# Purple leaves, bracts or sugar leaves: likely causes and fixes

> Purple leaves, bracts or sugar leaves on cannabis is most often Genetic purple colour (anthocyanin), Normal late-flower fade (senescence) or Cold stress. How to tell them apart, the fix for each and what recovery looks like.

Also called: purple leaves, leaves turning purple, purple buds, purpling, purple sugar leaves.

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

## Likely causes, most likely first

### Genetic purple colour (anthocyanin) (Possible)

- Kind: Genetics; urgency: Low urgency
- Fix: Nothing to fix: purple stems, petioles and bracts are mostly genetic and harmless, brought out by cool nights 5-10 °C (9-18 °F) below day. Purple is bag appeal, not potency.
- Recovery: Leaves stay healthy and green apart from the colour; no spotting.
- 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: [Purple or red stems and leaves on cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/purple-stems-leaves.md)

### Normal late-flower fade (senescence) (Possible)

- Kind: Normal ageing; urgency: Low urgency
- Fix: Nothing to fix in the last 2-3 weeks of flower. Keep feeding at stage strength with N tapered; don't 'flush' (pre-harvest flushing starves the plant while it packs on final weight and resin, and controlled studies show no quality gain). Fade before week 5-6 of flower suggests N was cut too early.
- Recovery: Buds keep swelling and ripening normally while fan leaves fade.
- Confirm: Measure runoff EC against input EC: Water to 10-20% runoff, collect the runoff in a clean cup and measure EC of both with a calibrated meter (1.413 mS/cm standard). Runoff more than ~0.5 mS/cm above input means salt build-up; well below input means the plant is hungry or you are over-leaching. In hydro, compare reservoir EC with the EC you mixed.
- Article: [Yellowing lower leaves on cannabis: a differential](https://genetixbay.com/knowledge/diagnosis/yellowing-lower-leaves.md)

### Cold stress (Less likely)

- Kind: Environment; urgency: Deal with it this week
- Fix: Keep days at 22-28 °C (72-82 °F) and nights no more than 3-6 °C (5-10 °F) cooler and above ~15 °C (59 °F); warm the root zone. Cold-for-colour is real in purple cultivars, but claims of more terpenes or resin are unsupported.
- Recovery: Growth resumes within a week; new leaves come in green.
- Confirm: Check temperature and RH at canopy height with a calibrated sensor: Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point.
- Article: [How cold is too cold for cannabis?](https://genetixbay.com/knowledge/answers/how-cold-is-too-cold.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.