# Single-bladed, round or smooth-edged new leaves: likely causes and fixes

> Single-bladed, round or smooth-edged new leaves on cannabis is most often Light leak or interrupted dark period or Re-vegetation from too-long days in flower. How to tell them apart, the fix for each and what recovery looks like.

Also called: single finger leaves, round leaves, reveg leaves, mutant leaves, leaves with no serrations.

Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=new&s=single-blade-leaves

## Likely causes, most likely first

### Light leak or interrupted dark period (Possible)

- Kind: Light; urgency: Act within a day or two
- Fix: Seal the dark period: pinholes, zips, vents and equipment LEDs (tape them), and check the timer. Even dim night light can delay flowering in sensitive cultivars and reveal herm-prone genetics. Use a green headlamp only for brief checks.
- Recovery: Flowering resumes within 1-2 weeks; no new single-blade leaves.
- Confirm: Check for light leaks in the dark period: Sit inside the tent or room for 5 minutes after lights-off until your eyes adjust. Look for pinholes, zips, vents, indicator LEDs on equipment and light under doors. Also confirm the timer actually switches off and stays off.
- Article: [Photoperiod and light leaks: 18/6, 12/12 and the dark period](https://genetixbay.com/knowledge/environment/photoperiod-light-leaks.md)

### Re-vegetation from too-long days in flower (Possible)

- Kind: Light; urgency: Deal with it this week
- Fix: Restore an uninterrupted 12-13 h dark period (13/11 is fine; some cultivars flower at 14-15 h days with ramps). Outdoors, early-season plants under long days re-veg; plant later or use light deprivation.
- Recovery: No new single-blade growth within 2 weeks.
- Confirm: Check for light leaks in the dark period: Sit inside the tent or room for 5 minutes after lights-off until your eyes adjust. Look for pinholes, zips, vents, indicator LEDs on equipment and light under doors. Also confirm the timer actually switches off and stays off.
- Article: [How do I reveg a plant after harvest?](https://genetixbay.com/knowledge/answers/how-to-reveg-a-plant.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.