Grow Guide . lighting . G-10
less than you think,
more than dark.
How much light cannabis clones need is less than most growers assume. A rooted clone wants 200 to 300 PPFD at canopy on an 18 hours on, 6 hours off schedule. Less than that and rooting slows. More and the cut burns.
PPFD measures usable light at the plant surface. Clones want 200 to 300 micromoles per square meter per second. Vegging plants want 400 to 600. Clones get less than half of veg.
Lights on for 18 hours, off for 6 hours. This keeps the plant in vegetative mode. Some growers run 24/0 (always on) which speeds rooting marginally but stresses the cut.
T5 fluorescent tubes at 12 inches above the canopy are the most forgiving. Low-watt LED panels (40 to 100 watts) at 18 to 24 inches work too. Dimmable full-spectrum LEDs are ideal.
Do not put a fresh clone under a 600 or 1000 watt HPS bulb. The intensity will burn the cut within 24 hours. Same for full-strength bar-style commercial LEDs.
Once roots are established (day 10 to 14), start increasing intensity. Day 14: 400 PPFD. Day 21: 500 PPFD. Day 28 onward: 600 PPFD.
In summer, yes, with care. Direct south-facing sun is too intense. Filtered light works.
Raise the light farther away. Most LEDs deliver acceptable clone intensity at 30 to 36 inches above the dome.
For cloning, blue-heavy or full-spectrum. Red spectrum is for flowering.
A standard incandescent or warm LED desk lamp is too low-intensity and wrong spectrum.
Approximations: a 2-bulb T5 fixture at 12 inches above the canopy delivers approximately 250 PPFD.