Help with moldy deck from bad boiled linseed oil job
So your posts are in direct contact with the ground? Not pressure treated? Maybe redwood or cedar? You might just wait until its warm enough to deal with. Best bet may be to pressure wash and strip the deck then sand and reseal or stain or whatever your preferred covering is. If you can keep the deck dry and warm for a sealing project now, you could do it now. They make a deck wash that will clean your deck, very similar to a bleach solution. You need to kill the mold before you apply another treatment. If mold on the posts is an issue, you need to look into a different post, either pier blocks or replacing the posts with pressure treated wood.