Calla Lily Dormancy & Fungus Troubleshooting in San Jose

A San Jose (Zone 9b) gardener bought a multi-colored calla lily in Feb. By April, leaves yellowed. She learned it was going dormant. Follow-up: white powdery substance on pot/soil during dormancy.

Calla Lily Cycle (Zantedeschia hybrids)

• Bloom: Late winter–spring.
• Dormancy: Late spring–summer (2–3 months). Leaves yellow, wither. Stop watering. Cool, dark, dry storage.
• Rebirth: Fall. Resume water/light. Blooms again.

Dormancy Protocol

1. Stop watering as leaves yellow.
2. Remove dead foliage.
3. Store pot cool (50–60°F), dark, dry. Water barely—just prevent total desiccation.
4. After 2–3 months, move to bright light, resume watering, feed with bone meal.

White Powder Diagnosis

Likely fungal growth (mold/mildew) on decaying organic matter in dormant soil. Not necessarily on the rhizome.

Action

1. Unpot. Locate rhizome (fleshy, tuber-like).
2. If rhizome is firm, plump, odorless: Healthy. Dust with sulfur or copper fungicide. Repot in fresh, well-drained mix.
3. If soft, mushy, smelly: Rotted. Discard.
4. Plant outdoors in San Jose: full sun, well-drained, moist but not soggy. Mulch. Will cycle naturally.

Outdoor Planting in Zone 9b

Callas thrive year-round in San Jose. Plant in ground after dormancy (late summer/fall). They'll naturalize and bloom multiple times yearly.

Don't skip dormancy—it's essential. The fungus is likely secondary; treat the rhizome if healthy.