The answer varies based on the current condition of your wood. If you do decide to pressure wash your deck, use pressure between 1,000 or 1,200 psi. Also be sure to work with the grain and never against it, as it will cause damage to the wood's surface and splinters.
If you don't have easy access to a pressure washer or have to pay to rent one, we recommend DEFY Wood Cleaner instead. It's easy to use and will clean deep into the wood, which makes your next coat of wood stain more effective and more beautiful.