Green Growth on Potting Soil: Algae, Not Fungus

Green Growth on Potting Soil: Algae, Not Fungus

A gardener noticed green clumps with volcanic-like pits (3mm across) on soil surface in pots, now climbing a tree fern trunk. It spreads, flat appearance.

Expert Analysis

This is likely algae, not fungus. Green flat growth on soil surface and stems suggests algae; dries black and crusty. Likes hard-packed, moist, fertilized soil. Ugly but not very harmful. Made of filaments. Fungus/mold is usually white/grey and stringy; fruiting bodies may be round. Artillery fungus makes volcano-shaped fruiting bodies but not green. Best action: remove growth, turn into soil or compost elsewhere. If pots chronically wet, reduce watering, improve drainage. If chronically dry/musty, increase moisture, add lime. Keep mulch under 2 inches. Ensure organic material is damp when applied and area drains well. Bacteria help keep mold in check; some greenish but rarely thick on surface. Moss/lichen possible but algae most likely.