Green Film on Crown of Thorns: Moss/Fungus from Overwatering

Ellen's Crown of Thorns (Euphorbia milii) shows green discoloration spreading up branches and into thorns. She suspects fungus or mold.

Diagnosis: Algae/Moss from Excess Moisture

The green film is almost certainly harmless algae or moss growing on constantly damp bark—not a pathogenic fungus. Crown of Thorns is a succulent; wet conditions promote this surface growth.

Cultural Correction (Primary Treatment)

• Soil: Repot in cactus/palm mix (sandy, low organic matter).
• Watering: Water only when soil is completely dry. Empty saucers immediately.
• Light: Minimum 1 hour direct sun daily; brightest possible indoor light.
• Fertilizer: ¼-½ strength, only during active growth.

Optional Acceleration

Spray with neem oil (organic, controls fungi, mites, insects) to speed green film disappearance, but drying out the plant will resolve it naturally.

Key Principle

Succulents with leaves still need succulent care. "Wet feet" cause most Crown of Thorns problems.