; the reduction at end simulates nutrient stress promoting trichome maturation and flavor complexity. Always monitor runoff—keep below 1.8 EC, otherwise salt stress develops.
How do I know when the plant is ready to harvest?
Trichomes are your best harvest indicator. With a 60x-100x magnifier examine flower trichomes: they start clear, become milky-white and finally amber. Optimal harvest is 70-80% milky and 10-20% amber. Additionally: leaves turn yellowish (normal), pistils become orange/brown at 70%, flowers feel hard and crispy. Don't harvest too early (clear trichomes = low THC) or too late (amber = THC converts to CBN, more sedating). Trichome checking is critical—this is not guesswork.
How many cannabis cycles can I grow per year?
At 16-20 weeks total cycle time you can achieve 2-3 complete cycles per year (depending on harvest readiness and break between cycles). With auto-flowers (10-12 weeks) you fit 4-5 cycles per year. With continuous growing (mother plants, staggered harvest) you can theoretically harvest every 2-3 weeks without stopping the cycle. For beginners: 2 cycles per year. For pros with multi-room setups: 3-4 cycles without stress. The bottleneck is usually not biology but sterilization between cycles and lab resources (cleanliness).