Quick answer
Keep the light on a long cycle, feed nitrogen, hold temperature at 68 to 78 F, and train the plant before flowers start. Vegetative growth runs from the first set of true leaves until the light flips to 12 hours. Photoperiod plants sit at 18 hours light and 6 hours dark. Autoflowering plants run on their own clock and stay in this stage 2 to 4 weeks.
Light schedule and intensity
- Photoperiod: 18/6 is the common choice. 20/4 and 24/0 also work.
- LED distance: 18 to 24 inches for most panels.
- PPFD: 400 to 600 at the canopy.
- DLI: 25 to 40 mol per square meter per day.
Light leaks in the dark period do not matter at this stage. They matter after the flip, when a short night can stall flower set.
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Temperature and humidity
- Day: 70 to 78 F. Night: 65 to 70 F.
- RH: 55 to 70 percent for young plants.
- RH: drop to 40 to 50 percent by late veg to cut mold risk.
- Airflow: one fan moving air across the canopy, one fan on exhaust.
Vapor pressure deficit of 0.8 to 1.0 kPa fits most veg rooms.
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Water and pH
Soil target is pH 6.0 to 6.5. Coco and hydro target 5.5 to 6.0. Water when the top inch of medium dries. Overwatering shows as drooping leaves with a heavy pot. Underwatering shows as dry, crisp leaf edges.
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Nutrients
Vegetative plants want nitrogen. A common ratio is 3-1-2 or 2-1-2. Target EC of 1.2 to 1.6 for rooted plants in veg, and 0.6 to 1.0 for seedlings and clones. Calcium and magnesium matter under LED. Add 1 to 2 ml per gallon of calmag if leaves show interveinal yellowing.
Training
- Top after 4 to 6 nodes for two main colas.
- Use low stress training to bend stems flat and open the canopy.
- Add a SCROG net at week 3 to 4 of veg.
- Defoliate 10 to 20 percent of large fan leaves at one time. Do not strip the plant.
Topped plants recover in 3 to 5 days under good light.
Pests and disease
Check the underside of leaves every 3 days. Common veg pests are fungus gnats, spider mites, thrips, and aphids. Yellow sticky traps catch adults. Neem oil or insecticidal soap handles light infestations. Powdery mildew shows as white patches when humidity stays above 70 percent with poor airflow.
When to flip to flower
Plants stretch 50 to 100 percent in the first 3 weeks of flower. Flip when the canopy fills about 60 percent of the grow space. Indica-dominant plants double in height. Sativa-dominant plants can triple.
Cannabinoid content at this stage
Cannabinoid levels in vegetative tissue are low. CBDA and THCA build in flower trichomes during weeks 4 to 8 of bloom. Vegetative leaf and stem material is not a CBD source. Harvest timing, not veg length, sets the final CBD or THC content.