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- Episode focus: Mastering the veg â flower transitionâcalled the most influential ~10-day window of the cycle. Bad transitions cap yield early; you canât âadd daysâ later.
- Core idea: Avoid compounding stress. Moving plants is already stressfulâdonât stack harsh environmental shifts, heavy pruning/topping, high VPD, and high EC all at once.
- Environment fundamentals
- Lighting / DLI matching: Match day-one flower DLI to veg by increasing intensity (PPFD) for the shorter 12-hour photoperiod.
- Typical targets: ~35â40 mol·mâ»ÂČ·dayâ»Âč early, ramp to ~45â50 later.
- VPD matching: Keep VPD close to veg on flip; veg ~0.8â1.0 kPa, then ease into ~1.2â1.4 kPa early flower rather than jumping to dry rooms (1.5â2.0 kPa is too stressful at flip).
- Use VPD strategically to moderate stretch (slightly lower VPD can curb internodal elongation).
- COâ: Less finicky but watch costs. Start around ~800 ppm (veg level), 800â1000 ppm in week 1â2, then up to ~1200â1400 ppm depending on style.
- Humidity & red stems
- Many flower rooms lack humidification; day-one rooms run too dry, forcing excessive transpiration and causing stress cues like red stems.
- Plants are humidifiers, but early in flower theyâre too small to humidify the roomâinstalling steam/dedicated humidifiers prevents early drought stress.
- EC balance with VPD: High EC + high VPD (e.g., 1.5â2.0 kPa) risks toxicity/lockout. If humidity is good, 3.0 EC is fine; if day-one is dry, start with lower EC until humidity improves.
- âBalance over silosâ principle
- Climate (light/VPD/COâ), root-zone, and irrigation are intrinsically linked. Donât change one without adjusting the others (âlaw of minimumsâ thinking).
- Canopy management
- Topping vs. no topping: Depends on planting density and cultivar. Topping can delay flower set 3â5 daysâcostly in a fast crop. Many short/medium cultivars in dense programs perform better untopped.
- Crop registration: Build a simple program to learn genetics (short/medium/tall, heavy/light feeders, topping response).
- Run experiments with new cultivars (e.g., vary drip stakes and leave some untopped) to see true morphology and water response.
- Defoliation/skirting: Do light skirting in the last 5â7 veg days for airflow and access (easier emitter placement). Avoid heavy defol or topping right before flipâit causes hormonal âwhiplash.â
- Trellis best practices: Usually two layers suffice (third is for extremes). Lay both layers in one visit and âhoverâ the second high, then slide down as plants grow.
- Aim for ~1 top per square; redistribute shoots early before