It is a good practice, to clean your deck once a year, in the spring, to remove dirt, mildew and other forms of dis-coloration. Yearly cleaning will ensure that the deck looks nice as well as prolonging the life of the protective coating. Scrubbing your deck with warm soapy water will remove dirt, but diluted household (oxygen based) bleach will be required to remove mildew, as mentioned above.
Most companies also manufacture deck cleaning products to complement the deck finishes they manufacture. These products called cleaners, brighteners or restorers remove different forms of dis-coloration without stripping the finish from the Western Red Cedar. Most of these cleaners can remove dirt and dis-coloration caused by mildew and algae from the surface of cedar, but they vary in their ability to remove iron and tannin stains and weathered (grey) wood from the surface of the deck. Some of these deck cleaners may actually remove wood from the weathered cedar surface and therefore you should take care when using them. Power washers can seriously damage cedar deck surfaces and, as mentioned above, this type of cleaning is NOT recommended for cedar decks or any other cedar product.
A deck that dries after wetting will last longer than one that stays damp. Good maintenance practices for cedar decks include allowing proper water drainage; keeping the surface free of dirt, leaves, pine-needles and other debris; and moving planters, benches and other deck accessories from time to time to permit the deck beneath them to dry thoroughly.