Diseases & rots

White mould on soil

A white fuzzy or crusty layer on the potting mix — usually a harmless mould telling you the surface stays damp.

What you'd see

White, sometimes yellowish, fluffy growth on the surface of the mix
Musty smell in the room
Plant itself looks fine

Where to look

Peat-rich mixes kept moist in low light and still air; fresh compost bags.

How it spreads

Spores are everywhere; the mould grows where moisture and organic matter meet.

Is it really this? Look-alikes

Mineral crust — White crust that is hard and gritty is fertiliser or hard-water salts, not mould.
Perlite — Round white granules, not fuzz.
Mealybugs — Mealybugs are on the plant, not the soil surface.

What's going on

Saprophytic moulds eat decaying organic matter in the mix. They do not attack living roots; they are a sign the surface has stayed wet long enough to grow them.

Why?

This is a reading of your watering and airflow, not a disease of the plant. Respond to the message — more air, less surface wetness — rather than to the mould.

Grandmother's remedies

What people have always done — with an honest note on each.

Scrape and refresh
Scrape off the top centimetre and replace with fresh mix or grit.
Verdict: Effective and tidy.
Cinnamon dusting
Sprinkle ground cinnamon on the surface.
Verdict: Mild antifungal; mostly cosmetic but harmless.

Modern remedies

What growers and extension services reach for today.

Improve airflow and let the surface dry
Fan, brighter spot, water less often.
Verdict: The real fix.

Honest verdict

Harmless to the plant, informative for you. If it keeps returning, your mix holds too much water at the surface for that room.

Prevention

Chunky mix with grit or bark on top
Water by soil check
Move the air