A common fabric used in various outdoor items, canvas is durable and -- with the proper care -- will last for years. Since outdoor fabrics typically deal with excess moisture, moss will likely begin to grow on the canvas. Moss is a non-flowering plant that itself does little damage to the canvas beyond staining. However, the water the moss traps between itself and the fabric will provide the perfect breeding ground for fungus such as mould. The mould will eat away at the canvas, deteriorating it beyond repair.
Brush the large pieces of moss off the canvas with a broom. Alternatively, hose the moss off the surface.
Apply white vinegar to the remaining moss and let soak for 10 minutes. Scrub the area with a soft-bristled scrub brush while continuing to apply vinegar.
Rinse the canvas clean with water. Repeat the process if any green, mossy residue remains on the canvas.
Remove the large, surface moss off the canvas with a broom or hose.
Combine 1 gallon of lukewarm water and 1 cup of oxygen bleach in a plastic bucket. Stir the contents together until the oxygen bleach dissolves.
Saturate a soft-bristled scrub brush or sponge in the mixture and scrub the moss off the canvas. Let the mixture sit on the area for 10 minutes.
Rinse the mixture off the canvas with a hose. Continue scrubbing with the oxygen bleach mixture if moss remains.