Lay an old sheet in a sunny location. Set the moldy cushions on top of the sheet and leave them there for four to five hours, turning the cushions over halfway through the allotted time so both sides can dry. The sun kills mold spores.
Brush off mold spores using a natural-bristle brush. Do this outdoors, away from your patio, to avoid transferring mold to other surfaces.
Mix 3/4 cup all-fabric bleach, 2 tsp. dish-washing detergent and 1 gallon warm water in a bucket. Put on rubber gloves to protect your hands from coming in contact with mold. Dip the scrub brush into the bleach solution and then scrub the cushions to remove mold and its accompanying stains.
Dampen a clean cloth with water. Repeatedly wipe off the surface of the cushions, rinsing the cloth as needed.
Press a clean, dry cloth into the cushions to absorb moisture. Prop up the cushions in a dry location to allow them to air-dry completely. Rotate the cushions to ensure air circulates around them and dries all sides.