First off, cleaning your pergola to prepare it for the winter season, you may not have to do all of these steps, if you have taken good regular care of it, maybe it is all set.
Hose it! Using a low pressure power washer is best but be sure to move all outdoor furniture and plants that surround it first. If you have outdoor plants that are lucky enough to survive the winter you don't want to wash them and the furniture, if you already winterized it you don't want to start the process again.
Clean it! Using a light bleach water solution will do the trick, using 1part bleach to 10 parts water, if you use more bleach you will risk bleaching the wood. Bleach is the best natural cleaner as it will kill any mold and mildew that has decided to take up residence in your wood.
Rinse it! Once again using your low pressure power washer and give it a good rinse, and remember, no plants near, plants do not respond well to bleach!
Take a look! Now is the time to take a quick walk around, are there any damages or splitting, any hard to clean spots, if so give it a scrub. If there was splitting or cracking in the wood you will need to wait till it is dry and then sand it down.
Stain it! I know it has probably already been stained when you put it up, but it can't hurt, you never know how wet the winter might be. Unless it already is filled with plants crawling up, this is a good time to give it a once over, who knows, next winter it may already be filled with plants winding all the way up it.
Screw it! Grab your screwdriver and tighten each and every loose screw, just be careful if they don't need it you don't want to strip the wood.
Pergolas are part of your home, your outdoor home, and they can be such beautiful additions to your deck, patio or walk way, allowing for growing plants to climb up their arch. It is easy if not properly maintained for them to become unpleasant to look at, natural wear and tear, from wet winters to extremely sunny summers. Be sure to take care of it this winter and every season after that, the last thing you want is to walk outside your own home and see yours falling apart.