Calathea Brown Spots: Humidity, Fertilizer, or Fungus?

Brown spots on new calathea leaves (1–3 cm) typically stem from three causes:

1. Low humidity—calatheas need high humidity. Use pebble tray with water (pot not sitting in water) and mist daily.
2. Over-fertilizing—use half-strength fertilizer infrequently. Cut current rate to 1/3 or 1/2.
3. Fungal infection—true round, sunken, yellowish spots. Treat with fungicide (neem works for fungus, insects, mites). Remove infected leaves.

Watering

Water when top surface is dry. Avoid watering the crown.