Cannabis Vegetative Stage: Light, Nutrients, and Timing Guide
The cannabis vegetative stage runs from seedling to flower. Learn light schedules, nutrient ratios, watering, training, and when to flip to 12/12.
The vegetative stage is when a cannabis plant builds roots, stems, and leaves instead of flowers. During veg you run 18 hours of light and 6 hours of dark, hold the canopy at 75 to 85 degrees F with 45 to 65 percent humidity, feed a nitrogen-heavy nutrient mix at pH 6.0 to 6.5 in soil, and train branches with topping or low-stress training so light reaches every bud site. Most home grows stay in veg for 3 to 8 weeks before flipping to a 12/12 flowering cycle.
What Is the Vegetative Stage of a Weed Plant?
Veg begins once the seedling grows its first set of true, multi-fingered leaves and ends when you switch the light cycle to 12/12. The plant stops stretching upward and starts building flower sites instead. Indoors this stage lasts exactly as long as you allow it, from three weeks for a fast sea of green to eight weeks or more for a large scrog.
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What Light Schedule and Intensity Do Vegging Plants Need?
Run 18 hours on and 6 hours off for fast, steady growth, or 20/4 if you want a little more bulk. Vegetative plants want more light than seedlings but less than flowering plants. Aim for 300 to 600 PPFD at the canopy with LED fixtures, or about 400 to 600 watts of HID light per square meter.
When to Switch Cannabis from Vegetative to Flowering
How Far Should Grow Lights Hang Above the Canopy?
Start LEDs 24 to 30 inches above the top leaves and lower them slowly while watching for bleaching or taco-shaped leaves. HID lamps run hotter, so keep them 18 to 24 inches away with strong exhaust.
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What Temperature and Humidity Should You Hold During Veg?
Keep daytime temps between 75 and 85 degrees F and nighttime temps within 10 degrees of that. Humidity of 45 to 65 percent keeps transpiration steady and helps the plant move calcium and magnesium. Higher humidity helps clones and seedlings early on, but drop it before flower to reduce bud rot risk.
How Do You Feed and Water a Plant in Veg?
Vegetative plants are nitrogen hogs. Use a grow formula with an NPK around 3-1-2 or 4-2-3, and raise the strength gradually from a quarter dose to full dose over two or three weeks. Water when the top inch of soil feels dry, and always water until you see 10 to 20 percent runoff in coco or hydro.
What pH and EC Should You Target?
Soil growers should keep runoff pH between 6.0 and 6.5, while coco and hydro growers aim for 5.8 to 6.2. EC during veg usually runs 1.2 to 2.0, depending on strain and light intensity.
Should You Train or Prune During the Vegetative Stage?
Yes, veg is the best window to shape the plant. Topping above the fourth or fifth node creates two main colas and a wider canopy. Low-stress training ties branches flat to spread light and raise yield.
Defoliate sparingly. Remove only leaves that block top bud sites or touch the medium. Heavy stripping in veg slows growth and can shock a young plant.
What Problems Show Up in Veg and How Do You Fix Them?
- Yellow lower leaves: usually nitrogen deficiency or pH drift, so check runoff before adding more food.
- Clawed, dark green leaves: nitrogen toxicity, so flush and cut feed strength.
- Wide node spacing and stretching: raise light intensity or lower the fixture.
- Spotting and fine webbing: spider mites, so treat with neem or insecticidal soap and inspect leaf undersides twice a week.
When Should You Switch a Vegging Plant to Flower?
Flip to 12/12 when the canopy fills about 70 percent of your grow space. Plants stretch 50 to 100 percent during the first three weeks of flower, so leave headroom above the tallest tops.
Vegetative Stage Checklist
- Confirm the 18/6 light cycle and seal any light leaks.
- Measure pH and EC or ppm at every watering.
- Train branches weekly and tuck leaves instead of cutting them.
- Inspect the underside of leaves for pests twice a week.