Vegetative Stage — the weeks that decide your harvest
In veg, the plant builds the frame for everything to come. Getting light, training and repotting right often doubles the yield — without a single extra watt.
TL;DR: Photoperiod 3–8 weeks at 18/6, autoflower 3–4 weeks automatic. Temp 22–28 °C, VPD 0.8–1.2 kPa, EC 1.2–1.8. Topping wk 3, continuous LST, SCROG 1 week before 12/12.
What happens biologically
After germination the plant enters veg: true leaves, root system, auxin for stretch. Blue-light demand (400–500 nm) is highest.
Photoperiod strains stay in veg while getting ≥14 h light. Below 12 h → flower. Autoflowers flower after ~3–4 weeks regardless.
Light schedule
Standard 18/6. Alternative 20/4. 24/0 only for very young LED-lit seedlings.
Intensity: seedling 100–200, young veg 300–500, late veg 500–700 μmol/m²/s. DLI 20–30 mol/m²/day.
Climate — VPD, temperature, CO₂
Day 22–28 °C, night 18–22 °C. Humidity 55–70 %. VPD target 0.8–1.2 kPa. CO₂ boost 800–1200 ppm only with >600 μmol.
Repotting
Seedling → 0.5 L. First repot 3–5 L at 3–4 nodes. Final 11–25 L indoor, 30–50 L outdoor. Autoflowers straight into final pot.
FAQ
How long to veg?
Photoperiod 4–8 weeks; autoflower 3–4 weeks fixed.
Should I top?
Recommended: +20–40 % yield thanks to 2–8 equal colas instead of one dominant one.
What is VPD?
Vapor Pressure Deficit: 0.8–1.2 kPa = optimal transpiration and nutrient uptake.
Lower leaves yellowing?
Normal if limited to old fan leaves. Alarming when it hits young growth.