# Leggy seedling with a long, thin stem: likely causes and fixes

> Leggy seedling with a long, thin stem on cannabis is most often Not enough light. How to tell them apart, the fix for each and what recovery looks like.

Also called: stretched seedling, seedling too tall, seedling falling over thin stem.

Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=stems&s=leggy-seedling

## Likely causes, most likely first

### Not enough light (Likely)

- Kind: Light; urgency: Low urgency
- Fix: Bring PPFD to stage targets: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s. Yield rose linearly with PPFD from 120 to 1,800 in a controlled trial. Lower canopy buds under ~300-400 µmol/m²/s make larf: thin or lollipop the shaded bottom, or train flat.
- Recovery: New internodes shorten within a week; denser buds on the following weeks of growth.
- Confirm: Measure PPFD at the canopy top: Use a quantum (PAR) meter, or a calibrated phone app as a rough guide, at the top leaves in a 5-9 point grid. Compare with the stage target: seedlings 100-300, veg 300-700, flower 800-1,200 µmol/m²/s at ambient CO2. Bleaching and taco at the top above ~1,100 point to light; stretch below ~300 in veg points to too little.
- Article: [Stretchy, leggy cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/stretching.md)

## Note

Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth.