Put on gloves and combine 1/2 cup powdered color safe bleach in 1 gallon of warm water. Mix the solution with your gloved hands until the powdered bleach is completely dissolved.
Wipe the bleach solution onto the mildew stains with a sponge. Scrub larger stains more aggressively, constantly refreshing the bleach solution on your sponge. Rinse off your sponge frequently to wash away mold spores, then continue to wash the mildew stains on your outside fabric furniture.
Allow the powdered bleach solution to sit on your furniture for at least 30 minutes. If the mildew stains are very severe or extensive, leave the bleach solution on the furniture overnight.
Rinse your fabric furniture using an outdoor hose. Rinse in a downward motion so mildew spores are washed off the furniture.
Wick up excess moisture from your outside fabric furniture using large towels. If necessary, move your furniture into the light so the sun can speed the drying process.