Grey mould on houseplants is almost always caused by Botrytis cinerea, a fungus that thrives in cool, damp, still air. You will see it as a fuzzy, dusty grey or beige coat on dying leaves, fading flowers, or stems with damaged tissue. It looks alarming, but for most UK indoor growers it is a manageable problem caused by environmental conditions you can change today. The plant rarely needs to be lost.
What Is Grey Mould?
Botrytis cinerea is a saprophytic fungus, which means it mostly feeds on dead and dying plant tissue. It is most commonly found outdoors on garden roses and strawberries and indoors on cyclamen flowers and bruised African violet leaves. Spores are constantly drifting through the air. They become a problem when they land on tissue that is already weakened, then sit in cool, damp, poorly ventilated conditions long enough to germinate.
This is why grey mould tends to show up in autumn and winter in the UK, when homes get cooler, ventilation drops, and people misting habits stay the same. It is also why a single ailing leaf can become a covered canopy in a week if conditions are right.
Life Cycle of Botrytis
Spores germinate within hours on damp, dead, or damaged plant tissue at temperatures between 10 and 25C. The fungus then sends out fine, white-grey hyphae through the host tissue, breaking it down. Within 3 to 7 days, masses of fresh, fuzzy grey-brown spores form on the surface, ready to disperse. A single infected leaf can release millions of spores into the surrounding air.
This matters for treatment timing. The visible fuzz is the spore-producing stage. If you can remove it before the next round of spores releases, you stop the infection cycle on that plant.
Identifying Grey Mould
What it looks like
Look for a velvety, dusty grey or pale beige coating on:
- Soft, dying leaves, especially older or shaded lower foliage
- Fading flowers, particularly on cyclamen, orchids, African violets and begonias
- Soft, mushy stem sections, particularly at the soil line
- Damaged tissue from pruning cuts or scarring
The mould itself is often preceded by tan or grey water-soaked patches on the leaf or flower. Once the fuzz appears, the disease is well established.
Where to look
Botrytis usually starts on the weakest tissue. Check the lower leaves of plants where the canopy is dense, the spent flowers on flowering plants, and any leaf bases sitting against damp soil.
Where does grey mould come from?
Almost certainly from the air. Spores are everywhere. The realistic question is not where they came from, but why they germinated. Common entry routes that tip an indoor environment in their favour:
- Newly arrived plants brought in cold or damp from a delivery
- Misting heavily in winter without enough airflow
- Sitting plants directly against cold north-facing windows in autumn
- Decaying flowers or leaves left on a plant or compost surface
- Repotting damage that bruises stem tissue
Damage Caused by Botrytis
Grey mould rarely kills a healthy plant outright, but it weakens it. Infected leaves and flowers go limp, brown, and rotten. Heavy infections on stems or crowns can collapse the plant if the tissue is structural. Where the disease really matters is on tender, soft-leaved plants like Begonia, Saintpaulia, Cyclamen, and many Orchidaceae: their tissue rots faster than the fungus can be cleared.
A secondary risk is reinfection. Because Botrytis lives on dead tissue, every infected leaf that falls into the pot becomes a fresh source of spores. Cleanup is part of treatment, not optional.
How to Get Rid of Grey Mould
Immediate steps
- Isolate the plant. Move it away from your other houseplants. Botrytis spreads on air currents and physical contact between leaves.
- Cut out infected tissue. Use clean, sharp scissors. Remove every visibly mouldy leaf, flower, or stem section back to firm, healthy tissue. Bag the cuttings, do not compost them.
- Clear the soil surface. Pick off any fallen leaves, dead petals, or visible mould on the substrate. A 1 to 2cm fresh top dressing of compost can help reset the surface.
- Disinfect your scissors between plants with 70% isopropyl alcohol. Botrytis spores travel easily on tools.
Change the environment
This is where most grey mould infections are actually beaten. The fungus needs three things at once: moisture on the tissue surface, cool temperatures, and still air. Remove any one of those and the spread stops.
- Increase airflow. A small oscillating fan running for a few hours a day in winter dramatically reduces fungal pressure indoors. This is the single most effective change you can make.
- Stop misting infected plants. Misting puts liquid water directly on the leaf surface, which is the worst possible thing for a Botrytis-prone plant. Use a pebble tray or grouped planting for humidity instead.
- Water the soil, not the leaves. Avoid pouring water onto the crown or down into the leaf rosettes of plants like African violets and cyclamen.
- Move plants away from cold glass. A 5cm gap from a single-glazed north-facing window in winter makes a big difference.
- Lift humidity below 70%. Above this, indoor fungal pressure climbs sharply. A simple hygrometer is worth having for diagnosis.
Prevention
Prevention with grey mould is mostly about how you set up the room, not how you treat the plants.
- Quarantine new arrivals for 1 to 2 weeks in a separate room. Inspect for any soft, damp tissue on arrival.
- Remove faded flowers and dying leaves promptly. Do not let them sit on the plant or in the pot.
- Run a fan in shared rooms during autumn and winter, especially in plant-dense corners.
- Keep humidity in a comfortable range. 50 to 65% suits most tropical houseplants without inviting fungal trouble.
- Water early in the day. Wet leaves overnight at cooler temperatures is the worst combination.
- Keep tools clean. A small bottle of isopropyl alcohol next to your scissors is a quiet but useful habit.
If you have repeated grey mould issues across multiple plants, the problem is almost always the room, not the plants. Add airflow, lower the humidity slightly, and clear away dying tissue more often. The fungus has fewer chances to take hold when those three things are in place.