Fittonia Mold: Grey Mould on Leaves or Fungus on the Soil?

Fittonia, the nerve plant, needs humid air. The RHS fittonia growing guide recommends a terrarium, bathroom or kitchen for that reason. The same guide warns that grey mould (Botrytis) can thrive in humid environments. That trade-off is why mould shows up on nerve plants, especially in jars and closed terrariums.

Start by working out where the mould is. Fuzz on the leaves, fuzz on the soil and rot at the roots need different fixes.

Which mould do you have?

What you see	Most likely	Next check
Grey-brown fuzz on soft, browning leaves or stems; dust-like spores when touched	Grey mould (Botrytis)	Dead leaves, crowding, condensation
White or yellowish fuzzy growth on the mix surface, plant looks healthy	Saprophytic soil fungus	How long the surface stays wet
Hard, crusty white or grey deposit on mix or pot rim	Mineral or fertilizer salts	Water source and feeding
Stems collapsing at the base, yellowing, dark soft roots	Root rot	Unpot and inspect the roots
Brown spots on otherwise firm leaves	Leaf spot	Wet leaves, poor airflow
White cottony clusters in leaf joints	Mealybugs, not mould	Check stems and leaf undersides

Clemson HGIC’s gray mold factsheet says Botrytis starts as brown to grey spots that turn fuzzy as grey spores form. A cloud of spores may rise when you pick an infected leaf. It favours old, weak or dying tissue.

Clemson’s houseplant disorders factsheet separates crusty salt deposits from the white or yellow mold-like growth of saprophytic soil fungi. NC State Extension notes that fittonia is susceptible to leaf spots and that overwatering can cause root rot.

Why nerve plants get mouldy

Fittonia sits at the edge of two needs. The RHS says the plant needs moist air, or its leaves turn brown. Clemson says grey mould thrives in shaded, crowded plantings with poor air circulation, and on dead plant material.

A low, dense mat of stems in a closed jar has all of that. Dropped leaves rot on the wet surface. NC State even notes that if humidity is too high, fittonia leaves may wither.

Clear grey mould from leaves and stems

1. Remove affected material. The RHS advice for grey mould is to remove any affected plant material. Cut back to clean, firm stems.
2. Pick up debris. Take dead leaves and stems off the mix. Clemson calls sanitation one of the best ways to reduce gray mold.
3. Keep water off the leaves. Clemson notes the fungus spreads by splashing water. Water the mix at the edge of the pot.
4. Let air in. UNH Extension advises lifting the lid of closed terrariums and cloches occasionally to prevent excess moisture build-up. Vent a jar that stays fogged.
5. Thin crowded plantings. Space pots apart, or take out a section of a dense clump.
6. Rescue healthy pieces. If the centre of a clump has died, the RHS suggests dividing it and replanting the healthy sections. It also describes taking 5 cm (2 in) cuttings from strong stems.

Clemson says chemical control of grey mould is rarely needed. Cleanup and airflow come first.

Deal with fungus on the soil surface

Clemson’s factsheet treats the white or yellow mold-like growth of saprophytic soil fungi as different from salt crust. These fungi feed on organic matter and dead debris, not on the plant.

Scrape off the fuzzy layer and any dead leaves under it. Let the top of the mix dry slightly before the next watering. Move the plant somewhere brighter but out of direct sun. Our mold on houseplant soil guide covers surface fungus in more detail.

Do not swing to bone-dry mix. The RHS notes that a lack of water makes fittonias droop or wilt. They usually recover after a thorough watering, provided it has not gone on too long. Aim for evenly moist mix, never waterlogged.

If the stems collapse at the base

Mould on the surface plus yellowing and collapsing stems needs a root check. NC State links yellowing leaves and root rot in fittonia to overwatering.

Slide the plant out of the pot. Clemson advises cutting out the infected roots when only a few are affected, then repotting in sterile soil. If most roots are dark and soft, root cuttings from the healthiest stems instead.

Set it up to stay mould-free

The RHS growing guide gives the basics:

• Bright light out of direct sun; near a north- or east-facing window is ideal.
• At least 15 °C (60 °F), ideally above 17 °C (63 °F), away from cold draughts and radiators.
• Moisture-retentive, peat-free houseplant compost.
• A pot only slightly larger than the root ball, to avoid overpotting.
• Less frequent watering in terrariums and sealed containers, where the air stays humid.

Fittonia is safe to keep around pets. The ASPCA lists the nerve plant as non-toxic to dogs, cats and horses.

For more nerve plant pages, see the fittonia hub.

Related guides

Other fittonia problems we cover: overwatering, brown tips, curling leaves.

References

• RHS: How to grow fittonia
• NC State Extension Gardener Plant Toolbox: Fittonia albivenis
• Clemson Cooperative Extension: Gray Mold (Botrytis Blight) on Flowers, Fruits, and Vegetables
• Clemson Cooperative Extension HGIC 2251: Houseplant Diseases & Disorders
• UNH Extension: How can I increase humidity indoors for my houseplants?
• ASPCA Animal Poison Control Center: Nerve Plant