How often you'll need to reseal or stain your deck depends on its material and finish—but cleaning doesn't. Plan to scrub your deck once a year using a power washer on a low-pressure setting, a brush, and a compatible cleaner. Use a fan tip on the wand, and keep the wand moving to minimize surface damage. Getting rid of mildew may require a specialty product. For daily upkeep, sweep away leaves and debris, and mop up spills right away so that they don't leave stains.