Prevent mildew in indoor herb gardens by ensuring good air circulation using a silent fan to keep moisture moving and prevent stagnant air. Use metal trays at the base of shelves to catch water drips and reduce excess humidity. Avoid overwatering and water in the morning to allow drying during the day. Choose wipeable, moisture-resistant painting finishes on surrounding walls such as eggshell or satin to deter mold growth. Adequate lighting with full-spectrum LEDs and proper spacing also reduces damp conditions that cause mildew, keeping herbs healthy.