Short answer
White mold on the soil surface of a ZZ plant is usually a harmless saprophytic fungus thriving on organic matter in damp, poorly ventilated soil. The most common fix is to allow the soil to dry out completely between waterings and increase airflow around the base of the plant.
ZZ plants (Zamioculcas zamiifolia) are highly drought-tolerant with thick, water-storing rhizomes, so seeing white fuzz on the surface is a clear signal that your soil is remaining moist for too long. While usually cosmetic, this fuzz indicates that your watering routine is pushing the boundaries of what this desert-adapted plant prefers, which could eventually lead to lethal rhizome rot.
Because ZZ plants require total drying between waterings, consistently damp soil provides the perfect breeding ground for mold spores. If the topsoil stays wet, these fungi break down the organic peat or coco coir in your potting mix.
Check: Stick your finger two inches into the soil; if it feels damp or cool, your substrate is holding too much water for this species.
Fix: Increase the duration between waterings and ensure your pot has adequate drainage holes; if the soil stays wet for more than a few days, repot into a chunkier mix with more perlite or pumice.
ZZ plants are often placed in dark corners with stagnant air. Without enough air movement, moisture lingers on the soil surface, allowing mold colonies to establish themselves easily.
Check: Check if the area around the pot feels humid or stuffy compared to the rest of the room.
Fix: Move the plant to a spot with better light and natural air movement, or place a small fan nearby to help the surface soil dry faster.
Some commercial potting soils contain high amounts of untreated compost or woody debris that naturally harbor mold spores. In a moisture-retaining environment, these spores bloom quickly.
Check: Look for small white threads or patches appearing immediately after a fresh watering on new, previously unused soil.
Fix: Scrape off the top layer of affected soil and replace it with a coarse, well-draining grit or top-dress with decorative pebbles to keep the surface dry.
When to worry
Worry immediately if the white fuzz is accompanied by soft, mushy stems at the soil line, which indicates the rhizomes are rotting, or if the mold is spreading rapidly to the foliage.
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Diagnose my ZZ PlantUsually, the mold is just a scavenger feeding on organic matter and won't hurt the plant directly. However, it is a warning sign that your soil is too wet, which is the primary cause of death for ZZ plants.
It is rarely necessary. Instead of chemicals, focus on adjusting your watering schedule to let the plant dry out, which kills the fungus naturally by removing its preferred habitat.
Only if the soil is so compacted or peaty that it never dries out. Otherwise, simply scraping off the mold and letting the plant go bone-dry before the next watering is sufficient.
Consistent with guidance from: Royal Horticultural Society, University of Missouri Extension.