Diseases & rots

Grey mould (Botrytis)

Fuzzy grey fur on flowers, soft stems and dead tissue in cool, damp, still air.

What you'd see

Grey-brown fuzzy growth on faded flowers, leaf bases or soft stems
Soft, water-soaked patches that spread quickly
A puff of grey dust (spores) when disturbed

Where to look

Dying petals, fallen leaves left on the soil, crowded seedlings, and cool damp rooms in winter.

How it spreads

Airborne spores everywhere; needs dead or wounded tissue and moisture to start.

Is it really this? Look-alikes

Powdery mildew — Mildew is white and flat on living leaves; botrytis is grey, fuzzy and on dying tissue.
Soil mould — White fluff on the soil surface is saprophytic mould, not botrytis.

What's going on

Botrytis cinerea is an opportunist. It colonises dead or dying tissue first, then invades healthy tissue from that base when conditions are cool (10–20 °C) and humid with still air.

Why?

The fungus needs a dead foothold, so hygiene is the whole game: no spent flowers, no fallen leaves on the soil, no damp crowding. Remove the foothold and the fungus has nowhere to begin.

Grandmother's remedies

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

Deadhead and tidy
Remove faded flowers and fallen leaves promptly; keep the soil surface clear.
Verdict: The most effective measure there is.
Air the room
Open a window or run a fan; do not cluster plants in a cold corner.
Verdict: Highly effective.

Modern remedies

What growers and extension services reach for today.

Cut back to clean tissue
Remove affected parts well below the visible mould with sterile scissors.
Verdict: Necessary.
Fungicide
Rarely warranted indoors; use per label for valuable plants.
Verdict: Botrytis resists many fungicides; cultural fixes matter more.

Honest verdict

Grey mould is a symptom of cool, damp neglect more than a disease that strikes. Warmth, air and tidiness stop it.

Prevention

Deadhead flowering plants
Clear fallen leaves off the soil
Avoid cold, still, damp windowsills in winter
Do not overcrowd cuttings