Canvas umbrellas can accumulate a great deal of dirt and grime throughout the year, even when in winter storage. Even if it doesn't look salvageable when you take it out for use in the spring, do not throw it away just yet. With but a little hard work, you will be able to make it look good as new.
Remove the canvas from the frame. The canvas on your canvas umbrella is removable. You can carefully take it off the frame to clean it properly.
Soak your umbrella canvas. Fill an empty, clean garbage can with water and bleach (if it is white), or OxiClean or other color-safe bleach (if it is colored). Soak the canvas umbrella cover for 1 to 2 hours.
Put it in the washing machine. A canvas umbrella cover should be able to withstand a washing machine cycle. After soaking, place it in the washing machine, add your regular detergent and bleach or OxiClean. It should come out in like-new condition.
Clean the umbrella frame. Hose off the umbrella frame with a medium-pressure water hose, then wipe it down with glass cleaner to remove any excess dirt or grime. If it is very dirty or has mold on it, use bathroom cleaner that contains bleach. Don’t forget to wear gloves.
Put the canvas back on the frame. While your canvas umbrella cover is still wet, put it back on the frame, place it in the stand and open it so it can air-dry.
If your canvas umbrella does not come apart, you can scrub it with a bleach (or bleach substitute) solution, let it set and then hose it down with a medium spray.