Seedling
Definition: A seedling is a young cannabis plant in the stage between sprouting and vigorous vegetative growth, usually the first 2 to 3 weeks of life. Seedlings have small root systems and only a few sets of true leaves, so they need gentle light, warm humid air and careful watering to avoid stretching, drowning or burning.
How Seedling works
The seedling stage starts when the cotyledons open and ends when the plant has roughly four to five sets of true leaves and new growth speeds up noticeably. Most of the action happens underground. Roots must expand before the top can grow fast, which is why seedlings look slow for the first week or two.
Seedling conditions that work
- Light: 200 to 400 PPFD on an 18/6 or 20/4 schedule. Too little light causes stretch; too much bleaches leaves.
- Temperature: 72 to 80°F (22 to 27°C) by day, no lower than 65°F (18°C) at night.
- Humidity: 65 to 75% relative humidity, since small roots cannot pull much water.
- Water: small amounts in a ring around the stem, letting the top inch dry before the next drink.
Common seedling problems
Overwatering is the top killer. Wet, cold media starves roots of oxygen and invites damping-off. Weak light produces leggy seedlings that flop over. Heavy nutrients burn leaf tips, so start in a lightly amended mix or plain starter media, and hold off on feeding until the first two or three true-leaf sets appear.