The best way to deal with mold on urban outdoor cushions is to stop moisture from hanging around in the first place. In a city balcony, rooftop, or small patio, cushions often sit in shade, trap damp air against the furniture, and get caught in sudden rain. So I’d start with the cushion itself: choose mold-resistant fabric, removable covers, and cushions that can be wiped or washed easily. If you’re buying new ones, look for quick-drying foam and breathable covers rather than thick, spongy fills that stay wet for days.
Have a simple rain plan. When heavy rain is coming, bring the cushions inside if you can. If that’s not practical, use a breathable waterproof cover rather than a plastic tarp, because plastic can trap condensation underneath. Also tilt the cushions slightly so water runs off instead of pooling in seams. After rain, don’t just shake them off and put them back—stand them on edge in a sunny, airy spot until they are completely dry.
Airflow matters more than most people think. Don’t leave cushions lying flat against a solid surface for weeks. If your furniture has slats or gaps, use them to your advantage. Prop cushions up when they’re not in use, leave space between the cushion and the frame, and avoid pushing furniture tight against a damp wall. On shaded urban balconies, even a small battery-powered fan or a few hours in direct sun can make a big difference.
Keep them clean and dry. Vacuum crumbs and pollen regularly, because dirt holds moisture. Wash removable covers with mild soap and water, and use diluted white vinegar on small mildew spots if the fabric allows it. Always let covers and foam dry fully before putting them back together. Never store damp cushions in a plastic bag or a sealed box; use a ventilated storage spot or bring them indoors only after they are bone dry.
If you live in a humid city, check the cushions after foggy mornings or cool nights. Wipe off condensation and let them air out before people sit on them. For long rainy spells, store cushions indoors in a dry, ventilated area, and use a moisture absorber nearby only if the space is enclosed. If mold does appear, treat it quickly, dry the cushion completely in the sun, and don’t put it back on the furniture while it’s still even slightly damp. A little routine care is much easier than replacing moldy cushions later.