You can do it... I just got thru doing my deck and fence and it looks brand new..mine is 9 years old.. Some people will frown on this but... I used mold/mildew cleaner that I got at Home Depot made by Armor All... used to be marketed as a "deck cleaner".. it is 2.88 a gallon, you spray it on with a pump sprayer and watch the old gray run off before your eyes.. hose it off very good afterwards. In some spots I had to put it on a couple of times to get it clean. I let it dry for several days and used Deckscapes semi-transparent oil based stain/sealer on my fence and deck so the color would match. I am more then happy with the results. I did brush the stain/sealer on.
Here are my results...