A seedling is running on stored energy and a root system the size of a hair. Your job for two weeks is simple: don't do too much.
The numbers that matter
| Factor | Target | Why |
|---|---|---|
| Light cycle | 18/6 | Vigorous growth without wasted power |
| Light distance | 45–60 cm (LED at ~30 %) | Stretch means too far; bleach spots mean too close |
| Temperature | 22–26 °C day, 18–21 °C night | Cold shocks roots; heat dries seedlings out |
| Humidity | 65–70 % RH | Seedlings drink through leaves while roots develop |
| Water pH | 6.0–6.5 (soil) | Nutrient availability window |
Watering: the part everyone gets wrong
Overwatering kills more seedlings than everything else combined. Roots need oxygen; saturated soil has none.
- Water in a small ring around the stem, not a flood — 30–60 ml is plenty at first
- Let the top 2 cm of medium dry out between waterings (poke a finger in; if it's damp, wait)
- A light pot is a thirsty pot — lift it and learn the weight difference
- Drooping with wet soil = overwatered. Drooping with dry soil = thirsty. Check before you pour.
Feeding: don't
Seed leaves (cotyledons) carry the nutrients a seedling needs for the first 10–14 days, and most starting mixes carry more. Feeding now burns roots. Start at quarter-strength vegetative nutrients only after the third set of true leaves, and only if the plant is pale.
Stretch and how to stop it
A seedling reaching for light gets tall, thin, and floppy. If yours stretches:
- Bring the light closer in small steps (watch the leaves for 24 h after each move)
- Add a gentle fan — light air movement thickens stems
- When transplanting, you can bury a stretched stem up to the first leaves
When seedling stage ends
You're in vegetative growth once the plant is producing full-sized fan leaves at a visible weekly pace — usually week 2–3. That's when feeding, training, and real light begin.