# White fuzz or threads on the medium surface: likely causes and fixes

> White fuzz or threads on the medium surface on cannabis is most often Harmless white fungus (mycelium) on organic medium. How to tell them apart, the fix for each and what recovery looks like.

Also called: white fuzz on soil, mould on soil, white web on top of soil, white mycelium in pot.

Run the checker with this sign: https://genetixbay.com/knowledge/diagnose/?at=roots&s=white-fuzz-medium

## Likely causes, most likely first

### Harmless white fungus (mycelium) on organic medium (Likely)

- Kind: Root zone; urgency: Low urgency
- Fix: Usually beneficial or harmless decomposers on mulch and organic matter. Let the surface dry more between waterings and improve airflow; scrape it off if it bothers you.
- Recovery: Plant stays healthy; fuzz recedes as the surface dries.
- Confirm: Lift the pot and check moisture at depth: Lift the pot right after a full watering to learn its wet weight, then lift before each watering. Water when it is clearly lighter (about half the added water gone). Push a finger or a moisture probe 5 cm (2 in) down. Heavy for 3-4+ days with droop: overwatering. Very light with limp papery leaves: thirst.
- Article: [What is the white fuzz on top of my soil?](https://genetixbay.com/knowledge/answers/white-fuzz-on-soil.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.