Lay the open umbrella on its side and use a broom to sweep off excess dirt.
Hose the umbrella down. Place a capful of laundry detergent into a bucket of warm water and swish around to mix. Use a stiff bristled brush to loosen the dirt and grime. Don't scrub too vigorously because you may damage or remove the protective coating on your umbrella.
Rinse well. Be sure to get all the soap off your umbrella.
Sprinkle baking soda on remaining stains. Let the baking soda sit for about 10 minutes then rinse off.
Remove mold or mildew stains with a 50-50 solution of bleach and plain water. Test the umbrella in a small spot for colorfastness. If the color doesn't fade, apply bleach and scrub off the mold and mildew.
Dry the umbrella by letting it sit open in the sun for a few hours before storing it.