# Flowering not starting or very slow after the flip: likely causes and fixes

> Flowering not starting or very slow after the flip on cannabis is most often Light leak or interrupted dark period or Long-flowering or light-sensitive cultivar. How to tell them apart, the fix for each and what recovery looks like.

Also called: not flowering, still vegging after flip, no pistils after 3 weeks, won't flower.

Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=buds&s=flowering-delayed

## Likely causes, most likely first

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

- 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)

### Long-flowering or light-sensitive cultivar (Less likely)

- Kind: Genetics; urgency: Low urgency
- Fix: After the flip there is a 10-14 day transition before flowering really starts (up to 3 weeks in slow cultivars). Count from the flip and add the transition; flip earlier or train flatter for big-stretch cultivars.
- Recovery: Pistils at the top of the main stem by about 3 weeks after the flip.
- 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.
- Confirm: Compare with siblings or the same cut: Put the affected plant beside siblings or clones of the same cut in the same conditions. A trait shared by all of a cultivar (purple stems, foxtailing, pale colour) is genetic; a problem on one plant points to its roots, a virus or its genetics; a problem on every cultivar points to the environment or feed.
- Article: [The flip isn't day 1 of flower: the 10–14 day transition and how to count it](https://genetixbay.com/knowledge/environment/flip-to-flower-transition.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.