If you have a wood deck, you know how quickly it begins to discolor. Mold and dirt change the wood from inviting to frightening very quickly. Get a stiff-bristeled brush with a long handle, and in a bucket mix 1 part bleach to 3 parts water. Make sure to cover any plants before cleaning. Put on some protected gloves and clothes that you care nothing about and scrub your deck down with the solution. Rinse occassionally with the garden hose. This will whiten the wood and kill off any mold. Make sure that the deck fully dries before applying any sealant.